Journal Cover Current Biology
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  • Non-canonical Phototransduction Mediates Synchronization of the Drosophila
           melanogaster Circadian Clock and Retinal Light Responses
    • Abstract: Publication date: Available online 17 May 2018
      Source:Current Biology
      Author(s): Maite Ogueta, Roger C. Hardie, Ralf Stanewsky
      The daily light-dark cycles represent a key signal for synchronizing circadian clocks. Both insects and mammals possess dedicated “circadian” photoreceptors but also utilize the visual system for clock resetting. In Drosophila, circadian clock resetting is achieved by the blue-light photoreceptor cryptochrome (CRY), which is expressed within subsets of the brain clock neurons. In addition, rhodopsin-expressing photoreceptor cells contribute to light synchronization. Light resets the molecular clock by CRY-dependent degradation of the clock protein Timeless (TIM), although in specific subsets of key circadian pacemaker neurons, including the small ventral lateral neurons (s-LNvs), TIM and Period (PER) oscillations can be synchronized by light independent of CRY and canonical visual Rhodopsin phototransduction. Here, we show that at least three of the seven Drosophila rhodopsins can utilize an alternative transduction mechanism involving the same α-subunit of the heterotrimeric G protein operating in canonical visual phototransduction (Gq). Surprisingly, in mutants lacking the canonical phospholipase C-β (PLC-β) encoded by the no receptor potential A (norpA) gene, we uncovered a novel transduction pathway using a different PLC-β encoded by the Plc21C gene. This novel pathway is important for behavioral clock resetting to semi-natural light-dark cycles and mediates light-dependent molecular synchronization within the s-LNv clock neurons. The same pathway appears to be responsible for norpA-independent light responses in the compound eye. We show that Rhodopsin 5 (Rh5) and Rh6, present in the R8 subset of retinal photoreceptor cells, drive both the long-term circadian and rapid light responses in the eye.
      Graphical abstract image Teaser Light synchronization of the Drosophila circadian clock relies on cryptochrome and rhodopsin photoreceptors. Ogueta et al. reveal that rhodopsin signaling to the clock involves non-canonical phototransduction, which synchronizes key circadian pacemaker neurons and behavior. In the eye, the same pathway can mediate ERG responses to brief light pulses.

      PubDate: 2018-05-18T08:30:43Z
       
  • The XMAP215 Ortholog Alp14 Promotes Microtubule Nucleation in Fission
           Yeast
    • Abstract: Publication date: Available online 17 May 2018
      Source:Current Biology
      Author(s): Ignacio Flor-Parra, Ana Belén Iglesias-Romero, Fred Chang
      The organization and number of microtubules (MTs) in a cell depend on the proper regulation of MT nucleation. Currently, the mechanism of nucleation is the most poorly understood aspect of MT dynamics. XMAP215/chTOG/Alp14/Stu2 proteins are MT polymerases that stimulate MT polymerization at MT plus ends by binding and releasing tubulin dimers. Although these proteins also localize to MT organizing centers and have nucleating activity in vitro, it is not yet clear whether these proteins participate in MT nucleation in vivo. Here, we demonstrate that in the fission yeast Schizosaccharomyces pombe, the XMAP215 ortholog Alp14 is critical for efficient MT nucleation in vivo. In multiple assays, loss of Alp14 function led to reduced nucleation rate and numbers of interphase MT bundles. Conversely, activation of Alp14 led to increased nucleation frequency. Alp14 associated with Mto1 and γ-tubulin complex components, and artificially targeting Alp14 to the γ-tubulin ring complexes (γ-TuRCs) stimulated nucleation. In imaging individual nucleation events, we found that Alp14 transiently associated with a γ-tubulin particle shortly before the appearance of a new MT. The transforming acidic coiled-coil (TACC) ortholog Alp7 mediated the localization of Alp14 at nucleation sites but not plus ends, and was required for efficient nucleation but not for MT polymerization. Our findings provide the strongest evidence to date that Alp14 serves as a critical MT nucleation factor in vivo. We suggest a model in which Alp14 associates with the γ-tubulin complex in an Alp7-dependent manner to facilitate the assembly or stabilization of the nascent MT.
      Teaser Microtubules are dynamic polymers that help to organize cellular contents and divide the cell. New microtubules arise by a process of nucleation, in which tubulin subunits are stitched together to begin forming a hollow tube. Flor-Parra et al. identify XMAP215/Alp14 as a nucleation factor that facilitates the assembly of the microtubule.

