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Current Biology
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ISSN (Print) 0960-9822
Published by Elsevier Homepage  [3185 journals]
  • Forebrain Dopamine System Regulates Inner Ear Auditory Sensitivity to
           Socially Relevant Acoustic Signals
    • Abstract: Publication date: Available online 13 June 2019Source: Current BiologyAuthor(s): Jonathan T. Perelmuter, Anthony B. Wilson, Joseph A. Sisneros, Paul M. ForlanoSummaryDopamine is integral to attentional and motivational processes, but studies are largely restricted to the central nervous system. In mammals [1, 2] and fishes [3, 4], central dopaminergic neurons project to the inner ear and could modulate acoustic signals at the earliest stages of processing. Studies in rodents show dopamine inhibits cochlear afferent neurons and protects against noise-induced acoustic injury [5, 6, 7, 8, 9, 10]. However, other functions for inner ear dopamine have not been investigated, and the effect of dopamine on peripheral auditory processing in non-mammalians remains unknown [11, 12]. Insights could be gained by studies conducted in the context of intraspecific acoustic communication. We present evidence from a vocal fish linking reproductive-state-dependent changes in auditory sensitivity with seasonal changes in the dopaminergic efferent system in the saccule, their primary organ of hearing. Plainfin midshipman (Porichthys notatus) migrate from deep-water winter habitats to the intertidal zone in the summer to breed. Nesting males produce nocturnal vocalizations to attract females [13]. Both sexes undergo seasonal enhancement of hearing sensitivity at the level of the hair cell [14, 15, 16], increasing the likelihood of detecting conspecific signals [17, 18]. Importantly, reproductive females concurrently have reduced dopaminergic input to the saccule [19]. Here, we show that dopamine decreases saccule auditory sensitivity via a D2-like receptor. Saccule D2a receptor expression is reduced in the summer and correlates with sensitivity within and across seasons. We propose that reproductive-state-dependent changes to the dopaminergic efferent system provide a release of inhibition in the saccule, enhancing peripheral encoding of social-acoustic signals.Graphical Graphical abstract for this article
  • A Septin Double Ring Controls the Spatiotemporal Organization of the ESCRT
           Machinery in Cytokinetic Abscission
    • Abstract: Publication date: Available online 13 June 2019Source: Current BiologyAuthor(s): Eva P. Karasmanis, Daniel Hwang, Konstantinos Nakos, Jonathan R. Bowen, Dimitrios Angelis, Elias T. SpiliotisSummaryAbscission is the terminal step of mitosis that physically separates two daughter cells [1, 2]. Abscission requires the endocytic sorting complex required for transport (ESCRT), a molecular machinery of multiple subcomplexes (ESCRT-I/II/III) that promotes membrane remodeling and scission [3, 4, 5]. Recruitment of ESCRT-I/II complexes to the midbody of telophase cells initiates ESCRT-III assembly into two rings, which subsequently expand into helices and spirals that narrow down to the incipient site of abscission [6, 7, 8]. ESCRT-III assembly is highly dynamic and spatiotemporally ordered, but the underlying mechanisms are poorly understood. Here, we report that, after cleavage furrow closure, septins form a membrane-bound double ring that controls the organization and function of ESCRT-III. The septin double ring demarcates the sites of ESCRT-III assembly into rings and disassembles before ESCRT-III rings expand into helices and spirals. We show that septin 9 (SEPT9) depletion, which abrogates abscission, impairs recruitment of VPS25 (ESCRT-II) and CHMP6 (ESCRT-III). Strikingly, ESCRT-III subunits (CHMP4B and CHMP2A/B) accumulate to the midbody, but they are highly disorganized, failing to form symmetric rings and to expand laterally into the cone-shaped helices and spirals of abscission. We found that SEPT9 interacts directly with the ubiquitin E2 variant (UEV) domain of ESCRT-I protein TSG101 through two N-terminal PTAP motifs, which are required for the recruitment of VPS25 and CHMP6, and the spatial organization of ESCRT-III (CHMP4B and CHMP2B) into functional rings. These results reveal that septins function in the ESCRT-I-ESCRT-II-CHMP6 pathway of ESCRT-III assembly and provide a framework for the spatiotemporal control of the ESCRT machinery of cytokinetic abscission.Graphical Graphical abstract for this article
  • Mass Seasonal Migrations of Hoverflies Provide Extensive Pollination and
           Crop Protection Services
    • Abstract: Publication date: Available online 13 June 2019Source: Current BiologyAuthor(s): Karl R. Wotton, Boya Gao, Myles H.M. Menz, Roger K.A. Morris, Stuart G. Ball, Ka S. Lim, Don R. Reynolds, Gao Hu, Jason W. ChapmanSummaryDespite the fact that migratory insects dominate aerial bioflows in terms of diversity, abundance, and biomass [1, 2, 3, 5, 6], the migration patterns of most species, and the effects of their annual fluxes between high- and low-latitude regions, are poorly known. One important group of long-range migrants that remain understudied is a suite of highly beneficial species of hoverfly in the tribe Syrphini, which we collectively term “migrant hoverflies.” Adults are key pollinators [7, 8, 9, 10] and larvae are significant biocontrol agents of aphid crop pests [11], and thus, it is important to quantify the scale of their migrations and the crucial ecosystem services they provide with respect to energy, nutrient, and biomass transport; regulation of crop pests; and pollen transfer. Such assessments cannot be made by sporadic observations of mass arrivals at ground level, because hoverflies largely migrate unnoticed high above ground. We used insect-monitoring radars [12] to show that up to 4 billion hoverflies (80 tons of biomass) travel high above southern Britain each year in seasonally adaptive directions. The long-range migrations redistribute tons of essential nutrients (nitrogen [N] and phosphorus [P]) and transport billions of pollen grains between Britain and Europe, and locally produced populations consume 6 trillion aphids and make billions of flower visits. Migrant hoverfly abundance fluctuated greatly between years, but there was no evidence of a population trend during the 10-year study period. Considering that many beneficial insects are seriously declining [7, 10, 13, 14, 15, 16, 17, 18, 19], our results demonstrate that migrant hoverflies are key to maintaining essential ecosystem services.
  • Oxytocin Signaling in the Central Amygdala Modulates Emotion
           Discrimination in Mice
    • Abstract: Publication date: Available online 6 June 2019Source: Current BiologyAuthor(s): Valentina Ferretti, Federica Maltese, Gabriella Contarini, Marco Nigro, Alessandra Bonavia, Huiping Huang, Valentina Gigliucci, Giovanni Morelli, Diego Scheggia, Francesca Managò, Giulia Castellani, Arthur Lefevre, Laura Cancedda, Bice Chini, Valery Grinevich, Francesco PapaleoSummaryRecognition of other’s emotions influences the way social animals interact and adapt to the environment. The neuropeptide oxytocin (OXT) has been implicated in different aspects of emotion processing. However, the role of endogenous OXT brain pathways in the social response to different emotional states in conspecifics remains elusive. Here, using a combination of anatomical, genetic, and chemogenetic approaches, we investigated the contribution of endogenous OXT signaling in the ability of mice to discriminate unfamiliar conspecifics based on their emotional states. We found that OXTergic projections from the paraventricular nucleus of the hypothalamus (PVN) to the central amygdala (CeA) are crucial for the discrimination of both positively and negatively valenced emotional states. In contrast, blocking PVN OXT release into the nucleus accumbens, prefrontal cortex, and hippocampal CA2 did not alter this emotion discrimination. Furthermore, silencing each of these PVN OXT pathways did not influence basic social interaction. These findings were further supported by the demonstration that virally mediated enhancement of OXT signaling within the CeA was sufficient to rescue emotion discrimination deficits in a genetic mouse model of cognitive liability. Our results indicate that CeA OXT signaling plays a key role in emotion discrimination both in physiological and pathological conditions.Graphical Graphical abstract for this article
  • Retrosplenial Cortical Representations of Space and Future Goal Locations
           Develop with Learning
    • Abstract: Publication date: Available online 6 June 2019Source: Current BiologyAuthor(s): Adam M.P. Miller, William Mau, David M. SmithSummaryRecent findings suggest that long-term spatial and contextual memories depend on the retrosplenial cortex (RSC) [1, 2, 3, 4, 5]. RSC damage impairs navigation in humans and rodents [6, 7, 8], and the RSC is closely interconnected with brain regions known to play a role in navigation, including the hippocampus and anterior thalamus [9, 10]. Navigation-related neural activity is seen in humans [11] and rodents, including spatially localized firing [12, 13], directional firing [12, 14, 15], and responses to navigational cues [16]. RSC neuronal activity is modulated by allocentric, egocentric, and route-centered spatial reference frames [17, 18], consistent with an RSC role in integrating different kinds of navigational information [19]. However, the relationship between RSC firing patterns and spatial memory remains largely unexplored, as previous physiology studies have not employed behavioral tasks with a clear memory demand. To address this, we trained rats on a continuous T-maze alternation task and examined RSC firing patterns throughout learning. We found that the RSC developed a distributed population-level representation of the rat’s spatial location and current trajectory to the goal as the rats learned. After the rats reached peak performance, RSC firing patterns began to represent the upcoming goal location as the rats approached the choice point. These neural simulations of the goal emerged at the same time that lesions impaired alternation performance, suggesting that the RSC gradually acquired task representations that contribute to navigational decision-making.
  • Mycorrhizal Fungi Respond to Resource Inequality by Moving Phosphorus from
           Rich to Poor Patches across Networks
    • Abstract: Publication date: Available online 6 June 2019Source: Current BiologyAuthor(s): Matthew D. Whiteside, Gijsbert D.A. Werner, Victor E.A. Caldas, Anouk van’t Padje, Simon E. Dupin, Bram Elbers, Milenka Bakker, Gregory A.K. Wyatt, Malin Klein, Mark A. Hink, Marten Postma, Bapu Vaitla, Ronald Noë, Thomas S. Shimizu, Stuart A. West, E. Toby KiersSummaryThe world’s ecosystems are characterized by an unequal distribution of resources [1]. Trade partnerships between organisms of different species—mutualisms—can help individuals cope with such resource inequality [2, 3, 4]. Trade allows individuals to exchange commodities they can provide at low cost for resources that are otherwise impossible or more difficult to access [5, 6]. However, as resources become increasingly patchy in time or space, it is unknown how organisms alter their trading strategies [7, 8]. Here, we show how a symbiotic fungus mediates trade with a host root in response to different levels of resource inequality across its network. We developed a quantum-dot-tracking technique to quantify phosphorus-trading strategies of arbuscular mycorrhizal fungi simultaneously exposed to rich and poor resource patches. By following fluorescent nanoparticles of different colors across fungal networks, we determined where phosphorus was hoarded, relocated, and transferred to plant hosts. We found that increasing exposure to inequality stimulated trade. Fungi responded to high resource variation by (1) increasing the total amount of phosphorus distributed to host roots, (2) decreasing allocation to storage, and (3) differentially moving resources within the network from rich to poor patches. Using single-particle tracking and high-resolution video, we show how dynamic resource movement may help the fungus capitalize on value differences across the trade network, physically moving resources to areas of high demand to gain better returns. Such translocation strategies can help symbiotic organisms cope with exposure to resource inequality.Graphical Graphical abstract for this article
  • A Laterally Transferred Viral Gene Modifies Aphid Wing Plasticity
    • Abstract: Publication date: Available online 6 June 2019Source: Current BiologyAuthor(s): Benjamin J. Parker, Jennifer A. BrissonSummaryOrganisms often respond to changing environments by altering development of particular traits. These plastic traits exhibit genetic variation; i.e., genotypes respond differently to the same environmental cues. Theoretical studies have demonstrated the importance of this variation, which is targeted by natural selection, in adapting plastic responses to maximize fitness [1, 2]. However, little is known about the underlying genetic mechanisms. We identify two laterally transferred genes that contribute to variation in a classic example of phenotypic plasticity: the pea aphid’s ability to produce winged offspring in response to crowding. We discovered that aphid genotypes vary extensively for this trait and that aphid genes of viral origin are upregulated in response to crowding solely in highly inducible genotypes. We knocked down expression of these genes to demonstrate their functional role in wing plasticity. Through phylogenetic analysis, we found that these genes likely originated from a virus that infects rosy apple aphids and causes their hosts to produce winged offspring [3]. The function of these genes has therefore been retained following transfer to pea aphids. Our results uncover a novel role for co-opted viral genes, demonstrating that they are used to modulate ecologically relevant, plastic phenotypes. Our findings also address a critical question about the evolution of environmentally sensitive traits: whether the genes that control the expression of plastic traits also underlie variation in plasticity. The genes we identify originated from outside aphids themselves, and thus, our work shows that genes formerly unrelated to plasticity can fine-tune the strength of plastic responses to the environment.Graphical Graphical abstract for this article
  • Disassembly of Actin and Keratin Networks by Aurora B Kinase at the
           Midplane of Cleaving Xenopus laevis Eggs
    • Abstract: Publication date: Available online 6 June 2019Source: Current BiologyAuthor(s): Christine M. Field, James F. Pelletier, Timothy J. MitchisonSummaryThe large length scale of Xenopus laevis eggs facilitates observation of bulk cytoplasm dynamics far from the cortex during cytokinesis. The first furrow ingresses through the egg midplane, which is demarcated by chromosomal passenger complex (CPC) localized on microtubule bundles at the boundary between asters. Using an extract system, we found that local kinase activity of the Aurora B kinase (AURKB) subunit of the CPC caused disassembly of F-actin and keratin between asters and local softening of the cytoplasm as assayed by flow patterns. Beads coated with active CPC mimicked aster boundaries and caused AURKB-dependent disassembly of F-actin and keratin that propagated ∼40 μm without microtubules and much farther with microtubules present. Consistent with extract observations, we observed disassembly of the keratin network between asters in zygotes fixed before and during 1st cytokinesis. We propose that active CPC at aster boundaries locally reduces cytoplasmic stiffness by disassembling actin and keratin networks. Possible functions of this local disassembly include helping sister centrosomes move apart after mitosis, preparing a soft path for furrow ingression, and releasing G-actin from internal networks to build cortical networks that support furrow ingression.Graphical Graphical abstract for this article
  • Mate Selection in Self-Compatible Wild Tobacco Results from Coordinated
           Variation in Homologous Self-Incompatibility Genes
    • Abstract: Publication date: Available online 6 June 2019Source: Current BiologyAuthor(s): Han Guo, Rayko Halitschke, Natalie Wielsch, Klaus Gase, Ian T. BaldwinSummaryIn flowering plants, intraspecific mate preference is frequently related to mating systems: the rejection of self pollen in self-incompatible (SI) plants that prevents inbreeding is one of the best described examples. However, in other mating systems, more nuanced patterns of pollen rejection occur. In the self-compatible (SC) Nicotiana attenuata, in which SI is not found and all crosses are compatible, certain pollen genotypes are consistently selected in mixed pollinations. However, the molecular mechanisms of this polyandrous mate selection remain unknown. Style-expressed NaS-like-RNases and pollen-expressed NaSLF-like genes, homologous to SI factors in Solanaceae, were identified and examined for a role in N. attenuata’s mate selection. A comparison of two NaS-like-RNases and six NaSLF-like genes among 26 natural accessions revealed specific combinations of co-expression and direct protein-protein interactions. To evaluate their role in mate selection, we silenced the expression of specific NaS-like-RNases and NaSLF-like proteins and conducted diagnostic binary mixed pollinations and mixed pollinations with 14 different non-self pollen donors. Styles expressing particular combinations of NaS-like-RNases selected mates from plants with corresponding NaS-like-RNase expression patterns, while styles lacking NaS-like-RNase expression were non-selective in their fertilizations, which reflected the genotype ratios of pollen mixtures deposited on the stigmas. DNA methylation could account for some of the observed variation in stylar NaS-like-RNase patterns. We conclude that the S-RNase-SLF recognition mechanism plays a central role in polyandrous mate selection in this self-compatible species. These results suggest that after the SI-SC transition, natural variation of SI homologous genes was repurposed to mediate intraspecific mate selection.Graphical Graphical abstract for this article
  • Probing the Mechanisms of Repetition Suppression in Inferior Temporal
           Cortex with Optogenetics
    • Abstract: Publication date: Available online 6 June 2019Source: Current BiologyAuthor(s): Francesco Fabbrini, Chris Van den Haute, Marina De Vitis, Veerle Baekelandt, Wim Vanduffel, Rufin VogelsSummaryNeurons in macaque inferior temporal (IT) cortex show a decrease in the response with stimulus repetition, known as repetition suppression (RS). Several mechanisms may contribute to RS in IT, such as firing rate-dependent fatigue and transsynaptic mechanisms, like synaptic depression or reduced input from neurons within the same area or from up- or downstream areas. We examined the role of firing rate fatigue and transsynaptic mechanisms by stimulating directly IT neurons using optogenetics and measured the effect of photo-stimulation on their responses using timing parameters that resulted in RS for visual stimuli. Photo-stimulation of IT neurons resulted in a marginally decreased probability of spiking activity to a subsequent photo-stimulation or to a subsequent low-contrast visual stimulus. This response reduction was small relative to that for repeated visual stimuli and was related to post-stimulation inhibition of the activity during the interval between adapter and test stimuli. Presentation of a visual adapter did not change the response to subsequent photo-stimulation. In neurons whose response to the visual adapter was inhibited by simultaneous photo-stimulation, RS to visual stimuli was unaffected. Overall, these data imply that RS in IT has a transsynaptic origin, with little or no contribution of intrinsic firing rate fatigue. In addition, they suggest a limited contribution of both local synaptic depression and reduced input from nearby IT neurons, whose responses were postulated to be decreased by firing rate fatigue, to RS in IT.
