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Current Biology
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ISSN (Print) 0960-9822 - ISSN (Online) 1879-0445
Published by Elsevier Homepage  [3183 journals]
  • Avian Brains: Primate-like Functions of Neurons in the Crow
    • Abstract: Publication date: 19 August 2019Source: Current Biology, Volume 29, Issue 16Author(s): Michael ColomboDespite the negative connotations of the term ‘birdbrain’, birds possess cognitive abilities on par with primates. A new study finds that neurons in the crow’s brain display characteristics similar to those displayed by neurons in the primate’s brain.
  • Memory Performance Influences Male Reproductive Success in a Wild Bird
    • Abstract: Publication date: 19 August 2019Source: Current Biology, Volume 29, Issue 16Author(s): Rachael C. Shaw, Regan D. MacKinlay, Nicola S. Clayton, Kevin C. Burns
  • A Single MicroRNA-Hox Gene Module Controls Equivalent Movements in
           Biomechanically Distinct Forms of Drosophila
    • Abstract: Publication date: 19 August 2019Source: Current Biology, Volume 29, Issue 16Author(s): A. Raouf Issa, João Picao-Osorio, Nuno Rito, M. Eugenia Chiappe, Claudio R. AlonsoSummaryMovement is the main output of the nervous system. It emerges during development to become a highly coordinated physiological process essential to survival and adaptation of the organism to the environment. Similar movements can be observed in morphologically distinct developmental stages of an organism, but it is currently unclear whether or not these movements have a common molecular cellular basis. Here we explore this problem in Drosophila, focusing on the roles played by the microRNA (miRNA) locus miR-iab4/8, which we previously showed to be essential for the normal corrective response displayed by the fruit fly larva when turned upside down (self-righting). Our study shows that miR-iab4 is required for normal self-righting across all three Drosophila larval stages. Unexpectedly, we also discover that this miRNA is essential for normal self-righting behavior in the adult fly, an organism with different morphology, neural constitution, and biomechanics. Through the combination of gene expression, optical imaging, and quantitative behavioral approaches, we provide evidence that miR-iab4 exerts its effects on adult self-righting behavior in part through repression of the Hox gene Ultrabithorax (Ubx) in a specific set of adult motor neurons, the NB2-3/lin15 neurons. Our results show that miRNA controls the function, rather than the morphology, of these neurons and demonstrate that post-developmental changes in Hox gene expression can modulate behavior in the adult. Our work reveals that a common miRNA-Hox genetic module can be re-deployed in different neurons to control functionally equivalent movements in biomechanically distinct organisms and describes a novel post-developmental role of the Hox genes in adult neural function.
  • Progress towards the Tree of Eukaryotes
    • Abstract: Publication date: 19 August 2019Source: Current Biology, Volume 29, Issue 16Author(s): Patrick J. Keeling, Fabien BurkiDeveloping a detailed understanding of how all known forms of life are related to one another in the tree of life has been a major preoccupation of biology since the idea of tree-like evolution first took hold. Since most life is microbial, our intuitive use of morphological comparisons to infer relatedness only goes so far, and molecular sequence data, most recently from genomes and transcriptomes, has been the primary means to infer these relationships. For prokaryotes this presented new challenges, since the degree of horizontal gene transfer led some to question the tree-like depiction of evolution altogether. Most eukaryotes are also microbial, but in contrast to prokaryotic life, the application of large-scale molecular data to the tree of eukaryotes has largely been a constructive process, leading to a small number of very diverse lineages, or ‘supergroups’. The tree is not completely resolved, and contentious problems remain, but many well-established supergroups now encompass much more diversity than the traditional kingdoms. Some of the most exciting recent developments come from the discovery of branches in the tree that we previously had no inkling even existed, many of which are of great ecological or evolutionary interest. These new branches highlight the need for more exploration, by high-throughput molecular surveys, but also more traditional means of observations and cultivation.
  • REM Sleep: What Is It Good For'
    • Abstract: Publication date: 19 August 2019Source: Current Biology, Volume 29, Issue 16Author(s): Katherine E. Miller, Philip R. GehrmanRapid eye movement (REM) sleep serves an important function for processing and consolidating emotional memory. A recent study shows that restless REM sleep impedes this overnight process, providing insights into psychological disorders marked by fragmented REM sleep.
  • Plant Development: How Leaves Take Shape
    • Abstract: Publication date: 19 August 2019Source: Current Biology, Volume 29, Issue 16Author(s): James W. Satterlee, Michael J. ScanlonLive imaging, genetics, and computational modeling reveal how simple versus compound leaves are formed. Cross-species differences in leaf-wide growth determine the outcome of a locally-acting patterning process.
  • Behavioural Ecology: Sleeping Safely Carries Energetic Costs
    • Abstract: Publication date: 19 August 2019Source: Current Biology, Volume 29, Issue 16Author(s): Lauren Tworkowski, John A. LeskuTrade-offs shape animal behaviour. For decades, the study of trade-offs has provided insight into how animals make decisions, but they have rarely been explored in relation to sleep. A new study reveals a role for sleep in saving energy in garden warblers on a stopover during a northward migration, but with ecological costs.
  • Germline Evolution: Sequestered Cells or Immortal Strands'
    • Abstract: Publication date: 19 August 2019Source: Current Biology, Volume 29, Issue 16Author(s): Duur K. AanenMutation accumulation in long-lived fairy-ring mushrooms is orders of magnitude lower than predicted based on per-cell division mutation rates in other organisms. A possible explanation is the maintenance of ‘immortal’ template-DNA in the active periphery of the fairy ring.
  • Conservation: The Costs of Inbreeding and of Being Inbred
    • Abstract: Publication date: 19 August 2019Source: Current Biology, Volume 29, Issue 16Author(s): Lewis G. Spurgin, Matthew J.G. GageEndangered species face a huge array of challenges, including the negative consequences of individuals having to breed with close genetic relatives. But just how costly is inbreeding in small populations' New research from an endangered bird species suggests that considering inbreeding could be crucial for conservation programmes.
  • Palaeobotany: The Rise of the Earth’s Early Forests
    • Abstract: Publication date: 19 August 2019Source: Current Biology, Volume 29, Issue 16Author(s): Christopher M. BerryRare fossil forests are the best evidence for the ecology of the pioneering large land plants that transformed the Earth system and the terrestrial environment. A new study reveals a spectacular, remarkably extensive early fossil forest in China and sheds light on the evolution of key rooting systems.
  • Evolution: How Bat Biosonar Bests Prey Camouflage
    • Abstract: Publication date: 19 August 2019Source: Current Biology, Volume 29, Issue 16Author(s): A. Leonie BaierThe detection of silent, motionless prey sitting directly on leaves has long been considered a task impossible to solve with echolocation alone. Now, a new study has identified a strategy that lets bats do just that — with the help of the leaf.
  • The high speed radular prey strike of a fish-hunting cone snail
    • Abstract: Publication date: 19 August 2019Source: Current Biology, Volume 29, Issue 16Author(s): Joseph R. Schulz, Ian Jan, Gurleen Sangha, Emanuel AziziSummaryCone snails are venomous marine gastropods that hydraulically propel a hollow, chitinous radular harpoon into prey 1, 2. This radular harpoon serves both as projectile and conduit for venom delivery. In the fish-hunting cone snail Conus catus, the radular harpoon is also utilized to tether the snail to its prey, rapidly paralyzed by neuroexcitatory peptides 2, 3. Effective prey capture in C. catus requires both fast-acting neurotoxins and a delivery system quick enough to exceed the prey fish’s rapid escape responses [4]. We report here that the cone snail’s prey strike is one of the fastest in the animal kingdom. A unique cellular latch mechanism prevents harpoon release until sufficient pressure builds and overcomes the forces of the latch, resulting in rapid acceleration into prey [2]. The radular harpoon then rapidly decelerates as its bulbous base reaches the end of the proboscis, a distensible hydrostatic skeleton extended toward the prey [2], with little slowing during prey impalement. The velocities achieved are the fastest movements of any mollusk and exceed previous estimates by over an order of magnitude [1].
  • Age-related clonal haemopoiesis is associated with increased epigenetic
    • Abstract: Publication date: 19 August 2019Source: Current Biology, Volume 29, Issue 16Author(s): Neil A. Robertson, Robert F. Hillary, Daniel L. McCartney, Maria Terradas-Terradas, Jonathan Higham, Duncan Sproul, Ian J. Deary, Kristina Kirschner, Riccardo E. Marioni, Tamir ChandraSummaryAge-related clonal haemopoiesis (ARCH) in healthy individuals was initially observed through an increased skewing in X-chromosome inactivation [1]. More recently, several groups reported that ARCH is driven by somatic mutations [2], with the most prevalent ARCH mutations being in the DNMT3A and TET2 genes, previously described as drivers of myeloid malignancies. ARCH is associated with an increased risk for haematological cancers [2]. ARCH also confers an increased risk for non-haematological diseases, such as cardiovascular disease, atherosclerosis, and chronic ischemic heart failure, for which age is a main risk factor 3, 4. Whether ARCH is linked to accelerated ageing has remained unexplored. The most accurate and commonly used tools to measure age acceleration are epigenetic clocks: they are based on age-related methylation differences at specific CpG sites [5]. Deviations from chronological age towards an increased epigenetic age have been associated with increased risk of earlier mortality and age-related morbidities 5, 6. Here we present evidence of accelerated epigenetic age in individuals with ARCH.
  • Fruit development and diversification
    • Abstract: Publication date: 19 August 2019Source: Current Biology, Volume 29, Issue 16Author(s): Yang Dong, Lars ØstergaardSummaryThe evolutionary success of angiosperms depends largely on the unique feature of producing fruits, which protect and nourish the seeds, and at maturity facilitate efficient seed dispersal. Fruits have long been an important energy source for humans, providing us with nutritious proteins and vitamins. Domestication of fruit and seed crops ignited the formation of modern civilisation during the Neolithic Revolution. In the past two decades, the fruit development process has been extensively studied in the model species Arabidopsis thaliana and related Brassicaceae species, and great advances have been made in dissecting the molecular circuit underlying patterning of the fruit into specific tissues. The aim of this Primer is to discuss the molecular network and the inter-connected hormonal signalling events in fruit patterning from an evolutionary and developmental point-of-view. An interesting theme emerging from the studies in leaves and fruits is that tissue polarity, as manifested by anisotropic growth, is tightly associated with local auxin distribution. We further highlight that changes in cell anisotropic growth, possibly directed by the formation of local auxin maxima, may explain fruit-shape diversification in the Brassicaceae.
  • Marmots
    • Abstract: Publication date: 19 August 2019Source: Current Biology, Volume 29, Issue 16Author(s): Walter Arnold
  • Richard McIntosh
    • Abstract: Publication date: 19 August 2019Source: Current Biology, Volume 29, Issue 16Author(s): Richard McIntosh
  • The reasons of sleep
    • Abstract: Publication date: 19 August 2019Source: Current Biology, Volume 29, Issue 16Author(s): Michael GrossSummaryMost animals sleep regularly, which is a puzzling behaviour, considering the risk of predation that many will be exposed to in a state of reduced alertness. Hypotheses linking the evolution of sleep to cognitive functions such as memory consolidation are undermined by growing evidence for sleep in very primitive animals, and thus a very early origin in evolution. Michael Gross reports.
  • Sleeping Unsafely Tucked in to Conserve Energy in a Nocturnal Migratory
    • Abstract: Publication date: 19 August 2019Source: Current Biology, Volume 29, Issue 16Author(s): Andrea Ferretti, Niels C. Rattenborg, Thomas Ruf, Scott R. McWilliams, Massimiliano Cardinale, Leonida FusaniSummaryEach spring and fall, millions of normally diurnal birds switch to migrating at night. Most of these are small songbirds (passerine) migrating long distances that need to alternate their migratory flights with refueling stopovers [1, 2], which can account for up to 80% of the total migratory period [3]. After a long nocturnal flight, these birds face the contrasting needs to recover sleep and refill depleted energy stores, all while vulnerable to predation [4, 5]. Here, we investigated how garden warblers at a Mediterranean stopover site modulate their sleep behavior in relation to their metabolic state. At night, garden warblers in poor metabolic condition sleep more and exhibit less migratory restlessness than birds in good condition do. In addition, rather than sleeping with their head facing forward, birds in poor condition prefer to sleep with their head turned and tucked in their feathers. We further show that sleep with the head tucked is associated with lower respiratory and metabolic rates and reduced heat loss mediated by hiding the head—the body part with the highest heat dissipation—under the feathers. However, the benefit of conserving energy while sleeping with the head tucked was countered by reduced anti-predator vigilance. Birds presented with a sound simulating the approach of a predator responded more slowly when the head was tucked than when it was untucked. Consequently, our study demonstrates that through changing their sleep position and intensity, migrating songbirds can negotiate a previously unknown trade-off between sleep-mediated energy conservation and anti-predatory vigilance.Graphical Graphical abstract for this article
  • Multiple Independent Origins of Apicomplexan-Like Parasites
    • Abstract: Publication date: Available online 15 August 2019Source: Current BiologyAuthor(s): Varsha Mathur, Martin Kolísko, Elisabeth Hehenberger, Nicholas A.T. Irwin, Brian S. Leander, Árni Kristmundsson, Mark A. Freeman, Patrick J. KeelingSummaryThe apicomplexans are a group of obligate animal pathogens that include Plasmodium (malaria), Toxoplasma (toxoplasmosis), and Cryptosporidium (cryptosporidiosis) [1]. They are an extremely diverse and specious group but are nevertheless united by a distinctive suite of cytoskeletal and secretory structures related to infection, called the apical complex, which is used to recognize and gain entry into animal host cells. The apicomplexans are also known to have evolved from free-living photosynthetic ancestors and retain a relict plastid (the apicoplast), which is non-photosynthetic but houses a number of other essential metabolic pathways [2]. Their closest relatives include a mix of both photosynthetic algae (chromerids) and non-photosynthetic microbial predators (colpodellids) [3]. Genomic analyses of these free-living relatives have revealed a great deal about how the alga-parasite transition may have taken place, as well as origins of parasitism more generally [4]. Here, we show that, despite the surprisingly complex origin of apicomplexans from algae, this transition actually occurred at least three times independently. Using single-cell genomics and transcriptomics from diverse uncultivated parasites, we find that two genera previously classified within the Apicomplexa, Piridium and Platyproteum, form separately branching lineages in phylogenomic analyses. Both retain cryptic plastids with genomic and metabolic features convergent with apicomplexans. These findings suggest a predilection in this lineage for both the convergent loss of photosynthesis and transition to parasitism, resulting in multiple lineages of superficially similar animal parasites.