      PubDate: 2018-05-18T08:30:43Z
       
  • Developmental Upregulation of Ephrin-B1 Silences Sema3C/Neuropilin-1
           Signaling during Post-crossing Navigation of Corpus Callosum Axons
    • Abstract: Publication date: Available online 17 May 2018
      Source:Current Biology
      Author(s): Erik Mire, Mélanie Hocine, Elsa Bazellières, Thomas Jungas, Alice Davy, Sophie Chauvet, Fanny Mann
      The corpus callosum is the largest commissure in the brain, whose main function is to ensure communication between homotopic regions of the cerebral cortex. During fetal development, corpus callosum axons (CCAs) grow toward and across the brain midline and then away on the contralateral hemisphere to their targets. A particular feature of this circuit, which raises a key developmental question, is that the outgoing trajectory of post-crossing CCAs is mirror-symmetric with the incoming trajectory of pre-crossing axons. Here, we show that post-crossing CCAs switch off their response to axon guidance cues, among which the secreted Semaphorin-3C (Sema3C), that act as attractants for pre-crossing axons on their way to the midline. This change is concomitant with an upregulation of the surface protein Ephrin-B1, which acts in CCAs to inhibit Sema3C signaling via interaction with the Neuropilin-1 (Nrp1) receptor. This silencing activity is independent of Eph receptors and involves a N-glycosylation site (N-139) in the extracellular domain of Ephrin-B1. Together, our results reveal a molecular mechanism, involving interaction between the two unrelated guidance receptors Ephrin-B1 and Nrp1, that is used to control the navigation of post-crossing axons in the corpus callosum.
      Graphical abstract image Teaser Mire et al. discover a unique interaction between Ephrin-B1 and Nrp1 that turns off the axonal response to the Sema3C attractant. This molecular on/off switch allows callosal axons to move across mirror-symmetrical gradients of Sema3C on both sides of the brain midline.

      PubDate: 2018-05-18T08:30:43Z
       
  • Linear Self-Motion Cues Support the Spatial Distribution and Stability of
           Hippocampal Place Cells
    • Abstract: Publication date: Available online 17 May 2018
      Source:Current Biology
      Author(s): Ryan E. Harvey, Stephanie A. Rutan, Gabrielle R. Willey, Jennifer J. Siegel, Benjamin J. Clark, Ryan M. Yoder
      The vestibular system provides a crucial component of place-cell and head-direction cell activity [1–7]. Otolith signals are necessary for head-direction signal stability and associated behavior [8, 9], and the head-direction signal’s contribution to parahippocampal spatial representations [10–14] suggests that place cells may also require otolithic information. Here, we demonstrate that self-movement information from the otolith organs is necessary for the development of stable place fields within and across sessions. Place cells in otoconia-deficient tilted mice showed reduced spatial coherence and formed place fields that were located closer to environmental boundaries, relative to those of control mice. These differences reveal an important otolithic contribution to place-cell functioning and provide insight into the cognitive deficits associated with otolith dysfunction.
      Teaser Harvey et al. describe how place cells from otoconia-deficient mice become unstable across sessions and show a tendency to form place fields along environmental boundaries.

      PubDate: 2018-05-18T08:30:43Z
       
  • A GABAergic Feedback Shapes Dopaminergic Input on the Drosophila Mushroom
           Body to Promote Appetitive Long-Term Memory
    • Abstract: Publication date: Available online 17 May 2018
      Source:Current Biology
      Author(s): Alice Pavlowsky, Johann Schor, Pierre-Yves Plaçais, Thomas Preat
      Memory consolidation is a crucial step for long-term memory (LTM) storage. However, we still lack a clear picture of how memory consolidation is regulated at the neuronal circuit level. Here, we took advantage of the well-described anatomy of the Drosophila olfactory memory center, the mushroom body (MB), to address this question in the context of appetitive LTM. The MB lobes, which are made by the fascicled axons of the MB intrinsic neurons, are organized into discrete anatomical modules, each covered by the terminals of a defined type of dopaminergic neuron (DAN) and the dendrites of a corresponding type of MB output neuron (MBON). We previously revealed the essential role of one DAN, the MP1 neuron, in the formation of appetitive LTM. The MP1 neuron is anatomically matched to the GABAergic MBON MVP2, which has been attributed feedforward inhibitory functions recently. Here, we used behavior experiments and in vivo imaging to challenge the existence of MP1-MVP2 synapses and investigate their role in appetitive LTM consolidation. We show that MP1 and MVP2 neurons form an anatomically and functionally recurrent circuit, which features a feedback inhibition that regulates consolidation of appetitive memory. This circuit involves two opposite type 1 and type 2 dopamine receptors in MVP2 neurons and the metabotropic GABAB-R1 receptor in MP1 neurons. We propose that this dual-receptor feedback supports a bidirectional self-regulation of MP1 input to the MB. This mechanism displays striking similarities with the mammalian reward system, in which modulation of the dopaminergic signal is primarily assigned to inhibitory neurons.
      Teaser Pavlowsky et al. investigate the neuronal network at play during memory consolidation in Drosophila. They functionally characterize a feedback circuit between dopaminergic and GABAergic neurons that involves two antagonist dopamine receptors and a metabotropic GABA receptor. This circuit regulates olfactory long-term memory formation.