  • Flexibility of Timescales of Evidence Evaluation for Decision Making
    • Abstract: Publication date: Available online 6 June 2019Source: Current BiologyAuthor(s): Preetham Ganupuru, Adam B. Goldring, Rashed Harun, Timothy D. HanksSummaryTo understand the neural mechanisms that support decision making, it is critical to characterize the timescale of evidence evaluation. Recent work has shown that subjects can adaptively adjust the timescale of evidence evaluation across blocks of trials depending on context [1]. However, it’s currently unknown if adjustments to evidence evaluation occur online during deliberations based on a single stream of evidence. To examine this question, we employed a change-detection task in which subjects report their level of confidence in judging whether there has been a change in a stochastic auditory stimulus. Using a combination of psychophysical reverse correlation analyses and single-trial behavioral modeling, we compared the time period over which sensory information has leverage on detection report choices versus confidence. We demonstrate that the length of this period differs on separate sets of trials based on what’s being reported. Surprisingly, confidence judgments on trials with no detection report are influenced by evidence occurring earlier than the time period of influence for detection reports. Our findings call into question models of decision formation involving static parameters that yield a singular timescale of evidence evaluation and instead suggest that the brain represents and utilizes multiple timescales of evidence evaluation during deliberation.
  • Evolution of Ovipositor Length in Drosophila suzukii Is Driven by Enhanced
           Cell Size Expansion and Anisotropic Tissue Reorganization
    • Abstract: Publication date: Available online 6 June 2019Source: Current BiologyAuthor(s): Jack E. Green, Matthieu Cavey, Emmanuelle Médina Caturegli, Benoit Aigouy, Nicolas Gompel, Benjamin Prud’hommeSummaryMorphological diversity is dominated by variation in body proportion [1], which can be described with scaling relationships and mathematical equations, following the pioneering work of D’Arcy Thompson [2] and Julian Huxley [3]. Yet, the cellular processes underlying divergence in size and shape of morphological traits between species remain largely unknown [4, 5, 6, 7, 8]. Here, we compare the ovipositors of two related species, Drosophila melanogaster and D. suzukii. D. suzukii has switched its egg-laying niche from rotting to ripe fruit [9]. Along with this shift, the D. suzukii ovipositor has undergone a significant change in size and shape [10]. Using an allometric approach, we find that, while adult ovipositor width has hardly changed between the species, D. suzukii ovipositor length is almost double that of D. melanogaster. We show that this difference mostly arises in a 6-h time window during pupal development. We observe that the developing ovipositors of the two species comprise an almost identical number of cells, with a similar profile of cell shapes and orientations. After cell division stops, we find that the ovipositor area continues to grow in both species through the isotropic expansion of cell apical area and the anisotropic cellular reorganization of the tissue. Remarkably, we find that the lengthening of the D. suzukii ovipositor compared to that of D. melanogaster results from the combination of the accelerated expansion of apical cell size and the enhanced anisotropic rearrangement of cells in the tissue. Therefore, the quantitative fine-tuning of morphogenetic processes can drive evolutionary changes in organ size and shape.Graphical Graphical abstract for this article
  • Agouti-Related Protein 2 Is a New Player in the Teleost Stress Response
    • Abstract: Publication date: Available online 6 June 2019Source: Current BiologyAuthor(s): Inbal Shainer, Maximilian Michel, Gregory D. Marquart, Ashwin A. Bhandiwad, Nilli Zmora, Zohar Ben-Moshe Livne, Yonathan Zohar, Adi Hazak, Yael Mazon, Dominique Förster, Lian Hollander-Cohen, Roger D. Cone, Harold A. Burgess, Yoav GothilfSummaryAgouti-related protein (AgRP) is a hypothalamic regulator of food consumption in mammals. However, AgRP has also been detected in circulation, but a possible endocrine role has not been examined. Zebrafish possess two agrp genes: hypothalamically expressed agrp1, considered functionally equivalent to the single mammalian agrp, and agrp2, which is expressed in pre-optic neurons and uncharacterized pineal gland cells and whose function is not well understood. By ablation of AgRP1-expressing neurons and knockout of the agrp1 gene, we show that AgRP1 stimulates food consumption in the zebrafish larvae. Single-cell sequencing of pineal agrp2-expressing cells revealed molecular resemblance to retinal-pigment epithelium cells, and anatomic analysis shows that these cells secrete peptides, possibly into the cerebrospinal fluid. Additionally, based on AgRP2 peptide localization and gene knockout analysis, we demonstrate that pre-optic AgRP2 is a neuroendocrine regulator of the stress axis that reduces cortisol secretion. We therefore suggest that the ancestral role of AgRP was functionally partitioned in zebrafish by the two AgRPs, with AgRP1 centrally regulating food consumption and AgRP2 acting as a neuroendocrine factor regulating the stress axis.
  • Figure-Ground Modulation in the Human Lateral Geniculate Nucleus Is
           Distinguishable from Top-Down Attention
    • Abstract: Publication date: Available online 6 June 2019Source: Current BiologyAuthor(s): Sonia Poltoratski, Alexander Maier, Allen T. Newton, Frank TongSummaryNearly all of the information that reaches the primary visual cortex (V1) of the brain passes from the retina through the lateral geniculate nucleus (LGN) of the thalamus. Although the LGN's role in relaying feedforward signals from the retina to the cortex is well understood [1, 2], the functional role of the extensive feedback it receives from the cortex has remained elusive [3, 4, 5, 6]. Here, we investigated whether corticothalamic feedback may contribute to perceptual processing in the LGN in a manner that is distinct from top-down effects of attention [7, 8, 9, 10]. We used high-resolution fMRI at 7 Tesla to simultaneously measure responses to orientation-defined figures in the human LGN and V1. We found robust enhancement of perceptual figures throughout the early visual system, which could be distinguished from the effects of covert spatial attention [11, 12, 13]. In a second experiment, we demonstrated that figure enhancement occurred in the LGN even when the figure and surrounding background were presented dichoptically (i.e., to different eyes). As binocular integration primarily occurs in V1 [14, 15], these results implicate a mechanism of automatic, contextually sensitive feedback from binocular visual cortex underlying figure-ground modulation in the LGN. Our findings elucidate the functional mechanisms of this core function of the visual system [16, 17, 18], which allows people to segment and detect meaningful figures in complex visual environments. The involvement of the LGN in this rich, contextually informed visual processing—despite showing minimal feedforward selectivity for visual features [19, 20]—underscores the role of recurrent processing at the earliest stages of visual processing.
  • Ancient Mitogenomes Reveal the Evolutionary History and Biogeography of
    • Abstract: Publication date: Available online 6 June 2019Source: Current BiologyAuthor(s): Frédéric Delsuc, Melanie Kuch, Gillian C. Gibb, Emil Karpinski, Dirk Hackenberger, Paul Szpak, Jorge G. Martínez, Jim I. Mead, H. Gregory McDonald, Ross D.E. MacPhee, Guillaume Billet, Lionel Hautier, Hendrik N. PoinarSummaryLiving sloths represent two distinct lineages of small-sized mammals that independently evolved arboreality from terrestrial ancestors. The six extant species are the survivors of an evolutionary radiation marked by the extinction of large terrestrial forms at the end of the Quaternary. Until now, sloth evolutionary history has mainly been reconstructed from phylogenetic analyses of morphological characters. Here, we used ancient DNA methods to successfully sequence 10 extinct sloth mitogenomes encompassing all major lineages. This includes the iconic continental ground sloths Megatherium, Megalonyx, Mylodon, and Nothrotheriops and the smaller endemic Caribbean sloths Parocnus and Acratocnus. Phylogenetic analyses identify eight distinct lineages grouped in three well-supported clades, whose interrelationships are markedly incongruent with the currently accepted morphological topology. We show that recently extinct Caribbean sloths have a single origin but comprise two highly divergent lineages that are not directly related to living two-fingered sloths, which instead group with Mylodon. Moreover, living three-fingered sloths do not represent the sister group to all other sloths but are nested within a clade of extinct ground sloths including Megatherium, Megalonyx, and Nothrotheriops. Molecular dating also reveals that the eight newly recognized sloth families all originated between 36 and 28 million years ago (mya). The early divergence of recently extinct Caribbean sloths around 35 mya is consistent with the debated GAARlandia hypothesis postulating the existence at that time of a biogeographic connection between northern South America and the Greater Antilles. This new molecular phylogeny has major implications for reinterpreting sloth morphological evolution, biogeography, and diversification history.Graphical Graphical abstract for this article
  • Sponges as natural environmental DNA samplers
    • Abstract: Publication date: 3 June 2019Source: Current Biology, Volume 29, Issue 11Author(s): Stefano Mariani, Charles Baillie, Giuliano Colosimo, Ana RiesgoSummaryAt a time of unprecedented impacts on marine biodiversity, scientists are rapidly becoming persuaded by the potential of screening large swathes of the oceans through the retrieval, amplification and sequencing of trace DNA fragments left behind by marine organisms; an approach known as ‘environmental DNA’ (eDNA) [1]. In trying to circumvent the many challenges associated with water filtration and DNA isolation from environmental samples, significant investment is being made in high-tech solutions, such as automated underwater vehicles and robots [2]. Here, instead, we explored a simpler, alternative option, based on the recovery of eDNA from sponges (phylum Porifera), the planet’s most effective water-filterers. We obtained sponge samples from Mediterranean and Antarctic surveys, extracted total DNA from their tissues, and obtained tens of thousands of fish DNA reads via metabarcoding, which were able to clearly distinguish samples from the two regions. One Antarctic sample yielded hundreds of reads from chinstrap penguin (Pygoscelis antarcticus) and Weddell seal (Leptonychotes weddellii). We argue that this ‘natural sampler DNA’ (nsDNA) approach is poised to become a powerful, affordable, universal tool for aquatic biodiversity monitoring globally.
  • Drivers of Spatial Structure in Social Microbial Communities
    • Abstract: Publication date: 3 June 2019Source: Current Biology, Volume 29, Issue 11Author(s): David Yanni, Pedro Márquez-Zacarías, Peter J. Yunker, William C. RatcliffMicrobes are social organisms, interacting primarily through secreted biomolecules. Many traits have evolved based solely on their effects upon other community members, yet even individually beneficial traits often create social side effects that are mediated by spatial population structure. Predicting the evolution of many microbial traits thus requires a comprehensive understanding of their social consequences. In this review, we examine the critical role of population spatial structure in microbial social evolution. We briefly review key mechanisms structuring microbial communities, focusing primarily on the universal roles of cellular death and reproduction. Finally, we explain how spatial assortment can be efficiently calculated in two-dimensional, surface-attached populations.