  • A Tissue- and Temporal-Specific Autophagic Switch Controls Drosophila
           Pre-metamorphic Nutritional Checkpoints
    • Abstract: Publication date: Available online 15 August 2019Source: Current BiologyAuthor(s): Xueyang Pan, Thomas P. Neufeld, Michael B. O’ConnorSummaryProperly timed production of steroid hormones by endocrine tissues regulates juvenile-to-adult transitions in both mammals (puberty) and holometabolous insects (metamorphosis). Nutritional conditions influence the temporal control of the transition, but the mechanisms responsible are ill defined. Here we demonstrate that autophagy acts as an endocrine organ-specific, nutritionally regulated gating mechanism to help ensure productive metamorphosis in Drosophila. Autophagy in the endocrine organ is specifically stimulated by nutrient restriction at the early, but not the late, third-instar larva stage. The timing of autophagy induction correlates with the nutritional checkpoints, which inhibit precocious metamorphosis during nutrient restriction in undersized larvae. Suppression of autophagy causes dysregulated pupariation of starved larvae, which leads to pupal lethality, whereas forced autophagy induction results in developmental delay/arrest in well-fed animals. Induction of autophagy disrupts production of the steroid hormone ecdysone at the time of pupariation not by destruction of hormone biosynthetic capacity but rather by limiting the availability of the steroid hormone precursor cholesterol in the endocrine cells via a lipophagy mechanism. Interestingly, autophagy in the endocrine organ functions by interacting with the endolysosome system, yet shows multiple features not fully consistent with a canonical autophagy process. Taken together, our findings demonstrate an autophagy mechanism in endocrine cells that helps shape the nutritional checkpoints and guarantee a successful juvenile-to-adult transition in animals confronting nutritional stress.Graphical Graphical abstract for this article
  • Large-Scale Communication in the Human Brain Is Rhythmically Modulated
           through Alpha Coherence
    • Abstract: Publication date: Available online 15 August 2019Source: Current BiologyAuthor(s): Julio I. Chapeton, Rafi Haque, John H. Wittig, Sara K. Inati, Kareem A. ZaghloulSummaryRecent evidence has suggested that coherent neuronal oscillations may serve as a gating mechanism for flexibly modulating communication between brain regions. For this to occur, such oscillations should be robust and coherent between brain regions that also demonstrate time-locked correlations, with time delays that match the phase delays of the coherent oscillations. Here, by analyzing functional connectivity in both the time and frequency domains, we demonstrate that alpha oscillations satisfy these constraints and are well suited for modulating communication over large spatial scales in the human brain. We examine intracranial EEG in the human temporal lobe and find robust alpha oscillations that are coherent between brain regions with center frequencies that are consistent within each individual participant. Regions demonstrating coherent narrowband oscillations also exhibit time-locked broadband correlations with a consistent time delay, a requirement for an efficient communication channel. The phase delays of the coherent alpha oscillations match the time delays of the correlated components, and importantly, both broadband correlations and neuronal spiking activity are modulated by the phase of the oscillations. These results are specific to the alpha band and build upon emerging evidence suggesting that alpha oscillations may play an active role in cortical function. Our data therefore provide evidence that large-scale communication in the human brain may be rhythmically modulated by alpha oscillations.
  • Non-Crh Glutamatergic Neurons in Barrington’s Nucleus Control
           Micturition via Glutamatergic Afferents from the Midbrain and Hypothalamus
    • Abstract: Publication date: Available online 15 August 2019Source: Current BiologyAuthor(s): Anne M.J. Verstegen, Nataliya Klymko, Lin Zhu, John C. Mathai, Reina Kobayashi, Anne Venner, Rachel A. Ross, Veronique G. VanderHorst, Elda Arrigoni, Joel C. Geerling, Mark L. ZeidelSummaryLower urinary tract symptoms (LUTS) are exceptionally common and debilitating, and they are likely caused or exacerbated by dysfunction of neural circuits controlling bladder function. An incomplete understanding of neural control of bladder function limits our ability to clinically address LUTS. Barrington’s nucleus (Bar) provides descending control of bladder and sphincter function, and its glutamatergic neurons expressing corticotropin releasing hormone (BarCrh/Vglut2) are implicated in bladder control. However, it remains unclear whether this subset of Bar neurons is necessary for voiding, and the broader circuitry providing input to this control center remains largely unknown. Here, we examine the contribution to micturition behavior of BarCrh/Vglut2 neurons relative to the overall BarVglut2 population. First, we identify robust, excitatory synaptic input to Bar. Glutamatergic axons from the periaqueductal gray (PAG) and lateral hypothalamic area (LHA) intensely innervate and are functionally connected to Bar, and optogenetic stimulation of these axon terminals reliably provokes voiding. Similarly, optogenetic stimulation of BarVglut2 neurons triggers voiding, whereas stimulating the BarCrh/Vglut2 subpopulation causes bladder contraction, typically without voiding. Next, we genetically ablate either BarVglut2 or BarCrh/Vglut2 neurons and found that only BarVglut2 ablation replicates the profound urinary retention produced by conventional lesions in this region. Fiber photometry recordings reveal that BarVglut2 neuron activity precedes increased bladder pressure, while activity of BarCrh/Vglut2 is phase delayed. Finally, deleting Crh from Bar neurons has no effect on voiding and related bladder physiology. Our results help identify the circuitry that modulates Bar neuron activity and identify subtypes that may serve different roles in micturition.Graphical Graphical abstract for this article
  • Widespread Effects of Climate Change on Local Plant Diversity
    • Abstract: Publication date: Available online 15 August 2019Source: Current BiologyAuthor(s): Andrew J. Suggitt, Duncan G. Lister, Chris D. ThomasSummaryHuman activity has sent many measures of biodiversity into long-term decline, and there are suggestions that the sheer scale of this impact is sufficient to consider the modern era as a geological epoch of its own, known as “The Anthropocene” [1]. However, recent meta-analyses show that local alpha diversity is often stable or slightly increasing [2, 3, 4]. Here, we show that the local alpha diversity (species richness) of plants found in quadrats and transects has increased the most in cooler regions of the world that have experienced the highest absolute changes (i.e., changes in either direction) in climate. The greatest statistical support is for the effects of precipitation change. On average, alpha diversity declined slightly (−4.2% per decade) in the third of sites that experienced the lowest precipitation change but increased (+10.8% per decade) in the third of sites with the highest precipitation change. These results suggest that the “perturbation” of local communities during climatic transitions increases the average number of species, at least temporarily, an effect likely to remain important as climate change continues.
  • Area-Specific Mapping of Binocular Disparity across Mouse Visual Cortex
    • Abstract: Publication date: Available online 15 August 2019Source: Current BiologyAuthor(s): Alessandro La Chioma, Tobias Bonhoeffer, Mark HübenerSummaryDepth perception is a fundamental feature of many visual systems across species. It is relevant for crucial behaviors, like spatial orientation, prey capture, and predator detection. Binocular disparity, the difference between left and right eye images, is a powerful cue for depth perception, as it depends on an object’s distance from the observer [1, 2]. In primates, neurons sensitive to binocular disparity are found throughout most of the visual cortex, with distinct disparity tuning properties across primary and higher visual areas, suggesting specific roles of different higher areas for depth perception [1, 2, 3]. Mouse primary visual cortex (V1) has been shown to contain disparity-tuned neurons, similar to those found in other mammals [4, 5], but it is unknown how binocular disparity is processed beyond V1 and whether it is differentially represented in higher areas. Beyond V1, higher-order, lateromedial (LM) and rostrolateral (RL) areas contain the largest representation of the binocular visual field [6, 7], making them candidate areas for investigating downstream processing of binocular disparity in mouse visual cortex. In turn, comparison of disparity tuning across different mouse visual areas might help delineating their functional specializations, which are not well understood. We find clear differences in neurons’ preferred disparities across areas, suggesting that higher visual area RL is specialized for encoding visual stimuli very close to the mouse. Moreover, disparity preference is related to visual field elevation, likely reflecting an adaptation to natural image statistics. Our results reveal ethologically relevant areal specializations for binocular disparity processing across mouse visual cortex.
  • Transient Activations of Rac1 at the Lamellipodium Tip Trigger Membrane
    • Abstract: Publication date: Available online 15 August 2019Source: Current BiologyAuthor(s): Amine Mehidi, Olivier Rossier, Matthias Schaks, Anaël Chazeau, Fabien Binamé, Amanda Remorino, Mathieu Coppey, Zeynep Karatas, Jean-Baptiste Sibarita, Klemens Rottner, Violaine Moreau, Grégory GiannoneSummaryThe spatiotemporal coordination of actin regulators in the lamellipodium determines the dynamics and architecture of branched F-actin networks during cell migration. The WAVE regulatory complex (WRC), an effector of Rac1 during cell protrusion, is concentrated at the lamellipodium tip. Thus, activated Rac1 should operate at this location to activate WRC and trigger membrane protrusion. Yet correlation of Rho GTPase activation with cycles of membrane protrusion previously revealed complex spatiotemporal patterns of Rac1 and RhoA activation in the lamellipodium. Combining single protein tracking (SPT) and super-resolution imaging with loss- or gain-of-function mutants of Rho GTPases, we show that Rac1 immobilizations at the lamellipodium tip correlate with its activation, in contrast to RhoA. Using Rac1 effector loop mutants and wild-type versus mutant variants of WRC, we show that selective immobilizations of activated Rac1 at the lamellipodium tip depend on effector binding, including WRC. In contrast, wild-type Rac1 only displays slower diffusion at the lamellipodium tip, suggesting transient activations. Local optogenetic activation of Rac1, triggered by membrane recruitment of Tiam1, shows that Rac1 activation must occur close to the lamellipodium tip and not behind the lamellipodium to trigger efficient membrane protrusion. However, coupling tracking with optogenetic activation of Rac1 demonstrates that diffusive properties of wild-type Rac1 are unchanged despite enhanced lamellipodium protrusion. Taken together, our results support a model whereby transient activations of Rac1 occurring close to the lamellipodium tip trigger WRC binding. This short-lived activation ensures a local and rapid control of Rac1 actions on its effectors to trigger actin-based protrusion.Graphical Graphical abstract for this article
  • Slower Binocular Rivalry in the Autistic Brain
    • Abstract: Publication date: Available online 15 August 2019Source: Current BiologyAuthor(s): Alina Spiegel, Jeff Mentch, Amanda J. Haskins, Caroline E. RobertsonSummaryAutism has traditionally been regarded as a disorder of the social brain. Recent reports of differences in visual perception have challenged this notion, but little evidence for altered visual processing in the autistic brain exists. We have previously observed slower behaviorally reported rates of a basic visual phenomenon, binocular rivalry, in autism [1, 2]. During rivalry, two images—one presented to each eye—vie for awareness, alternating back and forth in perception. This competition is modeled to rely, in part, on the balance of excitation and inhibition in visual cortex [3, 4, 5, 6, 7, 8], which may be altered in autism [2, 9, 10, 11, 12, 13, 14]. Yet direct neural evidence for this potential marker of excitation/inhibition (E/I) balance in autism is lacking. Here, we report a striking alteration in the neural dynamics of binocular rivalry in individuals with autism. Participants viewed true and simulated frequency-tagged binocular rivalry displays while steady-state visually evoked potentials (SSVEPs) were measured over occipital cortex using electroencephalography (EEG). First, we replicate our prior behavioral findings of slower rivalry and reduced perceptual suppression in individuals with autism compared with controls. Second, we provide direct neural evidence for slower rivalry in autism compared with controls, which strongly predicted individuals’ behavioral switch rates. Finally, using neural data alone, we were able to predict autism symptom severity (ADOS) and correctly classify individuals’ diagnostic status (autistic versus control; 87% accuracy). These findings clearly implicate atypical visual processing in the neurobiology of autism. Down the road, this paradigm may serve as a non-verbal marker of autism for developmental and cross-species research.