  • Understanding Competition and Cooperation within the Mammalian Gut
    • Abstract: Publication date: 3 June 2019Source: Current Biology, Volume 29, Issue 11Author(s): Katharine Z. Coyte, Seth Rakoff-NahoumThe mammalian gut harbors a vast community of microorganisms — termed the microbiota — whose composition and dynamics are considered to be critical drivers of host health. These factors depend, in part, upon the manner in which microbes interact with one another. Microbes are known to engage in a myriad of different ways, ranging from unprovoked aggression to actively feeding each other. However, the relative extent to which these different interactions occur between microbes within the gut is unclear. In this minireview we assess our current knowledge of microbe–microbe interactions within the mammalian gut microbiota, and the array of methods used to uncover them. In particular, we highlight the discrepancies between different methodologies: some studies have revealed rich networks of cross-feeding interactions between microbes, whereas others suggest that microbes are more typically locked in conflict and actively cooperate only rarely. We argue that to reconcile these contradictions we must recognize that interactions between members of the microbiota can vary across condition, space, and time — and that only through embracing this dynamism will we be able to comprehensively understand the ecology of our gut communities.
  • The Evolution and Ecology of Bacterial Warfare
    • Abstract: Publication date: 3 June 2019Source: Current Biology, Volume 29, Issue 11Author(s): Elisa T. Granato, Thomas A. Meiller-Legrand, Kevin R. FosterBacteria have evolved a wide range of mechanisms to harm and kill their competitors, including chemical, mechanical and biological weapons. Here we review the incredible diversity of bacterial weapon systems, which comprise antibiotics, toxic proteins, mechanical weapons that stab and pierce, viruses, and more. The evolution of bacterial weapons is shaped by many factors, including cell density and nutrient abundance, and how strains are arranged in space. Bacteria also employ a diverse range of combat behaviours, including pre-emptive attacks, suicidal attacks, and reciprocation (tit-for-tat). However, why bacteria carry so many weapons, and why they are so often used, remains poorly understood. By comparison with animals, we argue that the way that bacteria live — often in dense and genetically diverse communities — is likely to be key to their aggression as it encourages them to dig in and fight alongside their clonemates. The intensity of bacterial aggression is such that it can strongly affect communities, via complex coevolutionary and eco-evolutionary dynamics, which influence species over space and time. Bacterial warfare is a fascinating topic for ecology and evolution, as well as one of increasing relevance. Understanding how bacteria win wars is important for the goal of manipulating the human microbiome and other important microbial systems.
  • Fertility Costs of Meiotic Drivers
    • Abstract: Publication date: 3 June 2019Source: Current Biology, Volume 29, Issue 11Author(s): Sarah E. Zanders, Robert L. UncklessIn sexual reproduction, opportunities are limited and the stakes are high. This inevitably leads to conflict. One pervasive conflict occurs within genomes between alternative alleles at heterozygous loci. Each gamete and thus each offspring will inherit only one of the two alleles from a heterozygous parent. Most alleles ‘play fair’ and have a 50% chance of being included in any given gamete. However, alleles can gain an enormous advantage if they act selfishly to force their own transmission into more than half, sometimes even all, of the functional gametes. These selfish alleles are known as ‘meiotic drivers’, and their cheating often incurs a high cost on the fertility of eukaryotes ranging from plants to mammals. Here, we review how several types of meiotic drivers directly and indirectly contribute to infertility, and argue that a complete picture of the genetics of infertility will require focusing on both the standard alleles — those that play fair — as well as selfish alleles involved in genetic conflict.
  • Selfish Mitonuclear Conflict
    • Abstract: Publication date: 3 June 2019Source: Current Biology, Volume 29, Issue 11Author(s): Justin C. Havird, Evan S. Forsythe, Alissa M. Williams, John H. Werren, Damian K. Dowling, Daniel B. SloanMitochondria, a nearly ubiquitous feature of eukaryotes, are derived from an ancient symbiosis. Despite billions of years of cooperative coevolution — in what is arguably the most important mutualism in the history of life — the persistence of mitochondrial genomes also creates conditions for genetic conflict with the nucleus. Because mitochondrial genomes are present in numerous copies per cell, they are subject to both within- and among-organism levels of selection. Accordingly, ‘selfish’ genotypes that increase their own proliferation can rise to high frequencies even if they decrease organismal fitness. It has been argued that uniparental (often maternal) inheritance of cytoplasmic genomes evolved to curtail such selfish replication by minimizing within-individual variation and, hence, within-individual selection. However, uniparental inheritance creates conditions for cytonuclear conflict over sex determination and sex ratio, as well as conditions for sexual antagonism when mitochondrial variants increase transmission by enhancing maternal fitness but have the side-effect of being harmful to males (i.e., ‘mother’s curse’). Here, we review recent advances in understanding selfish replication and sexual antagonism in the evolution of mitochondrial genomes and the mechanisms that suppress selfish interactions, drawing parallels and contrasts with other organelles (plastids) and bacterial endosymbionts that arose more recently. Although cytonuclear conflict is widespread across eukaryotes, it can be cryptic due to nuclear suppression, highly variable, and lineage-specific, reflecting the diverse biology of eukaryotes and the varying architectures of their cytoplasmic genomes.
  • The Life of an Insect Endosymbiont from the Cradle to the Grave
    • Abstract: Publication date: 3 June 2019Source: Current Biology, Volume 29, Issue 11Author(s): John P. McCutcheon, Bret M. Boyd, Colin DaleHost-beneficial endosymbioses, which are formed when a microorganism takes up residence inside another cell and provides a fitness advantage to the host, have had a dramatic influence on the evolution of life. These intimate relationships have yielded the mitochondrion and the plastid (chloroplast) — the ancient organelles that in part define eukaryotic life — along with many more recent associations involving a wide variety of hosts and microbial partners. These relationships are often envisioned as stable associations that appear cooperative and persist for extremely long periods of time. But recent evidence suggests that this stable state is often born from turbulent and conflicting origins, and that the apparent stability of many beneficial endosymbiotic relationships — although certainly real in many cases — is not an inevitable outcome of these associations. Here we review how stable endosymbioses form, how they are maintained, and how they sometimes break down and are reborn. We focus on relationships formed by insects and their resident microorganisms because these symbioses have been the focus of significant empirical work over the last two decades. We review these relationships over five life stages: origin, birth, middle age, old age, and death.
  • Enforcing Cooperation in the Social Amoebae
    • Abstract: Publication date: 3 June 2019Source: Current Biology, Volume 29, Issue 11Author(s): Elizabeth A. OstrowskiCooperation has been essential to the evolution of biological complexity, but many societies struggle to overcome internal conflicts and divisions. Dictyostelium discoideum, or the social amoeba, has been a useful model system for exploring these conflicts and how they can be resolved. When starved, these cells communicate, gather into groups, and build themselves into a multicellular fruiting body. Some cells altruistically die to form the rigid stalk, while the remainder sit atop the stalk, become spores, and disperse. Evolutionary theory predicts that conflict will arise over which cells die to form the stalk and which cells become spores and survive. The power of the social amoeba lies in the ability to explore how cooperation and conflict work across multiple levels, ranging from proximate mechanisms (how does it work') to ultimate evolutionary answers (why does it work'). Recent studies point to solutions to the problem of ensuring fairness, such as the ability to suppress selfishness and to recognize and avoid unrelated individuals. This work confirms a central role for kin selection, but also suggests new explanations for how social amoebae might enforce cooperation. New approaches based on genomics are also enabling researchers to decipher for the first time the evolutionary history of cooperation and conflict and to determine its role in shaping the biology of multicellular organisms.
  • Cooperation in children
    • Abstract: Publication date: 3 June 2019Source: Current Biology, Volume 29, Issue 11Author(s): Katie E. Slocombe, Amanda M. SeedCooperation is central to what makes us human. It is so deeply entrenched in our nature that it can be seen at the heart of every culture, whether it takes the form of group hunting, shared child-rearing, or large-scale, multi-national institutions such as the UN. And yet in contrast to the constancy of other forms of cooperation in non-human animals, such as termite-mound building or honey bee dancing, the changing face of human cooperation makes it seem more fragile, and its mechanisms more elusive. As with other features of our behaviour, human cooperation is the product of both genetic and cultural evolution. Studying cooperation in children, in different cultural environments, and in contrast to other species, provides a valuable window into the ways in which these two forms of inheritance interact over development, and a chance to distil out its constitutive components.
  • Mutualism and biodiversity
    • Abstract: Publication date: 3 June 2019Source: Current Biology, Volume 29, Issue 11Author(s): Jordi BascompteMutualism is a type of interaction in which both partners benefit from each other. For example, a butterfly receives nectar, a rich source of food, from the flower of a plant and in turn moves pollen from that plant to another far away (Figure 1). In order to reflect about the widespread nature of mutualism, John N. Thompson proposed the following thought experiment: try to imagine a plant species that is viable in its natural habitat without using on top of its own nuclear genome the genomes of a mitochondrion, a chloroplast, of several mycorrhizal fungi, of several insects to pollinate it and of several species of bird to disperse its seeds. Mutualism is everywhere and it is assumed that mutualistic interactions have played a major role in the diversification of life on Earth. An often-cited example is the rich adaptive radiation of the flowering plants (angiosperms), with about 300,000 described species. Flowering plants originated around 160 million years ago and diversified fast during the Early Cretaceous, so that by around 120 million years ago they had become widespread. It is generally assumed that such a fast diversification is largely the result of the mutualistic interaction with pollinators. Thus, mutualism has been most likely shaping the diversity of species on Earth from an early stage. But the relationships between mutualism and diversity are not yet clear, mainly because mutualism has traditionally been studied within pairs or small groups of species. Also, mutualism has historically been studied in isolation from competition, so it is unclear how these two forces balance each other in ecological communities.
  • Invertebrate allorecognition
    • Abstract: Publication date: 3 June 2019Source: Current Biology, Volume 29, Issue 11Author(s): Matthew L. NicotraMost colonial marine invertebrates live as surface encrustations in benthic environments. As they grow, these animals frequently encounter other members of their own species. These encounters typically lead to conflict, in which the colonies aggressively compete for space, or co-existence, in which the colonies peacefully border each other. Sometimes, however, interacting colonies will engage in a form of cooperation in which they fuse together and actively share resources.
  • Social immunity in insects
    • Abstract: Publication date: 3 June 2019Source: Current Biology, Volume 29, Issue 11Author(s): Sylvia CremerWhen animals become sick, infected cells and an armada of activated immune cells attempt to eliminate the pathogen from the body. Once infectious particles have breached the body’s physical barriers of the skin or gut lining, an initially local response quickly escalates into a systemic response, attracting mobile immune cells to the site of infection. These cells complement the initial, unspecific defense with a more specialized, targeted response. This can also provide long-term immune memory and protection against future infection. The cell-autonomous defenses of the infected cells are thus aided by the actions of recruited immune cells. These specialized cells are the most mobile cells in the body, constantly patrolling through the otherwise static tissue to detect incoming pathogens. Such constant immune surveillance means infections are noticed immediately and can be rapidly cleared from the body. Some immune cells also remove infected cells that have succumbed to infection. All this prevents pathogen replication and spread to healthy tissues. Although this may involve the sacrifice of some somatic tissue, this is typically replaced quickly. Particular care is, however, given to the reproductive organs, which should always remain disease free (immune privilege).
  • Cooperation and conflict in human pregnancy
    • Abstract: Publication date: 3 June 2019Source: Current Biology, Volume 29, Issue 11Author(s): David HaigFor many humans living today, obstetric care begins early in pregnancy, and most babies are born in hospitals. These are precautionary measures. Medical complications during the brief nine months of pregnancy are such a common part of human experience that we rarely ask ourselves why gestation does not always proceed as smoothly and reliably as the lifelong beating of our heart or filtration of blood by our kidneys. The birth of a healthy child is central to reproductive fitness and must have been subject to strong natural selection. Why then should placentas be less reliable organs than hearts or kidneys' Why should maternal hearts and kidneys be more subject to catastrophic failures during pregnancy than at other times' A crucial contrast distinguishes obstetrics from cardiology and nephrology. The coordinated activities of heart and kidneys take place within an individual comprised of genetically largely identical cells, whereas pregnancy involves an interaction between genetically-distinct individuals whose cooperation is obviated by evolutionary conflicts of interest.
  • Sexual conflict
    • Abstract: Publication date: 3 June 2019Source: Current Biology, Volume 29, Issue 11Author(s): David J. Hosken, C. Ruth Archer, Judith E. MankEvolutionary conflict arises from differences in the fitness interests of replicating entities and has its roots in relatedness asymmetries. Every replicator is related to itself by 100%, but in most cases is less related to other replicators, which generates selfishness and conflicts of interest. Since this basic condition is the norm at many levels of biological organization, conflict is rife in biological systems. Sexual conflict, on which we focus here, is the evolutionary conflict that occurs between males and females because of their divergent fitness interests. Sexual conflict occurs despite sexual reproduction requiring some level of cooperation between males and females because the fitness interests of the sexes are nevertheless never perfectly aligned. In other words, males and females may agree on where they are going, but not necessarily on how to get there. Sexual conflict is a vast topic with relevance to many areas of biology and so here we restrict our focus to matters we think are of broadest interest.