  • Transient Internalization and Microtubule-Dependent Trafficking of a
           Ciliary Signaling Receptor from the Plasma Membrane to the Cilium
    • Abstract: Publication date: Available online 15 August 2019Source: Current BiologyAuthor(s): Peeyush Ranjan, Mayanka Awasthi, William J. SnellSummaryCilia are ancient organelles used by unicellular and multicellular organisms not only for motility but also to receive and respond to multiple environmental cues, including light, odorants, morphogens, growth factors, and contact with cilia of other cells. Much is known about the cellular mechanisms that deliver membrane proteins to cilia during ciliogenesis. Execution of a ciliary signaling pathway, however, can critically depend on rapid alterations in the receptor composition of the cilium itself, and our understanding of the mechanisms that underlie these rapid, regulated alterations remains limited [1, 2, 3, 4, 5, 6]. In the bi-ciliated, unicellular alga Chlamydomonas reinhardtii, interactions between cilia of mating type plus and mating type minus gametes mediated by adhesion receptors SAG1 and SAD1 activate a ciliary signaling pathway [7]. In response, a large, inactive pool of SAG1 on the plasma membrane of plus gametes rapidly becomes enriched in the peri-ciliary membrane and enters the cilia to become active and maintain and enhance ciliary adhesion and signaling [8, 9, 10, 11, 12, 13, 14]. Ciliary entry per se of SAG1 is independent of anterograde intraflagellar transport (IFT) [13], but the rapid apical enrichment requires cytoplasmic microtubules and the retrograde IFT motor, dynein 1b [14]. Whether the receptors move laterally within the plasma membrane or transit internally during redistribution is unknown. Here, in coupled immunolocalization/biochemical studies on SAG1, we show that, within minutes after gamete activation is initiated, cell-surface SAG1 is internalized, associates with an apico-basally polarized array of cytoplasmic microtubules, and returns to the cell surface at a peri-ciliary staging area for entry into cilia.
  • Environmental Programming of Adult Foraging Behavior in
           C. elegans
    • Abstract: Publication date: Available online 15 August 2019Source: Current BiologyAuthor(s): Sreeparna Pradhan, Sabrina Quilez, Kai Homer, Michael HendricksSummaryForaging strategies should be tuned to the expected distribution of resources in the environment. Tuning can occur over generations and lead to genetic differences in innate foraging behavior or over shorter timescales within an individual’s lifespan. Both genetically encoded and experience-based strategies are implemented by neural circuits that respond to environmental cues and track internal states. Caenorhabditis elegans exhibit both between-strain genetic differences and within-strain plasticity in foraging. In individuals, changes in foraging are usually short term and based on recent experience. Here, we tested whether developmental experience could permanently alter foraging. We found that, in most wild strains, early-life starvation led to “cautious” foraging strategies, in which exploration is reduced, and these behavioral changes are associated with altered dynamics in a locomotory circuit. Possessing either the derived (domestication-associated) or ancestral allele of the neuroglobin glb-5 determines foraging plasticity. Overall, we show that C. elegans exhibit adaptive developmental plasticity that affects multiple aspects of foraging behavior and leads to changes in a core navigation circuit and that innate foraging traits and plasticity in those traits are genetically separable.
  • The Most Extensive Devonian Fossil Forest with Small Lycopsid Trees
           Bearing the Earliest Stigmarian Roots
    • Abstract: Publication date: Available online 8 August 2019Source: Current BiologyAuthor(s): Deming Wang, Min Qin, Le Liu, Lu Liu, Yi Zhou, Yingying Zhang, Pu Huang, Jinzhuang Xue, Shihui Zhang, Meicen MengSummarySince the Late Paleozoic, forests have become distributed worldwide and significantly changed the Earth’s climate and landscapes, but the record of forests is rare in the Devonian (419–359 Ma in age) when they first appeared. From the Upper Devonian (Famennian with the age of 372–359 Ma) of Xinhang, Anhui, China, we report a very large in situ forest, which includes locally dense stands of lycopsid plants. The Xinhang forest is monospecific with a small tree lycopsid Guangdedendron gen. nov., probably dioecious with monocarpic reproduction. The plant shows the earliest stigmarian rooting system typical of giant tree lycopsids dominating Carboniferous forests. It colonizes coastal clastic wetlands that were influenced by floods. This significantly increases the paleogeographical coverage of in situ Devonian forests, and contributes to our understanding of atmospheric CO2 decline and coastal consolidation.
  • Maintenance of High Genome Integrity over Vegetative Growth in the
           Fairy-Ring Mushroom Marasmius oreades
    • Abstract: Publication date: Available online 8 August 2019Source: Current BiologyAuthor(s): Markus Hiltunen, Magdalena Grudzinska-Sterno, Ola Wallerman, Martin Ryberg, Hanna JohannessonSummaryMost mutations in coding regions of the genome are deleterious, causing selection to favor mechanisms that minimize the mutational load over time [1, 2, 3, 4, 5]. DNA replication during cell division is a major source of new mutations. It is therefore important to limit the number of cell divisions between generations, particularly for large and long-lived organisms [6, 7, 8, 9]. The germline cells of animals and the slowly dividing cells in plant meristems are adaptations to control the number of mutations that accumulate over generations [9, 10, 11]. Fungi lack a separated germline while harboring species with very large and long-lived individuals that appear to maintain highly stable genomes within their mycelia [8, 12, 13]. Here, we studied genomic mutation accumulation in the fairy-ring mushroom Marasmius oreades. We generated a chromosome-level genome assembly using a combination of cutting-edge DNA sequencing technologies and re-sequenced 40 samples originating from six individuals of this fungus. The low number of mutations recovered in the sequencing data suggests the presence of an unknown mechanism that works to maintain extraordinary genome integrity over vegetative growth in M. oreades. The highly structured growth pattern of M. oreades allowed us to estimate the number of cell divisions leading up to each sample [14, 15], and from this data, we infer an incredibly low per mitosis mutation rate (3.8 × 10−12 mutations per site and cell division) as one of several possible explanations for the low number of identified mutations.
  • Genomic Evidence for Local Adaptation of Hunter-Gatherers to the African
    • Abstract: Publication date: Available online 8 August 2019Source: Current BiologyAuthor(s): Marie Lopez, Jeremy Choin, Martin Sikora, Katherine Siddle, Christine Harmant, Helio A. Costa, Martin Silvert, Patrick Mouguiama-Daouda, Jean-Marie Hombert, Alain Froment, Sylvie Le Bomin, George H. Perry, Luis B. Barreiro, Carlos D. Bustamante, Paul Verdu, Etienne Patin, Lluís Quintana-MurciSummaryAfrican rainforests support exceptionally high biodiversity and host the world’s largest number of active hunter-gatherers [1, 2, 3]. The genetic history of African rainforest hunter-gatherers and neighboring farmers is characterized by an ancient divergence more than 100,000 years ago, together with recent population collapses and expansions, respectively [4, 5, 6, 7, 8, 9, 10, 11, 12]. While the demographic past of rainforest hunter-gatherers has been deeply characterized, important aspects of their history of genetic adaptation remain unclear. Here, we investigated how these groups have adapted—through classic selective sweeps, polygenic adaptation, and selection since admixture—to the challenging rainforest environments. To do so, we analyzed a combined dataset of 566 high-coverage exomes, including 266 newly generated exomes, from 14 populations of rainforest hunter-gatherers and farmers, together with 40 newly generated, low-coverage genomes. We find evidence for a strong, shared selective sweep among all hunter-gatherer groups in the regulatory region of TRPS1—primarily involved in morphological traits. We detect strong signals of polygenic adaptation for height and life history traits such as reproductive age; however, the latter appear to result from pervasive pleiotropy of height-associated genes. Furthermore, polygenic adaptation signals for functions related to responses of mast cells to allergens and microbes, the IL-2 signaling pathway, and host interactions with viruses support a history of pathogen-driven selection in the rainforest. Finally, we find that genes involved in heart and bone development and immune responses are enriched in both selection signals and local hunter-gatherer ancestry in admixed populations, suggesting that selection has maintained adaptive variation in the face of recent gene flow from farmers.
  • HLH-2/E2A Expression Links Stochastic and Deterministic Elements of a Cell
           Fate Decision during C. elegans Gonadogenesis
    • Abstract: Publication date: Available online 8 August 2019Source: Current BiologyAuthor(s): Michelle A. Attner, Wolfgang Keil, Justin M. Benavidez, Iva GreenwaldSummaryStochastic mechanisms diversify cell fate in organisms ranging from bacteria to humans [1, 2, 3, 4]. In the anchor cell/ventral uterine precursor cell (AC/VU) fate decision during C. elegans gonadogenesis, two “α cells,” each with equal potential to be an AC or a VU, interact via LIN-12/Notch and its ligand LAG-2/DSL [5, 6]. This LIN-12/Notch-mediated interaction engages feedback mechanisms that amplify a stochastic initial difference between the two α cells, ensuring that the cell with higher lin-12 activity becomes the VU while the other becomes the AC [7, 8, 9]. The initial difference between the α cells was originally envisaged as a random imbalance from “noise” in lin-12 expression/activity [6]. However, subsequent evidence that the relative birth order of the α cells biases their fates suggested other factors may be operating [7]. Here, we investigate the nature of the initial difference using high-throughput lineage analysis [10]; GFP-tagged endogenous LIN-12, LAG-2, and HLH-2, a conserved transcription factor that orchestrates AC/VU development [7, 11]; and tissue-specific hlh-2 null alleles. We identify two stochastic elements: relative birth order, which largely originates at the beginning of the somatic gonad lineage three generations earlier, and onset of HLH-2 expression, such that the α cell whose parent expressed HLH-2 first is biased toward the VU fate. We find that these elements are interrelated, because initiation of HLH-2 expression is linked to the birth of the parent cell. Finally, we provide a potential deterministic mechanism for the HLH-2 expression bias by showing that hlh-2 is required for LIN-12 expression in the α cells.Graphical Graphical abstract for this article
  • Rapid Coral Decay Is Associated with Marine Heatwave Mortality Events on
    • Abstract: Publication date: Available online 8 August 2019Source: Current BiologyAuthor(s): William P. Leggat, Emma F. Camp, David J. Suggett, Scott F. Heron, Alexander J. Fordyce, Stephanie Gardner, Lachlan Deakin, Michael Turner, Levi J. Beeching, Unnikrishnan Kuzhiumparambil, C. Mark Eakin, Tracy D. AinsworthSummarySevere marine heatwaves have recently become a common feature of global ocean conditions due to a rapidly changing climate [1, 2]. These increasingly severe thermal conditions are causing an unprecedented increase in the frequency and severity of mortality events in marine ecosystems, including on coral reefs [3]. The degradation of coral reefs will result in the collapse of ecosystem services that sustain over half a billion people globally [4, 5]. Here, we show that marine heatwave events on coral reefs are biologically distinct to how coral bleaching has been understood to date, in that heatwave conditions result in an immediate heat-induced mortality of the coral colony, rapid coral skeletal dissolution, and the loss of the three-dimensional reef structure. During heatwave-induced mortality, the coral skeletons exposed by tissue loss are, within days, encased by a complex biofilm of phototrophic microbes, whose metabolic activity accelerates calcium carbonate dissolution to rates exceeding accretion by healthy corals and far greater than has been documented on reefs under normal seawater conditions. This dissolution reduces the skeletal density and hardness and increases porosity. These results demonstrate that severe-heatwave-induced mortality events should be considered as a distinct biological phenomenon from bleaching events on coral reefs. We also suggest that such heatwave mortality events, and rapid reef decay, will become more frequent as the intensity of marine heatwaves increases and provides further compelling evidence for the need to mitigate climate change and instigate actions to reduce marine heatwaves.Graphical Graphical abstract for this article
  • A Dynamic Optical Signal in a Nocturnal Moth
    • Abstract: Publication date: Available online 8 August 2019Source: Current BiologyAuthor(s): Jennifer L. Kelley, Nikolai J. Tatarnic, Gerd E. Schröder-Turk, John A. Endler, Bodo D. WiltsSummaryThe wings of butterflies and moths generate some of the most spectacular visual displays observed in nature [1, 2, 3]. Particularly striking effects are seen when light interferes with nanostructure materials in the wing scales, generating bright, directional colors that often serve as dynamic visual signals [4]. Structural coloration is not known in night-flying Lepidoptera, yet here we show a highly unusual form of wing coloration in a nocturnal, sexually dimorphic moth, Eudocima materna (Noctuidae). Males feature three dark wing patches on the dorsal forewings, and the apparent size of these patches strongly varies depending on the angle of the wing to the viewer. These optical special effects are generated using specialized wing scales that are tilted on the wing and behave like mirrors. At near-normal incidence of light, these “mirror scales” act as thin-film reflectors to produce a sparkly effect, but when light is incident at ∼20°–30° from normal, the reflectance spectrum is dominated by the diffuse scattering of the underlying, black melanin-containing scales, causing a shape-shifting effect. The strong sexual dimorphism in the arrangement and architecture of the scale nanostructures suggests that these patterns might function for sexual signaling. Flickering of the male’s wings would yield a flashing, supernormal visual stimulus [5] to a viewer located 20°–30° away from the vertical, while being invisible to a viewer directly above the animal. Our findings reveal a novel use of structural coloration in nature that yields a dynamic, time-dependent achromatic optical signal that may be optimized for visual signaling in dim light.Graphical Graphical abstract for this article
  • The Taiman Transcriptional Coactivator Engages Toll Signals to Promote
           Apoptosis and Intertissue Invasion in Drosophila
    • Abstract: Publication date: Available online 8 August 2019Source: Current BiologyAuthor(s): Phil K. Byun, Can Zhang, Bing Yao, Joanna Wardwell-Ozgo, Douglas Terry, Peng Jin, Ken MobergSummaryThe Drosophila Taiman (Tai) protein is homologous to the human steroid-receptor coactivators SRC1–3 and activates transcription in complex with the 20-hydroxyecdysone (20E) receptor (EcR). Tai has roles in intestinal homeostasis, germline maintenance, cell motility, and proliferation through interactions with EcR and the coactivator Yorkie (Yki). Tai also promotes invasion of tumor cells in adjacent organs, but this pro-invasive mechanism is undefined. Here, we show that Tai expression transforms sessile pupal wing cells into an invasive mass that penetrates the adjacent thorax during a period of high 20E. Candidate analysis confirms a reliance on elements of the 20E and Hippo pathways, such as Yki and the Yki-Tai target dilp8. Screening the Tai-induced wing transcriptome detects enrichment for innate immune factors, including the Spätzle (Spz) family of secreted Toll ligands that induce apoptosis during cell competition. Tai-expressing wing cells induce immune signaling and apoptosis among adjacent thoracic cells, and genetic reduction of spz, Toll, or the rpr/hid/grim pro-apoptotic factors each suppresses invasion, suggesting an intercellular Spz-Toll circuit supports killing-mediated invasion. Modeling these interactions in larval epithelia confirms that Tai kills neighboring cells via a mechanism involving Toll, Spz factors, and the Spz inhibitor Necrotic. Tai-expressing cells evade death signals by repressing the immune deficiency (IMD) pathway, which operates in parallel to Toll to control nuclear factor κB (NF-κB) activity and independently regulates JNK activity. In sum, these findings suggest that Tai promotes competitive cell killing via Spz-Toll and that this killing mechanism supports pathologic intertissue invasion in Drosophila.Graphical Graphical abstract for this article
  • Modality-Specific Circuits for Skylight Orientation in the Fly Visual
    • Abstract: Publication date: Available online 8 August 2019Source: Current BiologyAuthor(s): Gizem Sancer, Emil Kind, Haritz Plazaola-Sasieta, Jana Balke, Tuyen Pham, Amr Hasan, Lucas O. Münch, Maximilien Courgeon, Thomas F. Mathejczyk, Mathias F. WernetSummaryIn the fly optic lobe, ∼800 highly stereotypical columnar microcircuits are arranged retinotopically to process visual information. Differences in cellular composition and synaptic connectivity within functionally specialized columns remain largely unknown. Here, we describe the cellular and synaptic architecture in medulla columns located downstream of photoreceptors in the dorsal rim area (DRA), where linearly polarized skylight is detected for guiding orientation responses. We show that only in DRA medulla columns both R7 and R8 photoreceptors target to the bona fide R7 target layer where they form connections with previously uncharacterized, modality-specific Dm neurons: two morphologically distinct DRA-specific cell types (termed Dm-DRA1 and Dm-DRA2) stratify in separate sublayers and exclusively contact polarization-sensitive DRA inputs, while avoiding overlaps with color-sensitive Dm8 cells. Using the activity-dependent GRASP and trans-Tango techniques, we confirm that DRA R7 cells are synaptically connected to Dm-DRA1, whereas DRA R8 form synapses with Dm-DRA2. Finally, using live imaging of ingrowing pupal photoreceptor axons, we show that DRA R7 and R8 termini reach layer M6 sequentially, thus separating the establishment of different synaptic connectivity in time. We propose that a duplication of R7→Dm circuitry in DRA ommatidia serves as an ideal adaptation for detecting linearly polarized skylight using orthogonal e-vector analyzers.Graphical Graphical abstract for this article
  • Mechanical Stabilization of the Glandular Acinus by Linker of
           Nucleoskeleton and Cytoskeleton Complex
    • Abstract: Publication date: Available online 8 August 2019Source: Current BiologyAuthor(s): Qiao Zhang, Vani Narayanan, Keeley L. Mui, Christopher S. O’Bryan, Ruthellen H. Anderson, Birendra KC, Jolene I. Cabe, Kevin B. Denis, Susumu Antoku, Kyle J. Roux, Richard B. Dickinson, Thomas E. Angelini, Gregg G. Gundersen, Daniel E. Conway, Tanmay P. LeleSummaryThe nucleoskeleton and cytoskeleton are important protein networks that govern cellular behavior and are connected together by the linker of nucleoskeleton and cytoskeleton (LINC) complex. Mutations in LINC complex components may be relevant to cancer, but how cell-level changes might translate into tissue-level malignancy is unclear. We used glandular epithelial cells in a three-dimensional culture model to investigate the effect of perturbations of the LINC complex on higher order cellular architecture. We show that inducible LINC complex disruption in human mammary epithelial MCF-10A cells and canine kidney epithelial MDCK II cells mechanically destabilizes the acinus. Lumenal collapse occurs because the acinus is unstable to increased mechanical tension that is caused by upregulation of Rho-kinase-dependent non-muscle myosin II motor activity. These findings provide a potential mechanistic explanation for how disruption of LINC complex may contribute to a loss of tissue structure in glandular epithelia.
  • Mating-System Evolution: All Roads Lead to Selfing
    • Abstract: Publication date: 5 August 2019Source: Current Biology, Volume 29, Issue 15Author(s): Sheng Sun, Xiaorong Lin, Marco A. Coelho, Joseph HeitmanSummaryFungi reproduce via both heterothallic outcrossing and homothallic selfing modes, and transitions between the two are common throughout the tree of life. A new study reports that the transition from heterothallism to homothallism is common and has repeatedly punctuated the evolutionary trajectory across a major lineage of the fungal kingdom.
  • Retraction Notice to: The Negative Association between Religiousness and
           Children’s Altruism across the World
    • Abstract: Publication date: 5 August 2019Source: Current Biology, Volume 29, Issue 15Author(s): Jean Decety, Jason M. Cowell, Kang Lee, Randa Mahasneh, Susan Malcolm-Smith, Bilge Selcuk, Xinyue Zhou
  • Deep Macroevolutionary Impact of Humans on New Zealand’s Unique
    • Abstract: Publication date: 5 August 2019Source: Current Biology, Volume 29, Issue 15Author(s): Luis Valente, Rampal S. Etienne, Juan C. Garcia-R.SummaryIslands are at the frontline of the anthropogenic extinction crisis [1]. A vast number of island birds have gone extinct since human colonization [2], and an important proportion is currently threatened with extinction [3]. While the number of lost or threatened avian species has often been quantified [4], the macroevolutionary consequences of human impact on island biodiversity have rarely been measured [5]. Here, we estimate the amount of evolutionary time that has been lost or is under threat due to anthropogenic activity in a classic example, New Zealand. Half of its bird taxa have gone extinct since humans arrived [6, 7] and many are threatened [8], including lineages forming highly distinct branches in the avian tree of life [9, 10, 11]. Using paleontological and ancient DNA information, we compiled a dated phylogenetic dataset for New Zealand’s terrestrial avifauna. We extend the method DAISIE developed for island biogeography [12] to allow for the fact that many of New Zealand’s birds are evolutionarily isolated and use it to estimate natural rates of speciation, extinction, and colonization. Simulating under a range of human-induced extinction scenarios, we find that it would take approximately 50 million years (Ma) to recover the number of species lost since human colonization of New Zealand and up to 10 Ma to return to today’s species numbers if currently threatened species go extinct. This study puts into macroevolutionary perspective the impact of humans in an isolated fauna and reveals how conservation decisions we take today will have repercussions for millions of years.
  • Causes and Consequences of Pleistocene Megafaunal Extinctions as Revealed
           from Rancho La Brea Mammals
    • Abstract: Publication date: 5 August 2019Source: Current Biology, Volume 29, Issue 15Author(s): Larisa R.G. DeSantis, Jonathan M. Crites, Robert S. Feranec, Kena Fox-Dobbs, Aisling B. Farrell, John M. Harris, Gary T. Takeuchi, Thure E. CerlingSummaryThe fossils preserved in the Rancho La Brea “tar” seeps in southern California span the past ∼50,000 years and provide a rare opportunity to assess the ecology of predators (e.g., the American lion, sabertooth cats, cougars, dire wolves, gray wolves, and coyotes), including clarifying the causes and consequences of the terminal Pleistocene extinction event. Here, a multi-proxy approach elucidates dietary responses of carnivorans to changing climates and megafaunal extinctions. Using sample sizes that are unavailable anywhere else in the world, including hundreds of carnivoran and herbivore specimens, we clarify the paleobiology of the extinct sabertooth cats and dire wolves—overturning the idea that they heavily competed for similar prey. Canids (especially the dire wolf) consumed prey from more open environments than felids, demonstrating minimal competition for prey throughout the latest Pleistocene and largely irrespective of changing climates, including just prior to their extinction. Coyotes experienced a dramatic shift in dietary behavior toward increased carcass utilization and the consumption of forest resources (prey and/or plant resources) after the terminal Pleistocene megafaunal extinction. Extant predators’ ability to effectively hunt smaller prey and/or utilize carcasses may have been a key to their survival, especially after a significant reduction in megafaunal prey resources. Collectively, these data suggest that dietary niches of carnivorans are not always static and can instead be substantially affected by the removal of top predators and abundant prey resources.
  • Multiple Influences of Mechanical Forces on Cell Competition
    • Abstract: Publication date: 5 August 2019Source: Current Biology, Volume 29, Issue 15Author(s): Alexis Matamoro-Vidal, Romain LevayerCell competition is a widespread process leading to the expansion of one cell population through the elimination and replacement of another. A large number of genetic alterations can lead to either competitive elimination of the mutated population or expansion of the mutated cells through the elimination of the neighbouring cells. Several processes have been proposed to participate in the preferential elimination of one cell population, including competition for limiting extracellular pro-survival factors, communication through direct cell–cell contact, or differential sensitivity to mechanical stress. Recent quantitative studies of cell competition have also demonstrated the strong impact of the shape of the interfaces between the two populations. Here, we discuss the direct and indirect contribution of mechanical cues to cell competition, where they act either as modulators of competitive interactions or as direct drivers of cell elimination. We first discuss how mechanics can regulate contact-dependent and diffusion-based competition by modulating the shape of the interface between the two populations. We then describe the direct contribution of mechanical stress to cell elimination and competition for space. Finally, we discuss how mechanical feedback also influences compensatory growth and triggers preferential expansion of one population.
  • Cellular Organization: Bulk Actin Network Flows Drive Ooplasm Segregation
    • Abstract: Publication date: 5 August 2019Source: Current Biology, Volume 29, Issue 15Author(s): Niv Ierushalmi, Kinneret KerenActin networks in the bulk cytoplasm, rather than cortical dynamics, drive ooplasm segregation in zebrafish oocytes. A contracting actin network drags the ooplasm toward the animal pole, while ‘comet tails’ push the yolk granules in the opposite direction.
  • Development: How Tadpoles ROC Tail Regeneration
    • Abstract: Publication date: 5 August 2019Source: Current Biology, Volume 29, Issue 15Author(s): Garrett S. Dunlap, Jessica L. WhitedSummarySpecialized epidermal cells are essential for the complex tissue regeneration required to replace tails and limbs, but their exact identities and molecular roles remain murky. Recent work in Xenopus has identified an epidermal cell population critical for tail regeneration, providing intriguing new directions for the field.
  • Evolution: The Flowering of Land Plant Evolution
    • Abstract: Publication date: 5 August 2019Source: Current Biology, Volume 29, Issue 15Author(s): Philip DonoghueTwo new studies that consider the timing of origin of angiosperms are poles apart in their estimates. However, their partisan molecular and palaeontological perspectives may hold the key to establishing a unified evolutionary timescale for flowering plants.
  • Perceptual Prediction: Rapidly Making Sense of a Noisy World
    • Abstract: Publication date: 5 August 2019Source: Current Biology, Volume 29, Issue 15Author(s): Clare Press, Daniel YonPrior knowledge shapes what we perceive. A new brain stimulation study suggests that this perceptual shaping is achieved by changes in sensory brain regions before the input arrives, with common mechanisms operating across different sensory areas.
  • Maternal Inheritance: Longevity Programs Nourish Progeny via Yolk
    • Abstract: Publication date: 5 August 2019Source: Current Biology, Volume 29, Issue 15Author(s): Robert H. Dowen, Shawn AhmedSummaryEpigenetic effects can be mediated by changes in chromatin state that are transmitted from parent to child via gametes, but support is gathering for maternal yolk, which is deposited into ooctyes, as an extranuclear epigenetic factor that can contribute to phenotypic plasticity across generations in Caenorhabditis elegans.
  • Genetics: Segregation of Mitochondrial Genomes in the Germline
    • Abstract: Publication date: 5 August 2019Source: Current Biology, Volume 29, Issue 15Author(s): Carlos T. MoraesSummaryMitochondrial genomes are present in hundreds of copies per cell. Recent work now reports the levels of inheritance of mtDNA heteroplasmy in humans and also explores mechanisms that restrict the inheritance of deleterious mtDNA variants in the Drosophila female germline.
  • Conservation: Monitoring Elephant Poaching to Prevent a Population Crash
    • Abstract: Publication date: 5 August 2019Source: Current Biology, Volume 29, Issue 15Author(s): Samuel K. Wasser, Kathleen S. Gobush
  • Plant Cell Biology: UVA on Guard
    • Abstract: Publication date: 5 August 2019Source: Current Biology, Volume 29, Issue 15Author(s): Carl K.-Y. NgSummaryStomata are pores on the surfaces of leaves that function to regulate loss of water for cooling while at the same time facilitating the uptake of carbon dioxide for photosynthesis. A new study shows how stomatal guard cells can sense ultraviolet-A radiation via cGMP signalling to inhibit the opening of these pores in order to reduce transpirational water loss in the short-term.
  • Visual Perception: Monovision Can Bias the Apparent Depth of Moving
    • Abstract: Publication date: 5 August 2019Source: Current Biology, Volume 29, Issue 15Author(s): Jenny C.A. ReadSummary‘Monovision’ — using one eye for near work and one for distance — is a common alternative to reading glasses. New work shows that monovision can cause the distance of moving objects to be misestimated, with potentially serious consequences.