  • The evolution of human cooperation
    • Abstract: Publication date: 3 June 2019Source: Current Biology, Volume 29, Issue 11Author(s): Coren L. Apicella, Joan B. SilkDarwin viewed cooperation as a perplexing challenge to his theory of natural selection. Natural selection generally favors the evolution of behaviors that enhance the fitness of individuals. Cooperative behavior, which increases the fitness of a recipient at the expense of the donor, contradicts this logic. William D. Hamilton helped to solve the puzzle when he showed that cooperation can evolve if cooperators direct benefits selectively to other cooperators (i.e. assortment). Kinship, group selection and the previous behavior of social partners all provide mechanisms for assortment (Figure 1), and kin selection and reciprocal altruism are the foundation of the kinds of cooperative behavior observed in many animals. Humans also bias cooperation in favor of kin and reciprocating partners, but the scope, scale, and variability of human cooperation greatly exceed that of other animals. Here, we introduce derived features of human cooperation in the context in which they originally evolved, and discuss the processes that may have shaped the evolution of our remarkable capacity for cooperation. We argue that culturally-evolved norms that specify how people should behave provide an evolutionarily novel mechanism for assortment, and play an important role in sustaining derived properties of cooperation in human groups.
  • Public goods and cheating in microbes
    • Abstract: Publication date: 3 June 2019Source: Current Biology, Volume 29, Issue 11Author(s): Parker Smith, Martin SchusterCommunication and cooperation are not restricted to complex, higher organisms. Microbes, too, perform a variety of collective, multicellular behaviors, including biofilm formation, quorum sensing, nutrient acquisition, and dispersal. The products of these microbial cooperative behaviors are generally referred to as public goods. Here we describe the nature of microbial public goods, the associated problem of cheating, and ways in which microbes maintain public goods in the face of cheating. We highlight work in a growing field at the interface of microbiology, evolution, and ecology that combines multiple approaches in experimental evolution, genetics, and mathematical modeling.
  • Kin selection and altruism
    • Abstract: Publication date: 3 June 2019Source: Current Biology, Volume 29, Issue 11Author(s): Tomas Kay, Laurent Lehmann, Laurent KellerNatural selection is predicated on the ‘struggle for existence’: life is short, cruel and, whether through predation, disease or starvation, often ends traumatically. It would seem that in such a dog-eat-dog world, organisms ought to act selfishly, and avoid reducing their fitness (expected survival and reproductive success) by expending time and energy helping others. Put another way, alleles that increase the probability of altruism — a behavior whose expression increases the fitness of recipients while decreasing that of the actor — should decrease in frequency across generations and ultimately disappear.
  • Are kin and group selection rivals or friends'
    • Abstract: Publication date: 3 June 2019Source: Current Biology, Volume 29, Issue 11Author(s): Jonathan BirchKin selection and group selection were once seen as competing explanatory hypotheses but now tend to be seen as equivalent ways of describing the same basic idea. Yet this ‘equivalence thesis’ seems not to have brought proponents of kin selection and group selection any closer together. This may be because the equivalence thesis merely shows the equivalence of two statistical formalisms without saying anything about causality. W.D. Hamilton was the first to derive an equivalence result of this type. Yet Hamilton was aware of its limitations, and saw that, while illuminating, it papered over some biologically important distinctions. Attending to these distinctions leads to the concept of ‘K-G space’, which helps us see where the biological disagreements between proponents of kin selection and group selection really lie.
  • Policing
    • Abstract: Publication date: 3 June 2019Source: Current Biology, Volume 29, Issue 11Author(s): Ashleigh Griffin
  • The greenbeard effect
    • Abstract: Publication date: 3 June 2019Source: Current Biology, Volume 29, Issue 11Author(s): Andy Gardner
  • Uncovering the roots of religion
    • Abstract: Publication date: 3 June 2019Source: Current Biology, Volume 29, Issue 11Author(s): Michael GrossSummaryReligious beliefs can inspire collaboration on enormous scales, as witnessed by monuments like ancient cathedrals and mosques. At the same time, they are also known to fuel conflicts which haunt us to this day. The most powerful and pervasive ‘big god’ beliefs appear to be a relatively late-occurring phenomenon in the evolution of complex societies, as a comprehensive new study suggests. Michael Gross reports.
  • Conflict within cooperation
    • Abstract: Publication date: 3 June 2019Source: Current Biology, Volume 29, Issue 11Author(s): Stuart A. West, Melanie Ghoul
  • Gene Regulation: Analog to Digital Conversion of Transcription Factor
    • Abstract: Publication date: 3 June 2019Source: Current Biology, Volume 29, Issue 11Author(s): Dimitrios K. Papadopoulos, Pavel TomancakTranscription factor gradients trigger differential transcriptional responses based on concentration. But how, in some cases, do target genes maintain uniform transcription across portions of the gradient' Lessons from Drosophila demonstrate that organization of transcription into ‘hubs’ can lead to local increases in transcription factor concentration.
  • Developmental Timing: Honey, I Reprogrammed the Kids
    • Abstract: Publication date: 3 June 2019Source: Current Biology, Volume 29, Issue 11Author(s): Adam AntebiA new study finds that signaling pathways promoting developmental quiescence can reprogram developmental time.
  • Dietary Evolution: The Panda Paradox
    • Abstract: Publication date: 3 June 2019Source: Current Biology, Volume 29, Issue 11Author(s): Matt Sponheimer, Marcus Clauss, Daryl CodronGiant pandas are specialized herbivores that digest little of the bamboo they consume. A new study argues that pandas, like carnivores, get most of their energy from protein, explaining their carnivore-like guts and poor digestion. This may have facilitated their ancestors’ transition to herbivory.
  • Evolution: Environmental Dependence of the Mutational Process
    • Abstract: Publication date: 3 June 2019Source: Current Biology, Volume 29, Issue 11Author(s): Charles F. BaerEnvironmental dependence of mutation in microbes is well-known, but most experiments have investigated contexts in which growth rate is greatly reduced below optimum. A new experiment shows mutational variability extends to contexts in which growth is near optimum.
  • Evolution: Bedbugs Evolved before Their Assumed Ancestral Host
    • Abstract: Publication date: 3 June 2019Source: Current Biology, Volume 29, Issue 11Author(s): Warren BoothIt has long been assumed that human-parasitic bedbugs evolved from the ectoparasites of bats. However, new fossil-calibrated phylogenetic analysis places their appearance at ∼115 million years ago; before the Cretaceous–Paleogene mass extinction and ∼30 million years prior to fossil records of the first bats.
  • Coastal Ecology: Living Shorelines Reduce Coastal Erosion
    • Abstract: Publication date: 3 June 2019Source: Current Biology, Volume 29, Issue 11Author(s): Delbert Lee SmeeBenefits derived from natural ecosystems are commonly mentioned as justification for protecting and restoring habitats, yet measuring these services can be challenging. New research quantitatively assessed an ecosystem service provided by coastal marshes and revealed that removal of smooth cordgrass significantly increased coastal erosion, clearly demonstrating that marshes protect shorelines.
  • Motor Evolution: Lit-Up Hydra Bare All
    • Abstract: Publication date: 3 June 2019Source: Current Biology, Volume 29, Issue 11Author(s): Scott L. HooperWhole-animal Hydra imaging shows that epitheliomuscular calcium influx dynamics and inter-cell progression speeds are very different for different behaviors. Hydra movements therefore likely arise from fast (ionotropic) and slow (metabotropic) neural mechanisms, and from interactions among the epitheliomuscular cells themselves.
  • Plant Cell Biology: How to Give Root Hairs Enough ROPs'
    • Abstract: Publication date: 3 June 2019Source: Current Biology, Volume 29, Issue 11Author(s): Thomas Stanislas, Yvon JaillaisRoot hairs are precisely positioned close to the rootward end of epidermal cells. A new study shows that the successful production of root hairs is a two-step process with different molecular players driving the initial cell polarization and subsequent hair outgrowth.
  • Infrared Imaging: A Motion Detection Circuit for Rattlesnake Thermal
    • Abstract: Publication date: 3 June 2019Source: Current Biology, Volume 29, Issue 11Author(s): Almut KelberPit vipers detect moving warm-blooded prey with infrared receptors in their pit organs. Neurons in two brain nuclei extract the direction of prey motion by lateral inhibition circuits similar to those known from visual systems.
  • γ-TuRCs
    • Abstract: Publication date: 3 June 2019Source: Current Biology, Volume 29, Issue 11Author(s): Amrita Mukherjee, Paul T. Conduit
  • Petra Anne Levin
    • Abstract: Publication date: 3 June 2019Source: Current Biology, Volume 29, Issue 11Author(s): Petra Anne Levin
  • Luminary Lasker laureates of Chinese descent
    • Abstract: Publication date: 3 June 2019Source: Current Biology, Volume 29, Issue 11Author(s): Alfred C. Chin
  • Cryptochromes-Mediated Inhibition of the CRL4Cop1-Complex Assembly Defines
           an Evolutionary Conserved Signaling Mechanism
    • Abstract: Publication date: Available online 30 May 2019Source: Current BiologyAuthor(s): Luca Rizzini, Daniel C. Levine, Mark Perelis, Joseph Bass, Clara B. Peek, Michele PaganoSummaryIn plants, cryptochromes are photoreceptors that negatively regulate the ubiquitin ligase CRL4Cop1. In mammals, cryptochromes are core components of the circadian clock and repressors of the glucocorticoid receptor (GR). Moreover, mammalian cryptochromes lost their ability to interact with Cop1, suggesting that they are unable to inhibit CRL4Cop1. Contrary to this assumption, we found that mammalian cryptochromes are also negative regulators of CRL4Cop1, and through this mechanism, they repress the GR transcriptional network both in cultured cells and in the mouse liver. Mechanistically, cryptochromes inactivate Cop1 by interacting with Det1, a subunit of the mammalian CRL4Cop1 complex that is not present in other CRL4s. Through this interaction, the ability of Cop1 to join the CRL4 complex is inhibited; therefore, its substrates accumulate. Thus, the interaction between cryptochromes and Det1 in mammals mirrors the interaction between cryptochromes and Cop1 in planta, pointing to a common ancestor in which the cryptochromes-Cop1 axis originated.Graphical Graphical abstract for this article
  • Olfactory and Neuromodulatory Signals Reverse Visual Object Avoidance to
           Approach in Drosophila
    • Abstract: Publication date: Available online 30 May 2019Source: Current BiologyAuthor(s): Karen Y. Cheng, Rachel A. Colbath, Mark A. FryeSummaryBehavioral reactions of animals to environmental sensory stimuli are sometimes reflexive and stereotyped but can also vary depending on contextual conditions. Engaging in active foraging or flight provokes a reversal in the valence of carbon dioxide responses from aversion to approach in Drosophila [1, 2], whereas mosquitoes encountering this same chemical cue show enhanced approach toward a small visual object [3]. Sensory plasticity in insects has been broadly attributed to the action of biogenic amines, which modulate behaviors such as olfactory learning, aggression, feeding, and egg laying [4, 5, 6, 7, 8, 9, 10, 11, 12, 13, 14]. Octopamine acts rapidly upon the onset of flight to modulate the response gain of directionally selective motion-detecting neurons in Drosophila [15]. How the action of biogenic amines might couple sensory modalities to each other or to locomotive states remains poorly understood. Here, we use a visual flight simulator [16] equipped for odor delivery [17] to confirm that flies avoid a small contrasting visual object in odorless air [18] but that the same animals reverse their preference to approach in the presence of attractive food odor. An aversive odor does not reverse object aversion. Optogenetic activation of either octopaminergic neurons or directionally selective motion-detecting neurons that express octopamine receptors elicits visual valence reversal in the absence of odor. Our results suggest a parsimonious model in which odor-activated octopamine release excites the motion detection pathway to increase the saliency of either a small object or a bar, eliciting tracking responses by both visual features.
  • Opposing Effects of Growth and Differentiation Factors in Cell-Fate
    • Abstract: Publication date: Available online 30 May 2019Source: Current BiologyAuthor(s): Kun-Che Chang, Catalina Sun, Evan G. Cameron, Ankush Madaan, Suqian Wu, Xin Xia, Xiong Zhang, Kevin Tenerelli, Michael Nahmou, Cara M. Knasel, Kristina R. Russano, Jonathan Hertz, Jeffrey L. GoldbergSummaryFollowing ocular trauma or in diseases such as glaucoma, irreversible vision loss is due to the death of retinal ganglion cell (RGC) neurons. Although strategies to replace these lost cells include stem cell replacement therapy, few differentiated stem cells turn into RGC-like neurons. Understanding the regulatory mechanisms of RGC differentiation in vivo may improve outcomes of cell transplantation by directing the fate of undifferentiated cells toward mature RGCs. Here, we report a new mechanism by which growth and differentiation factor-15 (GDF-15), a ligand in the transforming growth factor-beta (TGF-β) superfamily, strongly promotes RGC differentiation in the developing retina in vivo in rodent retinal progenitor cells (RPCs) and in human embryonic stem cells (hESCs). This effect is in direct contrast to the closely related ligand GDF-11, which suppresses RGC-fate specification. We find these opposing effects are due in part to GDF-15’s ability to specifically suppress Smad-2, but not Smad-1, signaling induced by GDF-11, which can be recapitulated by pharmacologic or genetic blockade of Smad-2 in vivo to increase RGC specification. No other retinal cell types were affected by GDF-11 knockout, but a slight reduction in photoreceptor cells was observed by GDF-15 knockout in the developing retina in vivo. These data define a novel regulatory mechanism of GDFs’ opposing effects and their relevance in RGC differentiation and suggest a potential approach for advancing ESC-to-RGC cell-based replacement therapies.Graphical Graphical abstract for this article
  • An Analysis of Decision under Risk in Rats
    • Abstract: Publication date: Available online 30 May 2019Source: Current BiologyAuthor(s): Christine M. Constantinople, Alex T. Piet, Carlos D. BrodySummaryIn 1979, Daniel Kahneman and Amos Tversky published a ground-breaking paper titled “Prospect Theory: An Analysis of Decision under Risk,” which presented a behavioral economic theory that accounted for the ways in which humans deviate from economists’ normative workhorse model, Expected Utility Theory [1, 2]. For example, people exhibit probability distortion (they overweight low probabilities), loss aversion (losses loom larger than gains), and reference dependence (outcomes are evaluated as gains or losses relative to an internal reference point). We found that rats exhibited many of these same biases, using a task in which rats chose between guaranteed and probabilistic rewards. However, prospect theory assumes stable preferences in the absence of learning, an assumption at odds with alternative frameworks such as animal learning theory and reinforcement learning [3, 4, 5, 6, 7]. Rats also exhibited trial history effects, consistent with ongoing learning. A reinforcement learning model in which state-action values were updated by the subjective value of outcomes according to prospect theory reproduced rats’ nonlinear utility and probability weighting functions and also captured trial-by-trial learning dynamics.
  • Regulated Activation of the PAR Polarity Network Ensures a Timely and
           Specific Response to Spatial Cues
    • Abstract: Publication date: Available online 30 May 2019Source: Current BiologyAuthor(s): Jacob D. Reich, Lars Hubatsch, Rukshala Illukkumbura, Florent Peglion, Tom Bland, Nisha Hirani, Nathan W. GoehringSummaryHow do cells polarize at the correct time and in response to the correct cues? In the C. elegans zygote, the timing and geometry of polarization rely on a single dominant cue—the sperm centrosome—that matures at the end of meiosis and specifies the nascent posterior. Polarization requires that the conserved PAR proteins, which specify polarity in the zygote, be poised to respond to the centrosome. Yet, how and when PAR proteins achieve this unpolarized, but responsive, state is unknown. We show that oocyte maturation initiates a fertilization-independent PAR activation program. PAR proteins are initially not competent to polarize but gradually acquire this ability following oocyte maturation. Surprisingly, this program allows symmetry breaking even in unfertilized oocytes lacking centrosomes. Thus, if PAR proteins can respond to multiple polarizing cues, how is specificity for the centrosome achieved? Specificity is enforced by Polo-like and Aurora kinases (PLK-1 and AIR-1 in C. elegans), which impose a delay in the activation of the PAR network so that it coincides with maturation of the centrosome cue. This delay suppresses polarization by non-centrosomal cues, which can otherwise trigger premature polarization and multiple or reversed polarity domains. Taken together, these findings identify a regulatory program that enforces proper polarization by synchronizing PAR network activation with cell cycle progression, thereby ensuring that PAR proteins respond specifically to the correct cue. Temporal control of polarity network activity is likely to be a common strategy to ensure robust, dynamic, and specific polarization in response to developmentally deployed cues.Graphical Graphical abstract for this article
  • Dynamic REM Sleep Modulation by Ambient Temperature and the Critical Role
           of the Melanin-Concentrating Hormone System
    • Abstract: Publication date: Available online 30 May 2019Source: Current BiologyAuthor(s): Noëmie Komagata, Blerina Latifi, Thomas Rusterholz, Claudio L.A. Bassetti, Antoine Adamantidis, Markus H. SchmidtSummaryAmbient temperature (Ta) warming toward the high end of the thermoneutral zone (TNZ) preferentially increases rapid eye movement (REM) sleep over non-REM (NREM) sleep across species. The control and function of this temperature-induced REM sleep expression have remained unknown. Melanin-concentrating hormone (MCH) neurons play an important role in REM sleep control. We hypothesize that the MCH system may modulate REM sleep as a function of Ta. Here, we show that wild-type (WT) mice dynamically increased REM sleep durations specifically during warm Ta pulsing within the TNZ, compared to both the TNZ cool and baseline constant Ta conditions, without significantly affecting either wake or NREM sleep durations. However, genetically engineered MCH receptor-1 knockout (MCHR1-KO) mice showed no significant changes in REM sleep as a function of Ta, even with increased sleep pressure following a 4-h sleep deprivation. Using MCH-cre mice transduced with channelrhodopsin, we then optogenetically activated MCH neurons time locked with Ta warming, showing an increase in REM sleep expression beyond what Ta warming in yellow fluorescent protein (YFP) control mice achieved. Finally, in mice transduced with archaerhodopsin-T, semi-chronic optogenetic MCH neuronal silencing during Ta warming completely blocked the increase in REM sleep seen in YFP controls. These data demonstrate a previously unknown role for the MCH system in the dynamic output expression of REM sleep during Ta manipulation. These findings are consistent with the energy allocation hypothesis of sleep function, suggesting that endotherms have evolved neural circuits to opportunistically express REM sleep when the need for thermoregulatory defense is minimized.Graphical Graphical abstract for this article
  • Cell Boundary Confinement Sets the Size and Position of the
           E. coli Chromosome
    • Abstract: Publication date: Available online 30 May 2019Source: Current BiologyAuthor(s): Fabai Wu, Pinaki Swain, Louis Kuijpers, Xuan Zheng, Kevin Felter, Margot Guurink, Jacopo Solari, Suckjoon Jun, Thomas S. Shimizu, Debasish Chaudhuri, Bela Mulder, Cees DekkerSummaryAlthough the spatiotemporal structure of the genome is crucial to its biological function, many basic questions remain unanswered on the morphology and segregation of chromosomes. Here, we experimentally show in Escherichia coli that spatial confinement plays a dominant role in determining both the chromosome size and position. In non-dividing cells with lengths increased to 10 times normal, single chromosomes are observed to expand> 4-fold in size. Chromosomes show pronounced internal dynamics but exhibit a robust positioning where single nucleoids reside robustly at mid-cell, whereas two nucleoids self-organize at 1/4 and 3/4 positions. The cell-size-dependent expansion of the nucleoid is only modestly influenced by deletions of nucleoid-associated proteins, whereas osmotic manipulation experiments reveal a prominent role of molecular crowding. Molecular dynamics simulations with model chromosomes and crowders recapitulate the observed phenomena and highlight the role of entropic effects caused by confinement and molecular crowding in the spatial organization of the chromosome.Graphical Graphical abstract for this article
  • Reproductive Capacity Evolves in Response to Ecology through Common
           Changes in Cell Number in Hawaiian Drosophila
    • Abstract: Publication date: Available online 23 May 2019Source: Current BiologyAuthor(s): Didem P. Sarikaya, Samuel H. Church, Laura P. Lagomarsino, Karl N. Magnacca, Steven L. Montgomery, Donald K. Price, Kenneth Y. Kaneshiro, Cassandra G. ExtavourSummaryLifetime reproductive capacity is a critical fitness component. In insects, female reproductive capacity is largely determined by the number of ovarioles, the egg-producing subunits of the ovary [e.g., 1]. Recent work has provided insights into ovariole number regulation in Drosophila melanogaster. However, whether mechanisms discovered under laboratory conditions explain evolutionary variation in natural populations is an outstanding question. We investigated potential effects of ecology on the developmental processes underlying ovariole number evolution among Hawaiian Drosophila, a large adaptive radiation wherein the highest and lowest ovariole numbers of the family have evolved within 25 million years. Previous studies proposed that ovariole number correlated with oviposition substrate [2, 3, 4] but sampled largely one clade of these flies and were limited by a provisional phylogeny and the available comparative methods. We test this hypothesis by applying phylogenetic modeling to an expanded sampling of ovariole numbers and substrate types and show support for these predictions across all major groups of Hawaiian Drosophila, wherein ovariole number variation is best explained by adaptation to specific substrates. Furthermore, we show that oviposition substrate evolution is linked to changes in the allometric relationship between body size and ovariole number. Finally, we provide evidence that the major changes in ovarian cell number that regulate D. melanogaster ovariole number also regulate ovariole number in Hawaiian drosophilids. Thus, we provide evidence that this remarkable adaptive radiation is linked to evolutionary changes in a key reproductive trait regulated at least partly by variation in the same developmental parameters that operate in the model species D. melanogaster.
  • A Plastic Visual Pathway Regulates Cooperative Behavior in Drosophila
    • Abstract: Publication date: Available online 23 May 2019Source: Current BiologyAuthor(s): Mark Dombrovski, Anna Kim, Leanne Poussard, Andrea Vaccari, Scott Acton, Emma Spillman, Barry Condron, Quan YuanSummaryCooperative behavior emerges in biological systems through coordinated actions among individuals [1, 2]. Although widely observed across animal species, the cellular and molecular mechanisms underlying the establishment and maintenance of cooperative behaviors remain largely unknown [3]. To characterize the circuit mechanisms serving the needs of independent individuals and social groups, we investigated cooperative digging behavior in Drosophila larvae [4, 5, 6]. Although chemical and mechanical sensations are important for larval aggregation at specific sites [7, 8, 9], an individual larva’s ability to participate in a cooperative burrowing cluster relies on direct visual input as well as visual and social experience during development. In addition, vision modulates cluster dynamics by promoting coordinated movements between pairs of larvae [5]. To determine the specific pathways within the larval visual circuit underlying cooperative social clustering, we examined larval photoreceptors (PRs) and the downstream local interneurons (lOLPs) using anatomical and functional studies [10, 11]. Our results indicate that rhodopsin-6-expressing-PRs (Rh6-PRs) and lOLPs are required for both cooperative clustering and movement detection. Remarkably, visual deprivation and social isolation strongly impact the structural and functional connectivity between Rh6-PRs and lOLPs, while at the same time having no effect on the adjacent rhodopsin-5-expressing PRs (Rh5-PRs). Together, our findings demonstrate that a specific larval visual pathway involved in social interactions undergoes experience-dependent modifications during development, suggesting that plasticity in sensory circuits could act as the cellular substrate for social learning, a possible mechanism allowing an animal to integrate into a malleable social environment and engage in complex social behaviors.Graphical Graphical abstract for this article
  • Food for Sex in Bats Revealed as Producer Males Reproduce with Scrounging
    • Abstract: Publication date: Available online 23 May 2019Source: Current BiologyAuthor(s): Lee Harten, Yosef Prat, Shachar Ben Cohen, Roi Dor, Yossi YovelSummaryFood sharing is often evolutionarily puzzling, because the provider’s benefits are not always clear. Sharing among kin may increase indirect fitness [1], but when non-kin are involved, different mechanisms were suggested to act. Occasionally, “tolerated theft” [2, 3] is observed, merely because defending a resource is not cost effective. Sharing may also be explained as “costly signaling” [4, 5], where individuals signal their high qualities by distributing acquired resources, as has been suggested to occur in certain human cultures [6]. Alternatively, a transferred food item might be compensated for in later interactions [7]. In vampire bats, blood sharing reflects reciprocity between non-kin colony members [8, 9, 10], and long-term social bonds affect food sharing in chimpanzees [11]. Food may also be exchanged for other goods or social benefits [12, 13, 14]. One reciprocity-based explanation for intersexual food sharing is the food-for-sex hypothesis [15, 16, 17]. This hypothesis proposes that males share food with females in exchange for mating opportunities. Studies on human hunter-gatherer societies suggest that males with increased foraging success have higher reproductive success [18, 19]. Male chimpanzees, which in contrast to humans do not maintain pair bonds, were suggested to share food with females to increase their mating opportunities [16] (but see [20]). Bats, which are long-lived social mammals [21, 22], provide an opportunity to study long-term social reciprocity mechanisms. We monitored producer-scrounger interactions of a captive Egyptian fruit bat (Rousettus aegyptiacus) colony for more than a year and genetically determined the paternity of the pups that were born in the colony. We found that females carry the young of males from which they used to scrounge food, supporting the food-for-sex hypothesis in this species.
  • Growth at Cold Temperature Increases the Number of Motor Neurons to
           Optimize Locomotor Function
    • Abstract: Publication date: Available online 23 May 2019Source: Current BiologyAuthor(s): Kira A. Spencer, Yesser Hadj Belgacem, Olesya Visina, Sangwoo Shim, Henry Genus, Laura N. BorodinskySummaryDuring vertebrate development, spinal neurons differentiate and connect to generate a system that performs sensorimotor functions critical for survival. Spontaneous Ca2+ activity regulates different aspects of spinal neuron differentiation. It is unclear whether environmental factors can modulate this Ca2+ activity in developing spinal neurons to alter their specialization and ultimately adjust sensorimotor behavior to fit the environment. Here, we show that growing Xenopus laevis embryos at cold temperatures results in an increase in the number of spinal motor neurons in larvae. This change in spinal cord development optimizes the escape response to gentle touch of animals raised in and tested at cold temperatures. The cold-sensitive channel TRPM8 increases Ca2+ spike frequency of developing ventral spinal neurons, which in turn regulates expression of the motor neuron master transcription factor HB9. TRPM8 is necessary for the increase in motor neuron number of animals raised in cold temperatures and for their enhanced sensorimotor behavior when tested at cold temperatures. These findings suggest the environment modulates neuronal differentiation to optimize the behavior of the developing organism.Graphical Graphical abstract for this article
  • Mapping the Whole-Body Muscle Activity of Hydra vulgaris
    • Abstract: Publication date: Available online 23 May 2019Source: Current BiologyAuthor(s): John R. Szymanski, Rafael YusteSummaryHydra is a cnidarian polyp with an anatomically simple neuromuscular system that can offer evolutionary insights on the functional design of animal body plans. Using calcium imaging to map the activity of the entire epitheliomuscular system of behaving Hydra, we find seven basic spatiotemporal patterns of muscle activity. Patterns include global and local activation events with widely varying kinetics of initiation and wave-like propagation. The orthogonally oriented endodermal and ectodermal muscle fibers are jointly activated during longitudinal contractions. Individual epitheliomuscular cells can participate in multiple patterns, even with very different kinetics. This cellular multifunctionality could enable the structurally simple epitheliomuscular tissue of basal metazoans to implement a diverse behavioral output.Graphical Graphical abstract for this article
  • A SNP in a Steroidogenic Enzyme Is Associated with Phenotypic Sex in
           Seriola Fishes
    • Abstract: Publication date: Available online 23 May 2019Source: Current BiologyAuthor(s): Takashi Koyama, Masatoshi Nakamoto, Kagayaki Morishima, Ryohei Yamashita, Takefumi Yamashita, Kohei Sasaki, Yosuke Kuruma, Naoki Mizuno, Moe Suzuki, Yoshiharu Okada, Risa Ieda, Tsubasa Uchino, Satoshi Tasumi, Sho Hosoya, Seiichi Uno, Jiro Koyama, Atsushi Toyoda, Kiyoshi Kikuchi, Takashi SakamotoSummaryVertebrate sex development consists largely of two processes: “sex determination,” the initial bifurcation of sexual identity, and “sex differentiation,” which subsequently facilitates maleness or femaleness according to the sex determination signal. Steroid hormones promote multiple types of sexual dimorphism in eutherian mammals and avians [1, 2, 3], in which they are indispensable for proper sex differentiation. By contrast, in many poikilothermic vertebrates, steroid hormones have been proposed to be key players in sex determination as well as sex differentiation [4, 5, 6, 7, 8]. This hypothesis was introduced more than 50 years ago but has never been rigorously tested due to difficulties in discriminating the roles of steroids in sex determination and differentiation. We found that a missense SNP in the gene encoding the steroidogenic enzyme 17β-hydroxysteroid dehydrogenase 1 (Hsd17b1) was perfectly associated with ZZ/ZW sex determination in Seriola fishes. Biochemical analyses revealed that a glutamate residue present specifically in Z-type HSD17B1 attenuated interconversion between 17-keto and 17β-hydroxy steroids relative to the allelic product from the W chromosome, which harbors glycine at that position, by disrupting the hydrogen bond network between the steroid and the enzyme’s catalytic residues. Hsd17b1 mRNA is constitutively expressed in undifferentiated and differentiating gonads of both genotypic sexes, whereas W-type mRNA is expressed only in genotypic females. Meanwhile, Cyp19a1 is predominantly expressed in differentiating ovary. We conclude that the combination of Hsd17b1 alleles determines sex by modulating endogenous estrogen levels in Seriola species. These findings strongly support the long-standing hypothesis on steroids in sex determination.