  • The mitochondrial and chloroplast genomes of the green alga Haematococcus
           are made up of nearly identical repetitive sequences
    • Abstract: Publication date: 5 August 2019Source: Current Biology, Volume 29, Issue 15Author(s): Xi Zhang, Nicholas Bauman, Rob Brown, Toby H. Richardson, Srividya Akella, Elizabeth Hann, Robert Morey, David Roy SmithSummaryThe chlamydomonadalean green alga Haematococcus lacustris (strain UTEX 2505) has the largest chloroplast genome on record: 1352 kb with ∼90% non-coding DNA 1, 2. But what of the mitochondrial genome' Here we present sequencing, assembly, and analysis of the mitogenome that shows that it, too, is extremely expanded. What’s more, the same repetitive elements have spread throughout the mitochondrial and chloroplast (or plastid) DNA (mtDNA and ptDNA, respectively), resulting in the situation whereby these two distinct organelle genomes are made up of nearly identical sequences.
  • Response to Garcia and Dunn
    • Abstract: Publication date: 5 August 2019Source: Current Biology, Volume 29, Issue 15Author(s): Sven Grawunder, Catherine Crockford, Ammie.K. Kalan, Zanna Clay, Alexander Stoessel, Gottfried HohmannSummaryGarcia and Dunn [1] raise some interesting and valuable points regarding our recent paper in Current Biology [2]. As Garcia and Dunn [1] point out, cross-species variation in vocal and anatomical relations allows for the identification of relevant outliers from the body size — fundamental frequency (f0) regression. However, this depends on the premise that the chosen or available f0 and body size values are typical of the species. A motivation for our study [2] was in part to improve the accuracy of such estimates by providing more data per species compared to previous studies. We address each point of their critique by controlling for cross-species body size variation using body weights for chimpanzees (Pan troglodytes) and bonobos (Pan paniscus), addressing potential call variation in different subspecies of Pan troglodytes, measuring minimum f0 as well as maximum f0 and possible effects caused by different larynx fixation methods.
  • No evidence that maximum fundamental frequency reflects selection for
           signal diminution in bonobos
    • Abstract: Publication date: 5 August 2019Source: Current Biology, Volume 29, Issue 15Author(s): Maxime Garcia, Jacob C. DunnSummaryAcoustic allometry consists of looking at how an organism’s body size scales with the characteristics of its vocalizations. A typical finding based on this framework is that across mammals body size is reflected in the fundamental frequency (fo) of vocalizations, whereby lower fo indicates larger body size [1]. This relationship holds owing to the fact that vocal fold length generally scales with body size [2]. Cross-species comparisons allow for the identification of interesting outliers from the body size–f0 regression [3]. Such cases are of particular relevance as they can provide insight into the selective forces potentially driving deviations from standard allometric principles [2]. In a recent study in Current Biology, Grawunder et al. [4] argue that selective pressure for higher f0 has led to the evolution of shorter vocal folds in bonobos than in chimpanzees. Thus, they claim, vocal fold length has evolved independently of body size in bonobos for the purposes of signal diminution (i.e., reducing the impression of body size that they advertise through their calls). However, considering both the existing literature and their own data, this conclusion does not appear to be supported for several reasons.
  • Cephalopod cognition
    • Abstract: Publication date: 5 August 2019Source: Current Biology, Volume 29, Issue 15Author(s): Alexandra K. Schnell, Nicola S. ClaytonSummaryCephalopods have captivated the minds of scientists for thousands of years, dating back to approximately 330 BC when Aristotle became fascinated by their ability to rapidly change colour. This remarkable ability, however, is not the only aspect of cephalopod behaviour that has garnered attention from the scientific community. The soft-bodied cephalopods (henceforth cephalopods), namely octopus, cuttlefish, and squid, are widely considered to be the most cognitively advanced group of invertebrates. They possess highly developed perceptual, memory, and spatial learning abilities and are also capable of intriguing feats of behaviour that appear to indicate complex cognition.
  • Two-component systems
    • Abstract: Publication date: 5 August 2019Source: Current Biology, Volume 29, Issue 15Author(s): Nicolas Papon, Ann M. Stock
  • Cuckoo catfish
    • Abstract: Publication date: 5 August 2019Source: Current Biology, Volume 29, Issue 15Author(s): Martin Reichard
  • Dinosaurs: what discoveries are truly revolutionary'
    • Abstract: Publication date: 5 August 2019Source: Current Biology, Volume 29, Issue 15Author(s): Zhonghe Zhou
  • Geert Kops
    • Abstract: Publication date: 5 August 2019Source: Current Biology, Volume 29, Issue 15Author(s): Geert Kops
  • How to bring back our planet’s forests
    • Abstract: Publication date: 5 August 2019Source: Current Biology, Volume 29, Issue 15Author(s): Michael GrossSummaryAs an increasing number of protesters are keen to remind us, time is running out to avert a global climate catastrophe. Our globalised civilisation has to change direction in a whole range of aspects, but one of the easiest and most cost-efficient contributions to damage limitation is to plant many billions of trees. Reforestation efforts have already begun, but some have also been misguided. Michael Gross reports.
  • A New Enantiornithine Bird with Unusual Pedal Proportions Found in Amber
    • Abstract: Publication date: 5 August 2019Source: Current Biology, Volume 29, Issue 15Author(s): Lida Xing, Jingmai K. O’Connor, Luis M. Chiappe, Ryan C. McKellar, Nathan Carroll, Han Hu, Ming Bai, Fumin Lei
  • Genetic Depletion of Class I Odorant Receptors Impacts Perception of
           Carboxylic Acids
    • Abstract: Publication date: Available online 1 August 2019Source: Current BiologyAuthor(s): Annika Cichy, Ami Shah, Adam Dewan, Sarah Kaye, Thomas BozzaSummaryThe mammalian main olfactory pathway detects myriad volatile chemicals using>1,000 odorant receptor (OR) genes, which are organized into two phylogenetically distinct classes (class I and class II). An important question is how these evolutionarily conserved classes contribute to odor perception. Here, we report functional inactivation of a large number of class I ORs in mice via identification and deletion of a local cis-acting enhancer in the class I gene cluster. This manipulation reduced expression of half of the 131 intact class I genes. The resulting class I-depleted mice exhibited a significant reduction in the number of glomeruli responding to carboxylic acids—chemicals associated with microbial action and body odors. These mice also exhibit a change in odor perception marked by a selective loss of behavioral aversion to these compounds. Together, our data demonstrate that class I ORs play a critical role in representing a class of biologically relevant chemosignals.
  • Neuronal Correlates of Spatial Working Memory in the Endbrain of Crows
    • Abstract: Publication date: Available online 1 August 2019Source: Current BiologyAuthor(s): Paul Rinnert, Maximilian E. Kirschhock, Andreas NiederSummaryBirds are renowned for their excellent spatial cognition. Corvid songbirds, in particular, rely on explicit representation of spatial cues in memory when caching food and retrieving caches for later consumption. However, the neuronal correlates of flexible spatial memory abilities are largely unknown in birds. We therefore trained carrion crows (Corvus corone) on a spatial delayed-response task in which they had to maintain the variable location of a visual item for a few seconds in working memory. After the crows performed this task with high precision, we recorded single-cell activity from the associative endbrain area Nidopallium caudolaterale (NCL) in the behaving crows. A large fraction of NCL neurons were tuned to individual preferred locations and selectively maintained the spatial location of items in working memory. A comparison of firing rates with reaction times suggested that the majority of delay-selective neurons represented stored location information rather than motor preparation. Almost 30% of all recorded neurons were tuned during both visual presentation and memory delay, and their spatial tuning was significantly correlated. The population of recorded neurons stably maintained spatial information over the course of the working memory period. Importantly, the neural responses of spatially tuned neurons were relevant for the crows’ choices and allowed a statistical classifier to predict the subsequently chosen target location in free-choice trials. Our findings demonstrate the pivotal role of the avian NCL in spatial working memory that is reminiscent of the function of the convergently evolved primate prefrontal cortex in spatial working memory.Graphical Graphical abstract for this article
  • Synaptic-like Vesicles Facilitate Pioneer Axon Invasion
    • Abstract: Publication date: Available online 1 August 2019Source: Current BiologyAuthor(s): Evan L. Nichols, Cody J. SmithSummarySynaptic vesicles are indispensable for neuronal communication in mature circuits. Synaptic vesicle biogenesis must be concurrent with axon navigation for synaptogenesis, but whether synaptic vesicles are functionally employed in circuit formation before synaptogenesis is poorly understood. Here, we use time-lapse imaging and transgenesis in zebrafish to visualize the role of synaptic-like vesicles in navigation of dorsal root ganglia pioneer axons. We identify that synaptic-like vesicles accumulate in the central growth cone as the pioneer axon breaches the spinal boundary at the dorsal root entry zone. Inhibition of vesicle release with cell-specific tetanus toxin expression results in pioneer axon pathfinding defects and altered spinal entry. We further show that the matrix metalloproteinase (MMP) mmp14a is required in pioneer axons to navigate across the boundary of the spinal cord and, with super-resolution microscopy, is positioned with synaptic vesicles at the boundary. Manipulations of concurrent actin reorganization reveal that actin remodeling drives vesicle release and subsequent MMP activity. Together, these data point to an indispensable role for synaptic-like vesicles at specific points in axon navigation as regulators of growth cone microenvironment.
  • Environmental Barriers Disrupt Grid-like Representations in Humans during
    • Abstract: Publication date: Available online 1 August 2019Source: Current BiologyAuthor(s): Qiliang He, Thackery I. BrownSummaryEnvironmental barriers fundamentally shape our behavior and conceptualization of space [1, 2, 3, 4, 5]. Evidence from rodents suggests that, in contrast to an open-field environment, where grid cells exhibit firing patterns with a 6-fold rotational symmetry [5, 6], barriers within the field abolish the 6-fold symmetry and fragment the grid firing fields into compartmentalized repeating “submaps” [5]. These results suggest that barriers may exert their influence on the cognitive map through organization of the metric representation of space provided by entorhinal neurons. We directly tested this hypothesis in humans, combining functional MRI with a virtual navigation paradigm in which we manipulated the local barrier structure. When participants performed a fixed-route foraging task in an open field, the functional MRI signal in right entorhinal cortex exhibited a 6-fold periodic modulation by movement direction associated with conjunctive grid cell firing [7]. However, when environments were compartmentalized by barriers, the grid-like 6-fold spatial metric was abolished. Instead, a 4-fold modulation of the entorhinal signal was observed, consistent with a vectorized organization of spatial metrics predicted by rodent models of navigation [5]. Collectively, these results provide mechanistic insight into why barriers compartmentalize our cognitive map, indicating that boundaries exert a powerful influence on the way environments are represented in human entorhinal cortex. Given that our daily environments are rarely wide open and are often segmented by barriers (e.g., the buildings of our home city), our findings have implications for applying models of cognitive mapping based on grid-like metrics [8] to naturalistic circumstances.
  • The Embryos of Turtles Can Influence Their Own Sexual Destinies
    • Abstract: Publication date: Available online 1 August 2019Source: Current BiologyAuthor(s): Yin-Zi Ye, Liang Ma, Bao-Jun Sun, Teng Li, Yang Wang, Richard Shine, Wei-Guo DuSummarySessile organisms with thermally sensitive developmental trajectories are at high risk from climate change. For example, oviparous reptiles with temperature-dependent sex determination (TSD) may experience strong (potentially disastrous) shifts in offspring sex ratio if reproducing females are unable to predict incubation conditions at the time of oviposition. How then have TSD reptile taxa persisted over previous periods of extreme climatic conditions' An ability of embryos to move within the egg to select optimal thermal regimes could buffer ambient extremes, but the feasibility of behavioral thermoregulation by embryos has come under strong challenge. To test this idea, we measured thermal gradients within eggs in semi-natural nests of a freshwater turtle species with TSD, manipulated embryonic thermoregulatory ability, and modeled the effects of embryonic thermoregulation on offspring sex ratios. Behavioral thermoregulation by embryos accelerated development and influenced offspring sex ratio, expanding the range of ambient conditions under which nests produce equal numbers of male and female offspring. Model projections suggest that sex ratio shifts induced by global warming will be buffered by the ability of embryos to influence their sexual destiny via behavioral thermoregulation.