  • Simple Acoustic Features Can Explain Phoneme-Based Predictions of Cortical
           Responses to Speech
    • Abstract: Publication date: Available online 23 May 2019Source: Current BiologyAuthor(s): Christoph Daube, Robin A.A. Ince, Joachim GrossSummaryWhen we listen to speech, we have to make sense of a waveform of sound pressure. Hierarchical models of speech perception assume that, to extract semantic meaning, the signal is transformed into unknown, intermediate neuronal representations. Traditionally, studies of such intermediate representations are guided by linguistically defined concepts, such as phonemes. Here, we argue that in order to arrive at an unbiased understanding of the neuronal responses to speech, we should focus instead on representations obtained directly from the stimulus. We illustrate our view with a data-driven, information theoretic analysis of a dataset of 24 young, healthy humans who listened to a 1 h narrative while their magnetoencephalogram (MEG) was recorded. We find that two recent results, the improved performance of an encoding model in which annotated linguistic and acoustic features were combined and the decoding of phoneme subgroups from phoneme-locked responses, can be explained by an encoding model that is based entirely on acoustic features. These acoustic features capitalize on acoustic edges and outperform Gabor-filtered spectrograms, which can explicitly describe the spectrotemporal characteristics of individual phonemes. By replicating our results in publicly available electroencephalography (EEG) data, we conclude that models of brain responses based on linguistic features can serve as excellent benchmarks. However, we believe that in order to further our understanding of human cortical responses to speech, we should also explore low-level and parsimonious explanations for apparent high-level phenomena.
  • Field Experiments and Meta-analysis Reveal Wetland Vegetation as a Crucial
           Element in the Coastal Protection Paradigm
    • Abstract: Publication date: Available online 23 May 2019Source: Current BiologyAuthor(s): Brian R. Silliman, Qiang He, Christine Angelini, Carter S. Smith, Matthew L. Kirwan, Pedro Daleo, Julianna J. Renzi, Jack Butler, Todd Z. Osborne, James C. Nifong, Johan van de KoppelSummaryIncreasing rates of sea-level rise and wave action threaten coastal populations. Defense of shorelines by protection and restoration of wetlands has been invoked as a win-win strategy for humans and nature, yet evidence from field experiments supporting the wetland protection function is uncommon, as is the understanding of its context dependency. Here we provide evidence from field manipulations showing that the loss of wetland vegetation, regardless of disturbance size, increases the rate of erosion on wave-stressed shorelines. Vegetation removal (simulated disturbance) along the edge of salt marshes reveals that loss of wetland plants elevates the rate of lateral erosion and that extensive root systems, rather than aboveground biomass, are primarily responsible for protection against edge erosion in marshes. Meta-analysis further shows that disturbances that generate plant die-off on salt marsh edges generally hasten edge erosion in coastal marshes and that the erosion protection function of wetlands relates more to lateral than vertical edge-erosional processes and is positively correlated with the amount of belowground plant biomass lost. Collectively, our findings substantiate a coastal protection paradigm that incorporates preservation of shoreline vegetation, illuminate key context dependencies in this theory, and highlight local disturbances (e.g., oil spills) that kill wetland plants as agents that can accelerate coastal erosion.
  • Artificially Enhancing and Suppressing Hippocampus-Mediated Memories
    • Abstract: Publication date: Available online 23 May 2019Source: Current BiologyAuthor(s): Briana K. Chen, Nathen J. Murawski, Christine Cincotta, Olivia McKissick, Abby Finkelstein, Anahita B. Hamidi, Emily Merfeld, Emily Doucette, Stephanie L. Grella, Monika Shpokayte, Yosif Zaki, Amanda Fortin, Steve RamirezSummaryEmerging evidence indicates that distinct hippocampal domains differentially drive cognition and emotion [1, 2]; dorsal regions encode spatial, temporal, and contextual information [3, 4, 5], whereas ventral regions regulate stress responses [6], anxiety-related behaviors [7, 8], and emotional states [8, 9, 10]. Although previous studies demonstrate that optically manipulating cells in the dorsal hippocampus can drive the behavioral expression of positive and negative memories, it is unknown whether changes in cellular activity in the ventral hippocampus can drive such behaviors [11, 12, 13, 14]. Investigating the extent to which distinct hippocampal memories across the longitudinal axis modulate behavior could aid in the understanding of stress-related psychiatric disorders known to affect emotion, memory, and cognition [15]. Here, we asked whether tagging and stimulating cells along the dorsoventral axis of the hippocampus could acutely, chronically, and differentially promote context-specific behaviors. Acute reactivation of both dorsal and ventral hippocampus cells that were previously active during memory formation drove freezing behavior, place avoidance, and place preference. Moreover, chronic stimulation of dorsal or ventral hippocampal fear memories produced a context-specific reduction or enhancement of fear responses, respectively, thus demonstrating bi-directional and context-specific modulation of memories along the longitudinal axis of the hippocampus. Fear memory suppression was associated with a reduction in hippocampal cells active during retrieval, while fear memory enhancement was associated with an increase in basolateral amygdala activity. Together, our data demonstrate that discrete sets of cells throughout the hippocampus provide key nodes sufficient to bi-directionally reprogram both the neural and behavioral expression of memory.
  • Plant Biology: Proteolytic Release of Damage Signals
    • Abstract: Publication date: 20 May 2019Source: Current Biology, Volume 29, Issue 10Author(s): Kyoko Morimoto, Renier A.L. van der HoornPlants protect their wounds against pathogen invasion by releasing damage signals that induce immune responses in neighboring cells. A new study shows that a conserved bioactive peptide is released from its cytoplasmic precursor upon wounding by a metacaspase that is activated by calcium influx into the injured cell.
  • Domestication of Industrial Microbes
    • Abstract: Publication date: 20 May 2019Source: Current Biology, Volume 29, Issue 10Author(s): Jan Steensels, Brigida Gallone, Karin Voordeckers, Kevin J. VerstrepenDomestication refers to artificial selection and breeding of wild species to obtain cultivated variants that thrive in man-made niches and meet human or industrial requirements. Several genotypic and phenotypic signatures of domestication have been described in crops, livestock and pets. However, domestication is not unique to plants and animals. Microbial diversity has also been shaped by the emergence of novel and highly specific man-made environments, like food and beverage fermentations. This allowed rapid adaptation and diversification of various microbes, such as certain Lactococcus, Lactobacillus, Oenococcus, Saccharomyces and Aspergillus species. During the domestication process, microbes gained the capacity to efficiently consume particular nutrients, cope with a multitude of industry-specific stress factors and produce desirable compounds, often at the cost of a reduction in fitness in their original, natural environments. Moreover, different lineages of the same species adapted to highly diverse niches, resulting in genetically and phenotypically distinct strains. In this Review, we discuss the basic principles of microbial domestication and describe how recent research is uncovering its genetic underpinnings.
  • Organelle Contact Sites: Lipid Droplets Hooked by Metabolically
           Controlled Tethers
    • Abstract: Publication date: 20 May 2019Source: Current Biology, Volume 29, Issue 10Author(s): Maria BohnertLipid droplets are physically linked to other organelles via contact sites for communication, but the underlying molecular machineries are poorly characterized. Recent studies identify metabolically controlled sorting nexin tether proteins as important players at these sites.
  • Neuroscience: The Hidden Diversity of Electrical Synapses
    • Abstract: Publication date: 20 May 2019Source: Current Biology, Volume 29, Issue 10Author(s): Alberto E. PeredaThe complete description of the expression of gap junction proteins in the nervous system of the worm reveals a great complexity of their distribution amongst different neuronal classes, opening an unprecedented opportunity to expose the functional diversity of electrical synapses.
  • Social Behaviour: Males Help When Mates Are Rare
    • Abstract: Publication date: 20 May 2019Source: Current Biology, Volume 29, Issue 10Author(s): Sjouke A. Kingma, Tamás SzékelyIn cooperatively-breeding animals, some individuals may postpone or completely forego independent reproduction to help others reproduce. A recent large-scale manipulation of adult sex ratio in wild nuthatches suggests that male birds postpone breeding because of a shortage of potential mates.
  • Actin: Post-translational Modification of Actin Linked to Formin
    • Abstract: Publication date: 20 May 2019Source: Current Biology, Volume 29, Issue 10Author(s): Roberto DominguezActin undergoes several forms of post-translational modifications that play roles in normal physiological processes and pathological states. A new study reveals that a complex between lysine-acetylated actin and cyclase-associated protein inhibits the formin INF2 by enhancing intramolecular inhibitory interactions in this protein.
  • Learning and Memory: Mind over Matter in C. elegans
    • Abstract: Publication date: 20 May 2019Source: Current Biology, Volume 29, Issue 10Author(s): Menachem Katz, Shai ShahamThe capacity to respond to adverse conditions is key for animal survival. Research in the nematode Caenorhabditis elegans demonstrates that retrieval of aversive memories, stored within sensory neurons, is sufficient to induce a protective systemic stress response that improves fitness.
  • Evolution: Genomic Signatures of Mimicry and Mimicry of Genomic Signatures
    • Abstract: Publication date: 20 May 2019Source: Current Biology, Volume 29, Issue 10Author(s): Michael Matschiner, Walter SalzburgerHow new species form in the ocean, and thus what determines the diversity of fish in the sea, is not well understood. A study in Caribbean coral-reef fishes sheds light on the genomic underpinnings of diversification in the marine realm.
  • Environmental Stress: Salinity Ruins a Plant’s Day in the Sun
    • Abstract: Publication date: 20 May 2019Source: Current Biology, Volume 29, Issue 10Author(s): Katie J. Magallon, José R. DinnenyNew research reveals how low levels of salinity in soil inhibit a plant’s ability to respond to shade through a signaling mechanism involving the plant stress hormone abscisic acid.
  • Visual Neuroscience: Locomotion Changes How Mice See
    • Abstract: Publication date: 20 May 2019Source: Current Biology, Volume 29, Issue 10Author(s): Richard J. KrauzlisHow sensory signals are processed by the visual cortex is not fixed but changes depending on our spatial goals and whether or not we are moving. New research helps explain why these two effects do not always work well together.
  • Cradles of diversity are unlikely relics of regional climate stability
    • Abstract: Publication date: 20 May 2019Source: Current Biology, Volume 29, Issue 10Author(s): Damien A. Fordham, Stuart C. Brown, Tom M.L. Wigley, Carsten RahbekSummaryThe stability of regional climates on millennial timescales is theorised to be a primary determinant of nearby diversification 1, 2, 3, 4, 5. Using simulated patterns of past temperature change at monthly timescales [6], we show that the locations of climatically stable regions are likely to have varied considerably across and within millennia during glacial–interglacial cycles of the Late Quaternary. This result has important implications for the role of regional climate stability in theories of speciation, because long-term climate refugia are typically presumed to be ‘cradles’ of diversity (areas of high speciation) only if they remain stable across Milankovitch climate oscillations 1, 2, 3, 4, 5, which operate on multi-millennial time scales [7].
  • Males with a mother living in their group have higher paternity success in
           bonobos but not chimpanzees
    • Abstract: Publication date: 20 May 2019Source: Current Biology, Volume 29, Issue 10Author(s): Martin Surbeck, Christophe Boesch, Catherine Crockford, Melissa Emery Thompson, Takeshi Furuichi, Barbara Fruth, Gottfried Hohmann, Shintaro Ishizuka, Zarin Machanda, Martin N. Muller, Anne Pusey, Tetsuya Sakamaki, Nahoko Tokuyama, Kara Walker, Richard Wrangham, Emily Wroblewski, Klaus Zuberbühler, Linda Vigilant, Kevin LangergraberSummaryIn many group-living mammals, mothers may increase the reproductive success of their daughters even after they are nutritionally independent and fully grown [1]. However, whether such maternal effects exist for adult sons is largely unknown. Here we show that males have higher paternity success when their mother is living in the group at the time of the offspring’s conception in bonobos (N = 39 paternities from 4 groups) but not in chimpanzees (N = 263 paternities from 7 groups). These results are consistent with previous research showing a stronger role of mothers (and females more generally) in bonobo than chimpanzee societies.