  • Germ Granules Govern Small RNA Inheritance
    • Abstract: Publication date: Available online 1 August 2019Source: Current BiologyAuthor(s): Itamar Lev, Itai Antoine Toker, Yael Mor, Anat Nitzan, Guy Weintraub, Olga Antonova, Ornit Bhonkar, Itay Ben Shushan, Uri Seroussi, Julie M. Claycomb, Sarit Anava, Hila Gingold, Ronen Zaidel-Bar, Oded RechaviSummaryIn C. elegans nematodes, components of liquid-like germ granules were shown to be required for transgenerational small RNA inheritance. Surprisingly, we show here that mutants with defective germ granules can nevertheless inherit potent small RNA-based silencing responses, but some of the mutants lose this ability after many generations of homozygosity. Animals mutated in pptr-1, which is required for stabilization of P granules in the early embryo, display extraordinarily strong heritable RNAi responses, lasting for tens of generations. Intriguingly, the RNAi capacity of descendants derived from mutants defective in the core germ granule proteins MEG-3 and MEG-4 is determined by the genotype of the ancestors and changes transgenerationally. Further, whether the meg-3/4 mutant alleles were present in the paternal or maternal lineages leads to different transgenerational consequences. Small RNA inheritance, rather than maternal contribution of the germ granules themselves, mediates the transgenerational defects in RNAi of meg-3/4 mutants and their progeny. Accordingly, germ granule defects lead to heritable genome-wide mis-expression of endogenous small RNAs. Upon disruption of germ granules, hrde-1 mutants can inherit RNAi, although HRDE-1 was previously thought to be absolutely required for RNAi inheritance. We propose that germ granules sort and shape the RNA pool, and that small RNA inheritance maintains this activity for multiple generations.Graphical Graphical abstract for this article
  • A KNOX-Cytokinin Regulatory Module Predates the Origin of Indeterminate
           Vascular Plants
    • Abstract: Publication date: Available online 1 August 2019Source: Current BiologyAuthor(s): Yoan Coudert, Ondřej Novák, C. Jill HarrisonSummaryThe diverse forms of today’s dominant vascular plant flora are generated by the sustained proliferative activity of sporophyte meristems at plants’ shoot and root tips, a trait known as indeterminacy [1]. Bryophyte sister lineages to the vascular plants lack such indeterminate meristems and have an overall sporophyte form comprising a single small axis that ceases growth in the formation of a reproductive sporangium [1]. Genetic mechanisms regulating indeterminacy are well characterized in flowering plants, involving a feedback loop between class I KNOX genes and cytokinin [2, 3], and class I KNOX expression is a conserved feature of vascular plant meristems [4]. The transition from determinate growth to indeterminacy during evolution was a pre-requisite to vascular plant diversification, but mechanisms enabling the innovation of indeterminacy are unknown [5]. Here, we show that class I KNOX gene activity is necessary and sufficient for axis extension from an intercalary region of determinate moss shoots. As in Arabidopsis, class I KNOX activity can promote cytokinin biosynthesis by an ISOPENTENYL TRANSFERASE gene, PpIPT3. PpIPT3 promotes axis extension, and PpIPT3 and exogenously applied cytokinin can partially compensate for loss of class I KNOX function. By outgroup comparison, the results suggest that a pre-existing KNOX-cytokinin regulatory module was recruited into vascular plant shoot meristems during evolution to promote indeterminacy, thereby enabling the radiation of vascular plant shoot forms.Graphical Graphical abstract for this article
  • Cadherin-Mediated Cell Coupling Coordinates Chemokine Sensing across
           Collectively Migrating Cells
    • Abstract: Publication date: Available online 1 August 2019Source: Current BiologyAuthor(s): Tugba Colak-Champollion, Ling Lan, Alisha R. Jadhav, Naoya Yamaguchi, Gayatri Venkiteswaran, Heta Patel, Michael Cammer, Martin Meier-Schellersheim, Holger KnautSummaryThe directed migration of cells sculpts the embryo, contributes to homeostasis in the adult, and, when dysregulated, underlies many diseases [1, 2]. During these processes, cells move singly or as a collective. In both cases, they follow guidance cues, which direct them to their destination [3, 4, 5, 6]. In contrast to single cells, collectively migrating cells need to coordinate with their neighbors to move together in the same direction. Recent studies suggest that leader cells in the front sense the guidance cue, relay the directional information to the follower cells in the back, and can pull the follower cells along [7, 8, 9, 10, 11, 12, 13, 14, 15, 16, 17, 18, 19]. In this manner, leader cells steer the collective and set the collective’s overall speed. However, whether follower cells also participate in steering and speed setting of the collective is largely unclear. Using chimeras, we analyzed the role of leader and follower cells in the collectively migrating zebrafish posterior lateral line primordium. This tissue expresses the chemokine receptor Cxcr4 and is guided by the chemokine Cxcl12a [20, 21, 22, 23]. We find that leader and follower cells need to sense the attractant Cxcl12a for efficient migration, are coupled to each other through cadherins, and require coupling to pull Cxcl12a-insensitive cells along. Analysis of cell dynamics in chimeric and protein-depleted primordia shows that Cxcl12a-sensing and cadherin-mediated adhesion contribute jointly to direct migration at both single-cell and tissue levels. These results suggest that all cells in the primordium need to sense the attractant and adhere to each other to coordinate their movements and migrate with robust directionality.Graphical Graphical abstract for this article
  • Cerebellar Prediction of the Dynamic Sensory Consequences of Gravity
    • Abstract: Publication date: Available online 1 August 2019Source: Current BiologyAuthor(s): Isabelle Mackrous, Jerome Carriot, Mohsen Jamali, Kathleen E. CullenSummaryAs we go about our everyday activities, our brain computes accurate estimates of both our motion relative to the world and our orientation relative to gravity. However, how the brain then accounts for gravity as we actively move and interact with our environment is not yet known. Here, we provide evidence that, although during passive movements, individual cerebellar output neurons encode representations of head motion and orientation relative to gravity, these gravity-driven responses are cancelled when head movement is a consequence of voluntary generated movement. In contrast, the gravity-driven responses of primary otolith and semicircular canal afferents remain intact during both active and passive self-motion, indicating the attenuated responses of central neurons are not inherited from afferent inputs. Taken together, our results are consistent with the view that the cerebellum builds a dynamic prediction (e.g., internal model) of the sensory consequences of gravity during active self-motion, which in turn enables the preferential encoding of unexpected motion to ensure postural and perceptual stability.Graphical Graphical abstract for this article
  • New Caledonian Crows Behave Optimistically after Using Tools
    • Abstract: Publication date: Available online 1 August 2019Source: Current BiologyAuthor(s): Dakota E. McCoy, Martina Schiestl, Patrick Neilands, Rebecca Hassall, Russell D. Gray, Alex H. TaylorSummaryAre complex, species-specific behaviors in animals reinforced by material reward alone or do they also induce positive emotions' Many adaptive human behaviors are intrinsically motivated: they not only improve our material outcomes, but improve our affect as well [1, 2, 3, 4, 5, 6, 7, 8]. Work to date on animal optimism, as an indicator of positive affect, has generally focused on how animals react to change in their circumstances, such as when their environment is enriched [9, 10, 11, 12, 13, 14] or they are manipulated by humans [15, 16, 17, 18, 19, 20, 21, 22, 23], rather than whether complex actions improve emotional state. Here, we show that wild New Caledonian crows are optimistic after tool use, a complex, species-specific behavior. We further demonstrate that this finding cannot be explained by the crows needing to put more effort into gaining food. Our findings therefore raise the possibility that intrinsic motivation (enjoyment) may be a fundamental proximate cause in the evolution of tool use and other complex behaviors.Video
  • Lifetime Fitness Costs of Inbreeding and Being Inbred in a Critically
           Endangered Bird
    • Abstract: Publication date: Available online 1 August 2019Source: Current BiologyAuthor(s): Katherine A. Harrisson, Michael J.L. Magrath, Jian D.L. Yen, Alexandra Pavlova, Neil Murray, Bruce Quin, Peter Menkhorst, Kimberly A. Miller, Karina Cartwright, Paul SunnucksSummaryReduced fitness as a result of inbreeding is a major threat facing many species of conservation concern [1, 2, 3, 4]. However, few case studies for assessing the magnitude of inbreeding depression in the wild means that its relative importance as a risk factor for population persistence remains under-appreciated [5]. The increasing availability and affordability of genomic technologies provide new opportunities to address knowledge gaps around the magnitude and manifestation of inbreeding depression in wild populations [6, 7, 8, 9, 10, 11, 12]. Here, we combine over three decades of individual lifetime reproductive data and genomic data to estimate the relative lifetime and short-term fitness costs of both being inbred and engaging in inbreeding in the last wild population (
  • Adaptation of Inhibition Mediates Retinal Sensitization
    • Abstract: Publication date: Available online 1 August 2019Source: Current BiologyAuthor(s): David B. Kastner, Yusuf Ozuysal, Georgia Panagiotakos, Stephen A. BaccusSummaryIn response to a changing sensory environment, sensory systems adjust their neural code for a number of purposes, including an enhanced sensitivity for novel stimuli, prediction of sensory features, and the maintenance of sensitivity. Retinal sensitization is a form of short-term plasticity that elevates local sensitivity following strong, local, visual stimulation and has been shown to create a prediction of the presence of a nearby localized object. The neural mechanism that generates this elevation in sensitivity remains unknown. Using simultaneous intracellular and multielectrode recording in the salamander retina, we show that a decrease in tonic amacrine transmission is necessary for and is correlated spatially and temporally with ganglion cell sensitization. Furthermore, introducing a decrease in amacrine transmission is sufficient to sensitize nearby ganglion cells. A computational model accounting for adaptive dynamics and nonlinear pathways confirms a decrease in steady inhibitory transmission can cause sensitization. Adaptation of inhibition enhances the sensitivity to the sensory feature conveyed by an inhibitory pathway, creating a prediction of future input.
  • Bats Actively Use Leaves as Specular Reflectors to Detect Acoustically
           Camouflaged Prey
    • Abstract: Publication date: Available online 1 August 2019Source: Current BiologyAuthor(s): Inga Geipel, Jan Steckel, Marco Tschapka, Dieter Vanderelst, Hans-Ulrich Schnitzler, Elisabeth K.V. Kalko, Herbert Peremans, Ralph SimonSummaryFiltering relevant signals from noisy sensory input is a crucial challenge for animals [1, 2]. Many bats are acoustic specialists relying on sound to find prey. They discern salient acoustic signals from irrelevant background masking noise. It has long been considered a sensory impossibility for bats to use solely echolocation for the detection of silent and motionless prey resting directly on foliage due to the masking effects of background echoes [3, 4]. Some bats, however, do successfully perform this seemingly impossible task [5], raising the question—what underlying acoustic and behavioral mechanisms do bats use to solve this conundrum' To address this question, we used biomimetic sonar to record high-resolution measurements of echoes from insects resting on leaves. Based on our echo recordings, we predicted optimal approach angles from which masking echoes can best be avoided. In behavioral experiments, we put these predictions to test. We recorded the prey approach behavior of wild bats in a flight cage equipped with an ultrasonic microphone synchronized with two high-speed cameras for 3D flightpath reconstructions. Bats approached prey from our predicted optimal oblique angles, using the leaf as a specular reflector to uncover previously acoustically hidden prey. Our findings disclose key behavioral and acoustic mechanisms enabling the detection of prey echoes that background clutter would otherwise mask. This work adds to the fundamental understanding of how bat echolocation strategies can override acoustic camouflage by silent, motionless prey, thus providing new insights into the evolutionary arms race between predators and their prey.
  • Natural Variation in TBP-ASSOCIATED FACTOR 4b Controls Meiotic Crossover
           and Germline Transcription in Arabidopsis
    • Abstract: Publication date: Available online 1 August 2019Source: Current BiologyAuthor(s): Emma J. Lawrence, Hongbo Gao, Andrew J. Tock, Christophe Lambing, Alexander R. Blackwell, Xiaoqi Feng, Ian R. HendersonSummaryMeiotic crossover frequency varies within genomes, which influences genetic diversity and adaptation. In turn, genetic variation within populations can act to modify crossover frequency in cis and trans. To identify genetic variation that controls meiotic crossover frequency, we screened Arabidopsis accessions using fluorescent recombination reporters. We mapped a genetic modifier of crossover frequency in Col × Bur populations of Arabidopsis to a premature stop codon within TBP-ASSOCIATED FACTOR 4b (TAF4b), which encodes a subunit of the RNA polymerase II general transcription factor TFIID. The Arabidopsis taf4b mutation is a rare variant found in the British Isles, originating in South-West Ireland. Using genetics, genomics, and immunocytology, we demonstrate a genome-wide decrease in taf4b crossovers, with strongest reduction in the sub-telomeric regions. Using RNA sequencing (RNA-seq) from purified meiocytes, we show that TAF4b expression is meiocyte enriched, whereas its paralog TAF4 is broadly expressed. Consistent with the role of TFIID in promoting gene expression, RNA-seq of wild-type and taf4b meiocytes identified widespread transcriptional changes, including in genes that regulate the meiotic cell cycle and recombination. Therefore, TAF4b duplication is associated with acquisition of meiocyte-specific expression and promotion of germline transcription, which act directly or indirectly to elevate crossovers. This identifies a novel mode of meiotic recombination control via a general transcription factor.
  • Dissociation between Postrhinal Cortex and Downstream Parahippocampal
           Regions in the Representation of Egocentric Boundaries
    • Abstract: Publication date: Available online 1 August 2019Source: Current BiologyAuthor(s): Xenia Gofman, Gilad Tocker, Shahaf Weiss, Charlotte N. Boccara, Li Lu, May-Britt Moser, Edvard I. Moser, Genela Morris, Dori DerdikmanSummaryNavigation requires the integration of many sensory inputs to form a multi-modal cognitive map of the environment, which is believed to be implemented in the hippocampal region by spatially tuned cells [1, 2, 3, 4, 5, 6, 7, 8, 9, 10]. These cells encode various aspects of the environment in a world-based (allocentric) reference frame. Although the cognitive map is represented in allocentric coordinates, the environment is sensed through diverse sensory organs, mostly situated in the animal’s head, and therefore represented in sensory and parietal cortices in head-centered egocentric coordinates. Yet it is not clear how and where the brain transforms these head-centered egocentric representations to map-like allocentric representations computed in the hippocampal region. Theoretical modeling has predicted a role for both egocentric and head direction (HD) information in performing an egocentric-allocentric transformation [11, 12, 13, 14, 15]. Here, we recorded new data and also used data from a previous study [16]. Adapting a generalized linear model (GLM) classification [17]; we show that the postrhinal cortex (POR) contains a population of pure egocentric boundary cells (EBCs), in contrast with the conjunctive EBCs × HD cells, which we found downstream mostly in the parasubiculum (PaS) and in the medial entorhinal cortex (MEC). Our finding corroborates the idea of a brain network performing an egocentric to allocentric transformation by HD cells. This is a fundamental building block in the formation of the brain’s internal cognitive map.
  • Multiple Reinventions of Mating-type Switching during Budding Yeast
    • Abstract: Publication date: Available online 25 July 2019Source: Current BiologyAuthor(s): Tadeusz Krassowski, Jacek Kominek, Xing-Xing Shen, Dana A. Opulente, Xiaofan Zhou, Antonis Rokas, Chris Todd Hittinger, Kenneth H. WolfeSummaryCell type in budding yeasts is determined by the genotype at the mating-type (MAT) locus, but yeast species differ widely in their mating compatibility systems and life cycles. Among sexual yeasts, heterothallic species are those in which haploid strains fall into two distinct and stable mating types (MATa and MATα), whereas homothallic species are those that can switch mating types or that appear not to have distinct mating types [1, 2]. The evolutionary history of these mating compatibility systems is uncertain, particularly regarding the number and direction of transitions between homothallism and heterothallism, and regarding whether the process of mating-type switching had a single origin [3, 4, 5]. Here, we inferred the mating compatibility systems of 332 budding yeast species from their genome sequences. By reference to a robust phylogenomic tree [6], we detected evolutionary transitions between heterothallism and homothallism, and among different forms of homothallism. We find that mating-type switching has arisen independently at least 11 times during yeast evolution and that transitions from heterothallism to homothallism greatly outnumber transitions in the opposite direction (31 versus 3). Although the 3-locus MAT-HML-HMR mechanism of mating-type switching as seen in Saccharomyces cerevisiae had a single evolutionary origin in budding yeasts, simpler “flip/flop” mechanisms of switching evolved separately in at least 10 other groups of yeasts. These results point to the adaptive value of homothallism and mating-type switching to unicellular fungi.
  • Short- and Long-Term Effects of UVA on Arabidopsis Are Mediated by a Novel
           cGMP Phosphodiesterase
    • Abstract: Publication date: Available online 25 July 2019Source: Current BiologyAuthor(s): Jean-Charles Isner, Vlad-Aris Olteanu, Alexander J. Hetherington, Aude Coupel-Ledru, Peng Sun, Ashley J. Pridgeon, Glyndyr S. Jones, Matthew Oates, Tom A. Williams, Frans J.M. Maathuis, Richard Kift, Ann R. Webb, Julian Gough, Keara A. Franklin, Alistair M. HetheringtonSummaryAlthough UVA radiation (315–400 nm) represents 95% of the UV radiation reaching the earth’s surface, surprisingly little is known about its effects on plants [1]. We show that in Arabidopsis, short-term exposure to UVA inhibits the opening of stomata, and this requires a reduction in the cytosolic level of cGMP. This process is independent of UVR8, the UVB receptor. A cGMP-activated phosphodiesterase (AtCN-PDE1) was responsible for the UVA-induced decrease in cGMP in Arabidopsis. AtCN-PDE1-like proteins form a clade within the large HD-domain/PDEase-like protein superfamily, but no eukaryotic members of this subfamily have been functionally characterized. These genes have been lost from the genomes of metazoans but are otherwise conserved as single-copy genes across the tree of life. In longer-term experiments, UVA radiation increased growth and decreased water-use efficiency. These experiments revealed that PDE1 is also a negative regulator of growth. As the PDE1 gene is ancient and not represented in animal lineages, it is likely that at least one element of cGMP signaling in plants has evolved differently to the system present in metazoans.
  • Ancient Genomes Reveal Yamnaya-Related Ancestry and a Potential Source of
           Indo-European Speakers in Iron Age Tianshan
    • Abstract: Publication date: Available online 25 July 2019Source: Current BiologyAuthor(s): Chao Ning, Chuan-Chao Wang, Shizhu Gao, Yang Yang, Xue Zhang, Xiyan Wu, Fan Zhang, Zhongzhi Nie, Yunpeng Tang, Martine Robbeets, Jian Ma, Johannes Krause, Yinqiu CuiSummaryRecent studies of early Bronze Age human genomes revealed a massive population expansion by individuals-related to the Yamnaya culture, from the Pontic Caspian steppe into Western and Eastern Eurasia, likely accompanied by the spread of Indo-European languages [1, 2, 3, 4, 5]. The south eastern extent of this migration is currently not known. Modern-day human populations from the Xinjiang region in northwestern China show a complex population history, with genetic links to both Eastern and Western Eurasia [6, 7, 8, 9, 10]. However, due to the lack of ancient genomic data, it remains unclear which source populations contributed to the Xinjiang population and what was the timing and the number of admixture events. Here, we report the first genome-wide data of 10 ancient individuals from northeastern Xinjiang. They are dated to around 2,200 years ago and were found at the Iron Age Shirenzigou site. We find them to be already genetically admixed between Eastern and Western Eurasians. We also find that the majority of the East Eurasian ancestry in the Shirenzigou individuals is-related to northeastern Asian populations, while the West Eurasian ancestry is best presented by ∼20% to 80% Yamnaya-like ancestry. Our data thus suggest a Western Eurasian steppe origin for at least part of the ancient Xinjiang population. Our findings furthermore support a Yamnaya-related origin for the now extinct Tocharian languages in the Tarim Basin, in southern Xinjiang.
  • Structure of the Human Core Centromeric Nucleosome Complex
    • Abstract: Publication date: Available online 25 July 2019Source: Current BiologyAuthor(s): Praveen Kumar Allu, Jennine M. Dawicki-McKenna, Trevor Van Eeuwen, Moriya Slavin, Merav Braitbard, Chen Xu, Nir Kalisman, Kenji Murakami, Ben E. BlackSummaryCentromeric nucleosomes are at the interface of the chromosome and the kinetochore that connects to spindle microtubules in mitosis. The core centromeric nucleosome complex (CCNC) harbors the histone H3 variant, CENP-A, and its binding proteins, CENP-C (through its central domain; CD) and CENP-N (through its N-terminal domain; NT). CENP-C can engage nucleosomes through two domains: the CD and the CENP-C motif (CM). CENP-CCD is part of the CCNC by virtue of its high specificity for CENP-A nucleosomes and ability to stabilize CENP-A at the centromere. CENP-CCM is thought to engage a neighboring nucleosome, either one containing conventional H3 or CENP-A, and a crystal structure of a nucleosome complex containing two copies of CENP-CCM was reported. Recent structures containing a single copy of CENP-NNT bound to the CENP-A nucleosome in the absence of CENP-C were reported. Here, we find that one copy of CENP-N is lost for every two copies of CENP-C on centromeric chromatin just prior to kinetochore formation. We present the structures of symmetric and asymmetric forms of the CCNC that vary in CENP-N stoichiometry. Our structures explain how the central domain of CENP-C achieves its high specificity for CENP-A nucleosomes and how CENP-C and CENP-N sandwich the histone H4 tail. The natural centromeric DNA path in our structures corresponds to symmetric surfaces for CCNC assembly, deviating from what is observed in prior structures using artificial sequences. At mitosis, we propose that CCNC asymmetry accommodates its asymmetric connections at the chromosome/kinetochore interface.Video Graphical Graphical abstract for this article
  • Circadian Regulation of Cochlear Sensitivity to Noise by Circulating
    • Abstract: Publication date: Available online 25 July 2019Source: Current BiologyAuthor(s): Christopher R. Cederroth, Jung-sub Park, Vasiliki Basinou, Benjamin D. Weger, Evangelia Tserga, Heela Sarlus, Anna K. Magnusson, Nadir Kadri, Frédéric Gachon, Barbara CanlonSummaryThe cochlea possesses a robust circadian clock machinery that regulates auditory function. How the cochlear clock is influenced by the circadian system remains unknown. Here, we show that cochlear rhythms are system driven and require local Bmal1 as well as central input from the suprachiasmatic nuclei (SCN). SCN ablations disrupted the circadian expression of the core clock genes in the cochlea. Because the circadian secretion of glucocorticoids (GCs) is controlled by the SCN and GCs are known to modulate auditory function, we assessed their influence on circadian gene expression. Removal of circulating GCs by adrenalectomy (ADX) did not have a major impact on core clock gene expression in the cochlea. Rather it abolished the transcription of clock-controlled genes involved in inflammation. ADX abolished the known differential auditory sensitivity to day and night noise trauma and prevented the induction of GABA-ergic and glutamate receptors mRNA transcripts. However, these improvements were unrelated to changes at the synaptic level, suggesting other cochlear functions may be involved. Due to this circadian regulation of noise sensitivity by GCs, we evaluated the actions of the synthetic glucocorticoid dexamethasone (DEX) at different times of the day. DEX was effective in protecting from acute noise trauma only when administered during daytime, when circulating glucocorticoids are low, indicating that chronopharmacological approaches are important for obtaining optimal treatment strategies for hearing loss. GCs appear as a major regulator of the differential sensitivity to day or night noise trauma, a mechanism likely involving the circadian control of inflammatory responses.Graphical Graphical abstract for this article
  • Monovision and the Misperception of Motion
    • Abstract: Publication date: Available online 25 July 2019Source: Current BiologyAuthor(s): Johannes Burge, Victor Rodriguez-Lopez, Carlos DorronsoroSummaryMonovision is a common prescription lens correction for presbyopia [1]. Each eye is corrected for a different distance, causing one image to be blurrier than the other. Millions of people have monovision corrections, but little is known about how interocular blur differences affect motion perception. Here, we report that blur differences cause a previously unknown motion illusion that makes people dramatically misperceive the distance and three-dimensional direction of moving objects. The effect occurs because the blurry and sharp images are processed at different speeds. For moving objects, the mismatch in processing speed causes a neural disparity, which results in the misperceptions. A variant of a 100-year-old stereo-motion phenomenon called the Pulfrich effect [2], the illusion poses an apparent paradox: blur reduces contrast, and contrast reductions are known to cause neural processing delays [3, 4, 5, 6], but our results indicate that blurry images are processed milliseconds more quickly. We resolve the paradox with known properties of the early visual system, show that the misperceptions can be severe enough to impact public safety, and demonstrate that the misperceptions can be eliminated with novel combinations of non-invasive ophthalmic interventions. The fact that substantial perceptual errors are caused by millisecond differences in processing speed highlights the exquisite temporal calibration required for accurate perceptual estimation. The motion illusion—the reverse Pulfrich effect—and the paradigm we use to measure it should help reveal how optical and image properties impact temporal processing, an important but understudied issue in vision and visual neuroscience.Graphical Graphical abstract for this article
  • A Secreted Ig-Domain Protein Required in Both Astrocytes and Neurons for
           Regulation of Drosophila Night Sleep
    • Abstract: Publication date: Available online 25 July 2019Source: Current BiologyAuthor(s): Sukanya Sengupta, Lauren B. Crowe, Samantha You, Mary A. Roberts, F. Rob JacksonSummaryEndogenous rhythmic behaviors are evolutionarily conserved and essential for life. In mammalian and invertebrate models, well-characterized neuronal circuits and evolutionarily conserved mechanisms regulate circadian behavior and sleep [1, 2, 3, 4]. In Drosophila, neuronal populations located in multiple brain regions mediate arousal, sleep drive, and homeostasis (reviewed in [3, 5, 6, 7]). Similar to mammals [8], there is also evidence that fly glial cells modulate the neuronal circuits controlling rhythmic behaviors, including sleep [1]. Here, we describe a novel gene (CG14141; aka Nkt) that is required for normal sleep. NKT is a 162-amino-acid protein with a single IgC2 immunoglobulin (Ig) domain and a high-quality signal peptide [9], and we show evidence that it is secreted, similar to its C. elegans ortholog (OIG-4) [10]. We demonstrate that Nkt-null flies or those with selective knockdown in either neurons or glia have decreased and fragmented night sleep, indicative of a non-redundant requirement in both cell types. We show that Nkt is required in fly astrocytes and in a specific set of wake-promoting neurons—the mushroom body (MB) α’β’ cells that link sleep to memory consolidation [11]. Importantly, Nkt gene expression is required in the adult nervous system for normal sleep, consistent with a physiological rather than developmental function for the Ig-domain protein.
  • CB1 Receptors in the Anterior Piriform Cortex Control Odor Preference
    • Abstract: Publication date: Available online 18 July 2019Source: Current BiologyAuthor(s): Geoffrey Terral, Arnau Busquets-Garcia, Marjorie Varilh, Svein Achicallende, Astrid Cannich, Luigi Bellocchio, Itziar Bonilla-Del Río, Federico Massa, Nagore Puente, Edgar Soria-Gomez, Pedro Grandes, Guillaume Ferreira, Giovanni MarsicanoSummaryThe retrieval of odor-related memories shapes animal behavior. The anterior piriform cortex (aPC) is the largest part of the olfactory cortex, and it plays important roles in olfactory processing and memory. However, it is still unclear whether specific cellular mechanisms in the aPC control olfactory memory, depending on the appetitive or aversive nature of the stimuli involved. Cannabinoid-type 1 (CB1) receptors are present in the aPC (aPC-CB1), but their potential impact on olfactory memory was never explored. Here, we used a combination of behavioral, genetic, anatomical, and electrophysiological approaches to characterize the functions of aPC-CB1 receptors in the regulation of appetitive and aversive olfactory memory. Pharmacological blockade or genetic deletion of aPC-CB1 receptors specifically impaired the retrieval of conditioned odor preference (COP). Interestingly, expression of conditioned odor aversion (COA) was unaffected by local CB1 receptor blockade, indicating that the role of aPC endocannabinoid signaling is selective for retrieval of appetitive memory. Anatomical investigations revealed that CB1 receptors are highly expressed on aPC GABAergic interneurons, and ex vivo electrophysiological recordings showed that their pharmacological activation reduces miniature inhibitory post-synaptic currents (mIPSCs) onto aPC semilunar (SL), but not pyramidal principal neurons. COP retrieval, but not COA, was associated with a specific CB1-receptor-dependent decrease of mIPSCs in SL cells. Altogether, these data indicate that aPC-CB1 receptor-dependent mechanisms physiologically control the retrieval of olfactory memory, depending on odor valence and engaging modulation of local inhibitory transmission.