  • Elephantfish
    • Abstract: Publication date: 20 May 2019Source: Current Biology, Volume 29, Issue 10Author(s): Justin R. Rizzari, Brittany Finucci
  • David Reznick
    • Abstract: Publication date: 20 May 2019Source: Current Biology, Volume 29, Issue 10Author(s): David Reznick
  • Tricks of the mind
    • Abstract: Publication date: 20 May 2019Source: Current Biology, Volume 29, Issue 10Author(s): Nicola S. Clayton, Clive A.P. Wilkins
  • How birds evolved to be different
    • Abstract: Publication date: 20 May 2019Source: Current Biology, Volume 29, Issue 10Author(s): Michael GrossSummaryBirds share a number of unique features setting them apart from other vertebrates. These range from their anatomical adaptations to reproductive traits and behaviour. New fossil discoveries and advances in genomics and have shed light on the evolution of these remarkable differences. Michael Gross reports.
  • Nucleus Isthmi Is Required to Sustain Target Pursuit during Visually
           Guided Prey-Catching
    • Abstract: Publication date: Available online 16 May 2019Source: Current BiologyAuthor(s): Pedro M. Henriques, Niloy Rahman, Samuel E. Jackson, Isaac H. BiancoSummaryAnimals must frequently perform a sequence of behaviors to achieve a specific goal. However, the neural mechanisms that promote the continuation and completion of such action sequences are not well understood. Here, we characterize the anatomy, physiology, and function of the nucleus isthmi (NI), a cholinergic nucleus thought to modulate tectal-dependent, goal-directed behaviors. We find that the larval zebrafish NI establishes reciprocal connectivity with the optic tectum and identify two distinct types of isthmic projection neuron that either connect ipsilaterally to retinorecipient laminae of the tectum and pretectum or bilaterally to both tectal hemispheres. Laser ablation of NI caused highly specific deficits in tectally mediated loom-avoidance and prey-catching behavior. In the context of hunting, NI ablation did not affect prey detection or hunting initiation but resulted in larvae failing to sustain prey-tracking sequences and aborting their hunting routines. Moreover, calcium imaging revealed elevated neural activity in NI following onset of hunting behavior. We propose a model in which NI provides state-dependent feedback facilitation to the optic tectum and pretectum to potentiate neural activity and increase the probability of consecutive prey-tracking maneuvers during hunting sequences.Graphical Graphical abstract for this article
  • Mitigating Anticipated Effects of Systematic Errors Supports Sister-Group
           Relationship between Xenacoelomorpha and Ambulacraria
    • Abstract: Publication date: Available online 16 May 2019Source: Current BiologyAuthor(s): Hervé Philippe, Albert J. Poustka, Marta Chiodin, Katharina J. Hoff, Christophe Dessimoz, Bartlomiej Tomiczek, Philipp H. Schiffer, Steven Müller, Daryl Domman, Matthias Horn, Heiner Kuhl, Bernd Timmermann, Noriyuki Satoh, Tomoe Hikosaka-Katayama, Hiroaki Nakano, Matthew L. Rowe, Maurice R. Elphick, Morgane Thomas-Chollier, Thomas Hankeln, Florian MertesSummaryXenoturbella and the acoelomorph worms (Xenacoelomorpha) are simple marine animals with controversial affinities. They have been placed as the sister group of all other bilaterian animals (Nephrozoa hypothesis), implying their simplicity is an ancient characteristic [1, 2]; alternatively, they have been linked to the complex Ambulacraria (echinoderms and hemichordates) in a clade called the Xenambulacraria [3, 4, 5], suggesting their simplicity evolved by reduction from a complex ancestor. The difficulty resolving this problem implies the phylogenetic signal supporting the correct solution is weak and affected by inadequate modeling, creating a misleading non-phylogenetic signal. The idea that the Nephrozoa hypothesis might be an artifact is prompted by the faster molecular evolutionary rate observed within the Acoelomorpha. Unequal rates of evolution are known to result in the systematic artifact of long branch attraction, which would be predicted to result in an attraction between long-branch acoelomorphs and the outgroup, pulling them toward the root [6]. Other biases inadequately accommodated by the models used can also have strong effects, exacerbated in the context of short internal branches and long terminal branches [7]. We have assembled a large and informative dataset to address this problem. Analyses designed to reduce or to emphasize misleading signals show the Nephrozoa hypothesis is supported under conditions expected to exacerbate errors, and the Xenambulacraria hypothesis is preferred in conditions designed to reduce errors. Our reanalyses of two other recently published datasets [1, 2] produce the same result. We conclude that the Xenacoelomorpha are simplified relatives of the Ambulacraria.
  • Pheromones and Nutritional Signals Regulate the Developmental Reliance on
           let-7 Family MicroRNAs in C.¬†elegans
    • Abstract: Publication date: Available online 16 May 2019Source: Current BiologyAuthor(s): Orkan Ilbay, Victor AmbrosSummaryAdverse environmental conditions can affect rates of animal developmental progression and lead to temporary developmental quiescence (diapause), exemplified by the dauer larva stage of the nematode Caenorhabditis elegans (C. elegans). Remarkably, patterns of cell division and temporal cell-fate progression in C. elegans larvae are not affected by changes in developmental trajectory. However, the underlying physiological and gene regulatory mechanisms that ensure robust developmental patterning despite substantial plasticity in developmental progression are largely unknown. Here, we report that diapause-inducing pheromones correct heterochronic developmental cell lineage defects caused by insufficient expression of let-7 family microRNAs in C. elegans. Moreover, two conserved endocrine signaling pathways, DAF-7/TGF-β and DAF-2/Insulin, that confer on the larva diapause and non-diapause alternative developmental trajectories interact with the nuclear hormone receptor, DAF-12, to initiate and regulate a rewiring of the genetic circuitry controlling temporal cell fates. This rewiring includes engagement of certain heterochronic genes, lin-46, lin-4, and nhl-2, that are previously associated with an altered genetic program in post-diapause animals, in combination with a novel ligand-independent DAF-12 activity, to downregulate the critical let-7 family target Hunchback-like-1 (HBL-1). Our results show how pheromone or endocrine signaling pathways can coordinately regulate both developmental progression and cell-fate transitions in C. elegans larvae under stress so that the developmental schedule of cell fates remains unaffected by changes in developmental trajectory.Graphical Graphical abstract for this article
  • Distinct RopGEFs Successively Drive Polarization and Outgrowth of Root
    • Abstract: Publication date: Available online 16 May 2019Source: Current BiologyAuthor(s): Philipp Denninger, Anna Reichelt, Vanessa A.F. Schmidt, Dietmar G. Mehlhorn, Lisa Y. Asseck, Claire E. Stanley, Nana F. Keinath, Jan-Felix Evers, Christopher Grefen, Guido GrossmannSummaryRoot hairs are tubular protrusions of the root epidermis that significantly enlarge the exploitable soil volume in the rhizosphere. Trichoblasts, the cell type responsible for root hair formation, switch from cell elongation to tip growth through polarization of the growth machinery to a predefined root hair initiation domain (RHID) at the plasma membrane. The emergence of this polar domain resembles the establishment of cell polarity in other eukaryotic systems [1, 2, 3]. Rho-type GTPases of plants (ROPs) are among the first molecular determinants of the RHID [4, 5], and later play a central role in polar growth [6]. Numerous studies have elucidated mechanisms that position the RHID in the cell [7, 8, 9] or regulate ROP activity [10, 11, 12, 13, 14, 15, 16, 17, 18]. The molecular players that target ROPs to the RHID and initiate outgrowth, however, have not been identified. We dissected the timing of the growth machinery assembly in polarizing hair cells and found that positioning of molecular players and outgrowth are temporally separate processes that are each controlled by specific ROP guanine nucleotide exchange factors (GEFs). A functional analysis of trichoblast-specific GEFs revealed GEF3 to be required for normal ROP polarization and thus efficient root hair emergence, whereas GEF4 predominantly regulates subsequent tip growth. Ectopic expression of GEF3 induced the formation of spatially confined, ROP-recruiting domains in other cell types, demonstrating the role of GEF3 to serve as a membrane landmark during cell polarization.Graphical Graphical abstract for this article
  • The Spatial Resolution of Bat Biosonar Quantified with a Visual-Resolution
    • Abstract: Publication date: Available online 16 May 2019Source: Current BiologyAuthor(s): Cornelia Geberl, Kathrin Kugler, Lutz WiegrebeSummaryBats are navigation super-performers, flying at high speed through nocturnal forests. Numerous field observations and formal experiments have impressively shown how well bats tackle navigation in 3D with biosonar, i.e., the auditory analysis of self-generated ultrasonic emissions [1, 2, 3, 4, 5, 6, 7]. However, unlike in the visual system, where space is explicitly coded at very high resolution in the retinal fovea, the inner ear encodes frequency and time, not space. Spatial attributes of echoes are represented in the space-dependent filtering of the bats’ pinnae [8, 9] and binaural computations, like interaural time and level differences [10, 11], as first proposed by Lord Rayleigh [12]. Remarkably, Rayleigh also provided a clear definition of spatial resolution: based on the shape of optical diffraction patterns arising from two closely spaced light sources, Rayleigh defined resolution as the capability to detect a trough in their joint light diffraction patterns [13, 14]. Here, we recruit Rayleigh’s classical resolution paradigm to quantify how well bats can resolve multiple simultaneously presented reflectors in space. We show that biosonar spatial resolution in azimuth is no better than about 80° compared to a human visual resolution down to 0.02° [14]. We suggest that bats compensate this effective lack of spatial resolution by sequentially probing their environment in flight. Our data show that low-resolution environment perception is a viable alternative to high-resolution vision to support intelligent behavior in complex environments.
  • Mechanistic Origin of Cell-Size Control and Homeostasis in Bacteria
    • Abstract: Publication date: Available online 16 May 2019Source: Current BiologyAuthor(s): Fangwei Si, Guillaume Le Treut, John T. Sauls, Stephen Vadia, Petra Anne Levin, Suckjoon JunSummaryEvolutionarily divergent bacteria share a common phenomenological strategy for cell-size homeostasis under steady-state conditions. In the presence of inherent physiological stochasticity, cells following this “adder” principle gradually return to their steady-state size by adding a constant volume between birth and division, regardless of their size at birth. However, the mechanism of the adder has been unknown despite intense efforts. In this work, we show that the adder is a direct consequence of two general processes in biology: (1) threshold—accumulation of initiators and precursors required for cell division to a respective fixed number—and (2) balanced biosynthesis—maintenance of their production proportional to volume growth. This mechanism is naturally robust to static growth inhibition but also allows us to “reprogram” cell-size homeostasis in a quantitatively predictive manner in both Gram-negative Escherichia coli and Gram-positive Bacillus subtilis. By generating dynamic oscillations in the concentration of the division protein FtsZ, we were able to oscillate cell size at division and systematically break the adder. In contrast, periodic induction of replication initiator protein DnaA caused oscillations in cell size at initiation but did not alter division size or the adder. Finally, we were able to restore the adder phenotype in slow-growing E. coli, the only known steady-state growth condition wherein E. coli significantly deviates from the adder, by repressing active degradation of division proteins. Together, these results show that cell division and replication initiation are independently controlled at the gene-expression level and that division processes exclusively drive cell-size homeostasis in bacteria.Graphical Graphical abstract for this article
  • Neuronal Substrates for Infrared Contrast Enhancement and Motion Detection
           in Rattlesnakes
    • Abstract: Publication date: Available online 16 May 2019Source: Current BiologyAuthor(s): Maximilian S. Bothe, Harald Luksch, Hans Straka, Tobias KohlSummaryPit vipers detect infrared (IR) radiation with loreal pit organs [1] that are connected to the hindbrain by trigeminal nerve fibers [2, 3, 4]. The pattern of central afferent termination forms a topographical representation of the sensory periphery within the nucleus of the lateral descending trigeminal tract (LTTD) [4, 5, 6, 7]. All LTTD neurons project to another specialized, ipsilateral hindbrain area, the nucleus reticularis caloris (RC) [8, 9, 10, 11], before IR signals are integrated with visual signals in the optic tectum [12, 13]. Pit-organ-innervating afferent fibers provoke in individual LTTD neurons a direct, robust spike activity upon peripheral activation [7, 14]. This discharge is truncated by an indirect, delayed synaptic inhibition from afferent fibers of adjacent sensory areas through parallel microcircuitry that converges with afferent fibers onto the same target neurons [7]. Here, we determined the impact of this interaction on IR contrast enhancement and/or motion detection in LTTD and RC neurons using isolated whole-brain preparations of rattlesnakes with intact pit organs. Simulated and real IR source motion provoked weak directional tuning of the discharge in LTTD neurons and RC neurons expressed a strong, motion-direction-differentiating activity. The hierarchically increasing motion sensitivity potentially derives from a direction-specific inhibition or spike frequency adaptation of LTTD neuronal discharge that becomes further pronounced by convergent projections onto individual RC neurons. The emerging signaling pattern complies with contrast enhancement (LTTD) and extraction of movement-related signals (RC), thereby forming a motion detection mechanism that encodes moving IR sources relative to the ambient temperature [14].Graphical Graphical abstract for this article
  • Bedbugs Evolved before Their Bat Hosts and Did Not Co-speciate with
           Ancient Humans
    • Abstract: Publication date: Available online 16 May 2019Source: Current BiologyAuthor(s): Steffen Roth, Ondřej Balvín, Michael T. Siva-Jothy, Osvaldo Di Iorio, Petr Benda, Omar Calva, Eduardo I. Faundez, Faisal Ali Anwarali Khan, Mary McFadzen, Margie P. Lehnert, Richard Naylor, Nikolay Simov, Edward H. Morrow, Endre Willassen, Klaus ReinhardtSummaryAll 100+ bedbug species (Cimicidae) are obligate blood-sucking parasites [1, 2]. In general, blood sucking (hematophagy) is thought to have evolved in generalist feeders adventitiously taking blood meals [3, 4], but those cimicid taxa currently considered ancestral are putative host specialists [1, 5]. Bats are believed to be the ancestral hosts of cimicids [1], but a cimicid fossil [6] predates the oldest known bat fossil [7] by>30 million years (Ma). The bedbugs that parasitize humans [1, 8] are host generalists, so their evolution from specialist ancestors is incompatible with the “resource efficiency” hypothesis and only partially consistent with the “oscillation” hypothesis [9, 10, 11, 12, 13, 14, 15, 16]. Because quantifying host shift frequencies of hematophagous specialists and generalists may help to predict host associations when vertebrate ranges expand by climate change [17], livestock, and pet trade in general and because of the previously proposed role of human pre-history in parasite speciation [18, 19, 20], we constructed a fossil-dated, molecular phylogeny of the Cimicidae. This phylogeny places ancestral Cimicidae to 115 mya as hematophagous specialists with lineages that later frequently populated bat and bird lineages. We also found that the clades, including the two major current urban pests, Cimex lectularius and C. hemipterus, separated 47 mya, rejecting the notion that the evolutionary trajectories of Homo caused their divergence [18, 19, 20, 21].