  • Causal Evidence for Expression of Perceptual Expectations in
           Category-Selective Extrastriate Regions
    • Abstract: Publication date: Available online 18 July 2019Source: Current BiologyAuthor(s): Marco Gandolfo, Paul Edward DowningSummaryExpectations about a visual event shape the way it is perceived [1, 2, 3, 4]. For example, expectations induced by valid cues signaling aspects of a visual target can improve judgments about that target, relative to invalid cues [5, 6]. Such expectation effects are thought to arise via pre-activation of a template in neural populations that represent the target [7, 8] in early sensory areas [9] or in higher-level regions. For example, category cues (“face” or “house”) modulate pre-target fMRI activity in associated category-selective brain regions [10, 11]. Further, a relationship is sometimes found between the strength of template activity and success in perceptual tasks on the target [12, 13, 14]. However, causal evidence linking pre-target activity with expectation effects is lacking. Here we provide such evidence, using fMRI-guided online transcranial magnetic stimulation (TMS). In two experiments, human volunteers made binary judgments about images of either a body or a scene. Before each target image, a verbal cue validly or invalidly indicated a property of the image, thus creating perceptual expectations about it. To disrupt these expectations, we stimulated category-selective visual brain regions (extrastriate body area, EBA; occipital place area, OPA) during the presentation of the cue. Stimulation ended before the target images appeared. We found a double dissociation: TMS to EBA during the cue period removed validity effects only in the body task, whereas stimulating OPA removed validity effects only in the scene task. Perceptual expectations are expressed by the selective activation of relevant populations within brain regions that encode the target.
  • Mating Suppresses Alarm Response in Zebrafish
    • Abstract: Publication date: Available online 18 July 2019Source: Current BiologyAuthor(s): Carmen Diaz-Verdugo, Gerald J. Sun, Caroline H. Fawcett, Peixin Zhu, Mark C. FishmanSummaryMating and flight from threats are innate behaviors that enhance species survival [1, 2]. Stimuli to these behaviors often are contemporaneous and conflicting [3, 4]. Both how such conflicts are resolved and where in the brain such decisions are made are poorly understood. For teleosts, olfactory stimuli are key elements of mating and threat responses [5, 6, 7]. For example, zebrafish manifest a stereotypical escape response when exposed to an alarm substance released from injured conspecific skin (“skin extract”) [8, 9]. We find that when mating, fish ignore this threatening stimulus. Water conditioned by the mating fish (“mating water”) suffices to suppress much of the alarm-response behavior. By 2-photon imaging of calcium transients [10], we mapped the regions of the brain responding to skin extract and to mating water. In the telencephalon, we found regions where the responses overlap, one region (medial Dp) to be predominantly activated by skin extract, and another, Vs, to be predominantly activated by mating water. When mating water and skin extract were applied simultaneously, the alarm-specific response was suppressed, while the mating-water-specific response was retained, corresponding to the dominance of mating over flight behavior. The choice made, for reproduction over escape, is opposite to that of mammals, presumably reflecting how the balance affects species survival.
  • m5C Methylation Guides Systemic Transport of Messenger RNA over
           Graft Junctions in Plants
    • Abstract: Publication date: Available online 18 July 2019Source: Current BiologyAuthor(s): Lei Yang, Valentina Perrera, Eleftheria Saplaoura, Federico Apelt, Mathieu Bahin, Amira Kramdi, Justyna Olas, Bernd Mueller-Roeber, Ewelina Sokolowska, Wenna Zhang, Runsheng Li, Nicolas Pitzalis, Manfred Heinlein, Shoudong Zhang, Auguste Genovesio, Vincent Colot, Friedrich KraglerSummaryIn plants, transcripts move to distant body parts to potentially act as systemic signals regulating development and growth. Thousands of messenger RNAs (mRNAs) are transported across graft junctions via the phloem to distinct plant parts. Little is known regarding features, structural motifs, and potential base modifications of transported transcripts and how these may affect their mobility. We identified Arabidopsis thaliana mRNAs harboring the modified base 5-methylcytosine (m5C) and found that these are significantly enriched in mRNAs previously described as mobile, moving over graft junctions to distinct plant parts. We confirm this finding with graft-mobile methylated mRNAs TRANSLATIONALLY CONTROLLED TUMOR PROTEIN 1 (TCTP1) and HEAT SHOCK COGNATE PROTEIN 70.1 (HSC70.1), whose mRNA transport is diminished in mutants deficient in m5C mRNA methylation. Together, our results point toward an essential role of cytosine methylation in systemic mRNA mobility in plants and that TCTP1 mRNA mobility is required for its signaling function.Graphical Graphical abstract for this article
  • Learning a Spatial Task by Trial and Error in Drosophila
    • Abstract: Publication date: Available online 18 July 2019Source: Current BiologyAuthor(s): Ulrich Stern, Hemant Srivastava, Hsueh-Ling Chen, Farhan Mohammad, Adam Claridge-Chang, Chung-Hui YangSummaryThe ability to use memory to return to specific locations for foraging is advantageous for survival. Although recent reports have demonstrated that the fruit flies Drosophila melanogaster are capable of visual cue-driven place learning and idiothetic path integration [1, 2, 3, 4], the depth and flexibility of Drosophila’s ability to solve spatial tasks and the underlying neural substrate and genetic basis have not been extensively explored. Here, we show that Drosophila can remember a reward-baited location through reinforcement learning and do so quickly and without requiring vision. After gaining genetic access to neurons (through 0273-GAL4) with properties reminiscent of the vertebrate medial forebrain bundle (MFB) and developing a high-throughput closed-loop stimulation system, we found that both sighted and blind flies can learn—by trial and error—to repeatedly return to an unmarked location (in a rectangularly shaped arena) where a brief stimulation of the 0273-GAL4 neurons was available for each visit. We found that optogenetic stimulation of these neurons enabled learning by employing both a cholinergic pathway that promoted self-stimulation and a dopaminergic pathway that likely promoted association of relevant cues with reward. Lastly, inhibiting activities of specific neurons time-locked with stimulation of 0273-GAL4 neurons showed that mushroom bodies (MB) and central complex (CX) both play a role in promoting learning of our task. Our work uncovered new depth in flies’ ability to learn a spatial task and established an assay with a level of throughput that permits a systematic genetic interrogation of flies’ ability to learn spatial tasks.
  • A Cellular Insulator against CLE45 Peptide Signaling
    • Abstract: Publication date: Available online 18 July 2019Source: Current BiologyAuthor(s): Alice S. Breda, Ora Hazak, Patrick Schultz, Pauline Anne, Moritz Graeff, Rüdiger Simon, Christian S. HardtkeSummaryPlants continuously elaborate their bodies through post-embryonic, reiterative organ formation by apical meristems [1]. Meristems harbor stem cells, which produce daughter cells that divide repeatedly before they differentiate. How transitions between stemness, proliferation, and differentiation are precisely coordinated is not well understood, but it is known that phytohormones as well as peptide signals play important roles [2, 3, 4, 5, 6, 7]. For example, in Arabidopsis thaliana root meristems, developing protophloem sieve elements (PPSEs) express the secreted CLAVATA3/EMBRYO SURROUNDING REGION-RELATED 45 (CLE45) peptide and its cognate receptor, the leucine-rich repeat receptor kinase (LRR-RK) BARELY ANY MERISTEM 3 (BAM3). Exogenous CLE45 application or transgenically increased CLE45 dosage impairs protophloem formation, suggesting autocrine inhibition of PPSE differentiation by CLE45 signaling. Since CLE45 and BAM3 are expressed throughout PPSE development, it remains unclear how this inhibition is eventually overcome. The OCTOPUS (OPS) gene is required for proper PPSE differentiation and therefore the formation of continuous protophloem strands. OPS dosage increase can mend the phenotype of other mutants that display protophloem development defects in association with CLE45-BAM3 hyperactivity [8, 9]. Here, we provide evidence that OPS protein promotes differentiation of developing PPSEs by dampening CLE45 perception. This markedly quantitative antagonism is likely mediated through direct physical interference of OPS with CLE45 signaling component interactions. Moreover, hyperactive OPS confers resistance to other CLE peptides, and ectopic OPS overexpression triggers premature differentiation throughout the root. Our results thus reveal a novel mechanism in PPSE transition toward differentiation, wherein OPS acts as an “insulator” to antagonize CLE45 signaling.
  • Cytoskeleton Dynamics Are Necessary for Early Events of Lateral Root
           Initiation in Arabidopsis
    • Abstract: Publication date: Available online 18 July 2019Source: Current BiologyAuthor(s): Amaya Vilches Barro, Dorothee Stöckle, Martha Thellmann, Paola Ruiz-Duarte, Lotte Bald, Marion Louveaux, Patrick von Born, Philipp Denninger, Tatsuaki Goh, Hidehiro Fukaki, Joop E.M. Vermeer, Alexis MaizelSummaryHow plant cells re-establish differential growth to initiate organs is poorly understood. Morphogenesis of lateral roots relies on the asymmetric cell division of initially symmetric founder cells. This division is preceded by the tightly controlled asymmetric radial expansion of these cells. The cellular mechanisms that license and ensure the coordination of these events are unknown. Here, we quantitatively analyze microtubule and F-actin dynamics during lateral root initiation. Using mutants and pharmacological and tissue-specific genetic perturbations, we show that dynamic reorganization of both microtubule and F-actin networks is necessary for the asymmetric expansion of the founder cells. This cytoskeleton remodeling intertwines with auxin signaling in the pericycle and endodermis in order for founder cells to acquire a basic polarity required for initiating lateral root development. Our results reveal the conservation of cell remodeling and polarization strategies between the Arabidopsis zygote and lateral root founder cells. We propose that coordinated, auxin-driven reorganization of the cytoskeleton licenses asymmetric cell growth and divisions during embryonic and post-embryonic organogenesis.
  • Scaling Principles of Distributed Circuits
    • Abstract: Publication date: Available online 18 July 2019Source: Current BiologyAuthor(s): Shyam Srinivasan, Charles F. StevensSummaryIdentifying shared quantitative features of a neural circuit across species is important for 3 reasons. Often expressed in the form of power laws and called scaling relationships [1, 2], they reveal organizational principles of circuits, make insights gleaned from model systems widely applicable, and explain circuit performance and function, e.g., visual circuits [3, 4]. The visual circuit is topographic [5, 6], wherein retinal neurons target and activate predictable spatial loci in primary visual cortex. The brain, however, contains many circuits, where neuronal targets and activity are unpredictable and distributed throughout the circuit, e.g., olfactory circuits, in which glomeruli (or mitral cells) in the olfactory bulb synapse with neurons distributed throughout the piriform cortex [7, 8, 9, 10]. It is unknown whether such circuits, which we term distributed circuits, are scalable. To determine whether distributed circuits scale, we obtained quantitative descriptions of the olfactory bulb and piriform cortex in six mammals using stereology techniques and light microscopy. Two conserved features provide evidence of scalability. First, the number of piriform neurons n and bulb glomeruli g scale as n∼g3/2. Second, the average number of synapses between a bulb glomerulus and piriform neuron is invariant at one. Using theory and modeling, we show that these two features preserve the discriminatory ability and precision of odor information across the olfactory circuit. As both abilities depend on circuit size, manipulating size provides evolution with a way to adapt a species to its niche without designing developmental programs de novo. These principles might apply to other distributed circuits like the hippocampus.
  • Visual-Olfactory Integration in the Human Disease Vector Mosquito
           Aedes aegypti
    • Abstract: Publication date: Available online 18 July 2019Source: Current BiologyAuthor(s): Clément Vinauger, Floris Van Breugel, Lauren T. Locke, Kennedy K.S. Tobin, Michael H. Dickinson, Adrienne L. Fairhall, Omar S. Akbari, Jeffrey A. RiffellSummaryMosquitoes rely on the integration of multiple sensory cues, including olfactory, visual, and thermal stimuli, to detect, identify, and locate their hosts [1, 2, 3, 4]. Although we increasingly know more about the role of chemosensory behaviors in mediating mosquito-host interactions [1], the role of visual cues is comparatively less studied [3], and how the combination of olfactory and visual information is integrated in the mosquito brain remains unknown. In the present study, we used a tethered-flight light-emitting diode (LED) arena, which allowed for quantitative control over the stimuli, and a control theoretic model to show that CO2 modulates mosquito steering responses toward vertical bars. To gain insight into the neural basis of this olfactory and visual coupling, we conducted two-photon microscopy experiments in a new GCaMP6s-expressing mosquito line. Imaging revealed that neuropil regions within the lobula exhibited strong responses to objects, such as a bar, but showed little response to a large-field motion. Approximately 20% of the lobula neuropil we imaged were modulated when CO2 preceded the presentation of a moving bar. By contrast, responses in the antennal (olfactory) lobe were not modulated by visual stimuli presented before or after an olfactory stimulus. Together, our results suggest that asymmetric coupling between these sensory systems provides enhanced steering responses to discrete objects.Graphical Graphical abstract for this article
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