  • Multiple Auxin-Response Regulators Enable Stability and Variability in
           Leaf Development
    • Abstract: Publication date: Available online 16 May 2019Source: Current BiologyAuthor(s): Alon Israeli, Yossi Capua, Ido Shwartz, Lior Tal, Zohar Meir, Matan Levy, Maya Bar, Idan Efroni, Naomi OriSummaryAuxin-signal transduction is mediated by the antagonistic activity of transcriptional activators and repressors. Both activators and repressors belong to gene families, but the biological importance of this complexity is not clear. Here, we addressed this question using tomato leaf development as a model by generating and analyzing mutants in multiple auxin-response components. In developing compound tomato leaves, auxin promotes leaflet formation and blade growth, and in the intercalary regions between leaflets, auxin response is inhibited by the Aux/IAA protein ENTIRE (E). e mutants form simple leaves due to ectopic blade growth in the intercalary domain. Using this unique loss-of-function phenotype and genome editing of auxin-response factor (ARF) genes, encoding auxin-response activators, we identified the contribution of specific ARFs to the e phenotype. Mutations in the related ARFs SlMP, SlARF19A, and SlARF19B, but not SlARF7, reduced the leaf blade and suppressed the e phenotype in a dosage-dependent manner that correlated with their relative expression, leading to a continuum of shapes. While single e and slmp mutants affected blade growth in an opposite manner, leaves of e slmp double mutants were similar to those of the wild type. However, the leaf shape of e slmp was more variable than that of the wild type, and it showed increased sensitivity to auxin. Our findings demonstrate that the existence of multiple auxin-response repressors and activators stabilizes the developmental output of auxin and that tuning their activity enables shape variability. The increased complexity of the auxin response therefore balances stability and flexibility in leaf patterning.Graphical Graphical abstract for this article
  • Drosophila Acquires a Long-Lasting Body-Size Memory from Visual
    • Abstract: Publication date: Available online 16 May 2019Source: Current BiologyAuthor(s): Tammo Krause, Laura Spindler, Burkhard Poeck, Roland StraussSummaryGrasping an object or crossing a trench requires the integration of information on the operating distance of our limbs with precise distance estimation. The reach of our hands and step size of our legs are learned by the visual feedback we get during our actions. This implicit knowledge of our peripersonal space is first acquired during infancy but will be continuously updated throughout our whole life [1]. In contrast, body size of holometabolous insects does not change after metamorphosis; nevertheless, they do have to learn their body reaches at least once. The body size of Drosophila imagines can vary by about 15% depending on environmental factors like food quality and temperature [2]. To investigate how flies acquire knowledge about and memorize their body size, we studied their decisions to either refrain from or initiate climbing over gaps exceeding their body size [3]. Naive (dark-reared) flies overestimate their size and have to learn it from the parallax motion of the retinal images of objects in their environment while walking. Naive flies can be trained in a striped arena and manipulated to underestimate their size, but once consolidated, this memory seems to last for a lifetime. Consolidation of this memory is stress sensitive only in the first 2 h after training but cannot be retrieved for the next 12 h. We have identified a set of intrinsic, lateral neurons of the protocerebral bridge of the central complex [4, 5] that depend on dCREB2 transcriptional activity for long-term memory consolidation and maintenance.Graphical Graphical abstract for this article
  • Three Genes Define a Bacterial-Like Arsenic Tolerance Mechanism in the
           Arsenic Hyperaccumulating Fern Pteris vittata
    • Abstract: Publication date: Available online 9 May 2019Source: Current BiologyAuthor(s): Chao Cai, Nadia A. Lanman, Kelley A. Withers, Alyssa M. DeLeon, Qiong Wu, Michael Gribskov, David E. Salt, Jo Ann BanksSummaryArsenic is a carcinogenic contaminant of water and food and a growing threat to human health in many regions of the world. This study focuses on the fern Pteris vittata (Pteridaceae), which is extraordinary in its ability to tolerate and hyperaccumulate very high levels of arsenic that would kill any other plant or animal outside the Pteridaceae. Here, we use RNA-seq to identify three genes (GLYCERALDEHYDE 3-PHOSPHATE DEHYDROGENASE (PvGAPC1), ORGANIC CATION TRANSPORTER 4 (PvOCT4), and GLUTATHIONE S-TRANSFERASE (PvGSTF1) that are highly upregulated by arsenic and are necessary for arsenic tolerance, as demonstrated by RNAi. The proteins encoded by these genes have unexpected properties: PvGAPC1 has an unusual active site and a much greater affinity for arsenate than phosphate; PvGSTF1 has arsenate reductase activity; and PvOCT4 localizes as puncta in the cytoplasm. Surprisingly, PvGAPC1, PvGSTF1, and arsenate localize in a similar pattern. These results are consistent with a model that describes the fate of arsenate once it enters the cell. It involves the conversion of arsenate into 1-arseno-3-phosphoglycerate by PvGAPC1. This “chemically trapped” arsenate is pumped into specific arsenic metabolizing vesicles by the PvOCT4 protein. Once inside these vesicles, 1-arseno-3-phosphoglycerate hydrolyses to release arsenate, which is then reduced by PvGSTF1 to arsenite, the form of arsenic stored in the vacuoles of this fern. This mechanism is strikingly similar to one recently described Pseudomonas aeruginosa, whose tolerance to arsenic also involves the biosynthesis and transport of 1-arseno-3-phosphoglycerate, indicating that P. vittata has evolved a simple, bacterial-like mechanism for arsenic tolerance.
  • Post-transcriptional Regulation of FLOWERING LOCUS T Modulates
           Heat-Dependent Source-Sink Development in Potato
    • Abstract: Publication date: Available online 2 May 2019Source: Current BiologyAuthor(s): Günter G. Lehretz, Sophia Sonnewald, Csaba Hornyik, José M. Corral, Uwe SonnewaldSummaryUnderstanding tuberization in the major crop plant potato (Solanum tuberosum L.) is of importance to secure yield even under changing environmental conditions. Tuber formation is controlled by a homolog of the floral inductor FLOWERING LOCUS T, referred to as SP6A. To gain deeper insights into its function, we created transgenic potato plants overexpressing a codon-optimized version of SP6A, SP6Acop, to avoid silencing effects. These plants exhibited extremely early tuberization at the juvenile stage, hindering green biomass development and indicating a tremendous shift in the source sink balance. The meristem identity was altered in dormant buds of transgenic tubers. This strong phenotype, not being reported so far for plants overexpressing an unmodified SP6A, could be due to post-transcriptional regulation. In fact, a putative SP6A-specific small regulatory RNA was identified in potato. It was effectively repressing SP6A mRNA accumulation in transient assays as well as in leaves of young potato plants prior to tuber formation. SP6A expression is downregulated under heat, preventing tuberization. The molecular mechanism has not been elucidated yet. We showed that this small RNA is strongly upregulated under heat. The importance of the small RNA was demonstrated by overexpression of a target mimicry construct, which led to an increased SP6A expression, enabling tuberization even under continuous heat conditions, which abolished tuber formation in the wild-type. Thus, our study describes an additional regulatory mechanism for SP6A besides the well-known pathway that integrates both developmental and environmental signals to control tuberization and is therefore a promising target for breeding of heat-tolerant potato.Graphical Graphical abstract for this article
  • A Memory Circuit for Coping with Impending Adversity
    • Abstract: Publication date: Available online 2 May 2019Source: Current BiologyAuthor(s): Yifat Eliezer, Noa Deshe, Lihi Hoch, Shachar Iwanir, Christian O. Pritz, Alon ZaslaverSummaryOrganisms’ capacity to anticipate future conditions is key for survival. Associative memories are instrumental for learning from past experiences, yet little is known about the processes that follow memory retrieval and their potential advantage in preparing for impending developments. Here, using C. elegans nematodes, we demonstrate that odor-evoked retrieval of aversive memories induces rapid and protective stress responses, which increase animal survival prospects when facing imminent adversities. The underlying mechanism relies on two sensory neurons: one is necessary during the learning period, and the other is necessary and sufficient for memory retrieval. Downstream of memory reactivation, serotonin secreted from two head neurons mediates the systemic stress response. Thus, evoking stressful memories, stored within individual sensory neurons, allows animals to anticipate upcoming dire conditions and provides a head start to initiate rapid and protective responses that ultimately increase animal fitness.
  • Neural Signatures of Prediction Errors in a Decision-Making Task Are
           Modulated by Action Execution Failures
    • Abstract: Publication date: Available online 2 May 2019Source: Current BiologyAuthor(s): Samuel D. McDougle, Peter A. Butcher, Darius E. Parvin, Fasial Mushtaq, Yael Niv, Richard B. Ivry, Jordan A. TaylorSummaryDecisions must be implemented through actions, and actions are prone to error. As such, when an expected outcome is not obtained, an individual should be sensitive to not only whether the choice itself was suboptimal but also whether the action required to indicate that choice was executed successfully. The intelligent assignment of credit to action execution versus action selection has clear ecological utility for the learner. To explore this, we used a modified version of a classic reinforcement learning task in which feedback indicated whether negative prediction errors were, or were not, associated with execution errors. Using fMRI, we asked if prediction error computations in the human striatum, a key substrate in reinforcement learning and decision making, are modulated when a failure in action execution results in the negative outcome. Participants were more tolerant of non-rewarded outcomes when these resulted from execution errors versus when execution was successful, but reward was withheld. Consistent with this behavior, a model-driven analysis of neural activity revealed an attenuation of the signal associated with negative reward prediction errors in the striatum following execution failures. These results converge with other lines of evidence suggesting that prediction errors in the mesostriatal dopamine system integrate high-level information during the evaluation of instantaneous reward outcomes.
  • Corvo, Crick and Uncle Syd: For Sydney Brenner, 1927–2019
    • Abstract: Publication date: Available online 2 May 2019Source: Current BiologyAuthor(s): Alexander Gann
  • Local and Global Influences of Visual Spatial Selection and Locomotion in
           Mouse Primary Visual Cortex
    • Abstract: Publication date: Available online 2 May 2019Source: Current BiologyAuthor(s): Ethan G. McBride, Su-Yee J. Lee, Edward M. CallawaySummarySensory selection and movement locally and globally modulate neural responses in seemingly similar ways. For example, locomotion enhances visual responses in mouse primary visual cortex (V1), resembling the effects of spatial attention on primate visual cortical activity. However, interactions between these local and global mechanisms and the resulting effects on perceptual behavior remain largely unknown. Here, we describe a novel mouse visual spatial selection task in which animals either monitor one of two locations for a contrast change (“selective mice”) or monitor both (“non-selective mice”) and can run at will. Selective mice perform well only when their selected stimulus changes, giving rise to local electrophysiological changes in the corresponding hemisphere of V1 including decreased noise correlations and increased visual information. Non-selective mice perform well when either stimulus changes, giving rise to global changes across both hemispheres of V1. During locomotion, selective mice have worse behavioral performance, increased noise correlations in V1, and decreased visual information, while non-selective mice have decreased noise correlations in V1 but no change in performance or visual information. Our findings demonstrate that mice can locally or globally enhance visual information, but the interaction of the global effect of locomotion with local selection impairs behavioral performance. Moving forward, this mouse model will facilitate future studies of local and global sensory modulatory mechanisms and their effects on behavior.
  • Yeast Spontaneous Mutation Rate and Spectrum Vary with Environment
    • Abstract: Publication date: Available online 2 May 2019Source: Current BiologyAuthor(s): Haoxuan Liu, Jianzhi ZhangSummaryMutation is the ultimate genetic source of evolution and biodiversity, but to what extent the environment impacts mutation rate and spectrum is poorly understood. Past studies discovered mutagenesis induced by antibiotic treatment or starvation, but its relevance and importance to long-term evolution is unclear because these severe stressors typically halt cell growth and/or cause substantial cell deaths. Here, we quantify the mutation rate and spectrum in Saccharomyces cerevisiae by whole-genome sequencing following mutation accumulation in each of seven environments with relatively rapid cell growths and minimal cell deaths. We find the point mutation rate per generation to differ by 3.6-fold among the seven environments, generally increasing in environments with slower cell growths. This trend renders the mutation rate per year more constant than that per generation across environments, which has implications for neutral evolution and the molecular clock. Additionally, we find substantial among-environment variations in mutation spectrum, such as the transition to transversion ratio and AT mutational bias. Other main mutation types, including small insertion or deletion, segmental duplication or deletion, and chromosome gain or loss also tend to occur more frequently in environments where yeast grows more slowly. In contrast to these findings from the nuclear genome, the yeast mitochondrial mutation rate rises with the growth rate, consistent with the metabolic rate hypothesis. Together, these observations indicate that environmental changes, which are ubiquitous in nature, influence not only natural selection, but also the amount and type of mutations available to selection, and suggest that ignoring the latter impact, as is currently practiced, may mislead evolutionary inferences.Graphical Graphical abstract for this article
  • Sydney Brenner (1927–2019)
    • Abstract: Publication date: Available online 2 May 2019Source: Current BiologyAuthor(s): Jonathan Hodgkin
School of Mathematical and Computer Sciences
Heriot-Watt University
Edinburgh, EH14 4AS, UK
Tel: +00 44 (0)131 4513762
Fax: +00 44 (0)131 4513327
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