      PubDate: 2018-05-18T08:30:43Z
       
  • Short-Term, Intermittent Fasting Induces Long-Lasting Gut Health and
           TOR-Independent Lifespan Extension
    • Abstract: Publication date: Available online 17 May 2018
      Source:Current Biology
      Author(s): James H. Catterson, Mobina Khericha, Miranda C. Dyson, Alec J. Vincent, Rebecca Callard, Steven M. Haveron, Arjunan Rajasingam, Mumtaz Ahmad, Linda Partridge
      Intermittent fasting (IF) can improve function and health during aging in laboratory model organisms, but the mechanisms at work await elucidation. We subjected fruit flies (Drosophila melanogaster) to varying degrees of IF and found that just one month of a 2-day fed:5-day fasted IF regime at the beginning of adulthood was sufficient to extend lifespan. This long-lasting, beneficial effect of early IF was not due to reduced fecundity. Starvation resistance and resistance to oxidative and xenobiotic stress were increased after IF. Early-life IF also led to higher lipid content in 60-day-old flies, a potential explanation for increased longevity. Guts of flies 40 days post-IF showed a significant reduction in age-related pathologies and improved gut barrier function. Improved gut health was also associated with reduced relative bacterial abundance. Early IF thus induced profound long-term changes. Pharmacological and genetic epistasis analysis showed that IF acted independently of the TOR pathway because rapamycin and IF acted additively to extend lifespan, and global expression of a constitutively active S6K did not attenuate the IF-induced lifespan extension. We conclude that short-term IF during early life can induce long-lasting beneficial effects, with robust increase in lifespan in a TOR-independent manner, probably at least in part by preserving gut health.
      Graphical abstract image Teaser Intermittent fasting (IF) improves health and extends longevity in diverse model organisms. The fruit fly appeared to be the exception. Catterson et al. find that IF in early adulthood increases healthy lifespan of fruit flies. The effects of short-term IF are long-lasting, indicating that even brief IF periods may have lifelong health benefits.

      PubDate: 2018-05-18T08:30:43Z
       
  • The Maternal Effect Gene Wds Controls Wolbachia Titer in Nasonia
    • Abstract: Publication date: Available online 17 May 2018
      Source:Current Biology
      Author(s): Lisa J. Funkhouser-Jones, Edward J. van Opstal, Ananya Sharma, Seth R. Bordenstein
      Maternal transmission of intracellular microbes is pivotal in establishing long-term, intimate symbioses. For germline microbes that exert negative reproductive effects on their hosts, selection can theoretically favor the spread of host genes that counteract the microbe’s harmful effects. Here, we leverage a major difference in bacterial (Wolbachia pipientis) titers between closely related wasp species with forward genetic, transcriptomic, and cytological approaches to map two quantitative trait loci that suppress bacterial titers via a maternal effect. Fine mapping and knockdown experiments identify the gene Wolbachia density suppressor (Wds), which dominantly suppresses bacterial transmission from mother to embryo. Wds evolved by lineage-specific non-synonymous changes driven by positive selection. Collectively, our findings demonstrate that a genetically simple change arose by positive Darwinian selection in less than a million years to regulate maternally transmitted bacteria via a dominant, maternal effect gene.
      Graphical abstract image Teaser Funkhouser-Jones et al. use several forward genetic techniques to map two quantitative trait loci in the N. vitripennis genome, and they identify the taxon-restricted gene Wds, which strongly suppresses maternal transmission of Wolbachia to developing oocytes through a maternal genetic effect. The N. vitripennis Wds sequence evolved by positive Darwinian selection.

      PubDate: 2018-05-18T08:30:43Z
       
  • A Role for Mouse Primary Visual Cortex in Motion Perception
    • Abstract: Publication date: Available online 17 May 2018
      Source:Current Biology
      Author(s): Tiago Marques, Mathew T. Summers, Gabriela Fioreze, Marina Fridman, Rodrigo F. Dias, Marla B. Feller, Leopoldo Petreanu
      Visual motion is an ethologically important stimulus throughout the animal kingdom. In primates, motion perception relies on specific higher-order cortical regions. Although mouse primary visual cortex (V1) and higher-order visual areas show direction-selective (DS) responses, their role in motion perception remains unknown. Here, we tested whether V1 is involved in motion perception in mice. We developed a head-fixed discrimination task in which mice must report their perceived direction of motion from random dot kinematograms (RDKs). After training, mice made around 90% correct choices for stimuli with high coherence and performed significantly above chance for 16% coherent RDKs. Accuracy increased with both stimulus duration and visual field coverage of the stimulus, suggesting that mice in this task integrate motion information in time and space. Retinal recordings showed that thalamically projecting On-Off DS ganglion cells display DS responses when stimulated with RDKs. Two-photon calcium imaging revealed that neurons in layer (L) 2/3 of V1 display strong DS tuning in response to this stimulus. Thus, RDKs engage motion-sensitive retinal circuits as well as downstream visual cortical areas. Contralateral V1 activity played a key role in this motion direction discrimination task because its reversible inactivation with muscimol led to a significant reduction in performance. Neurometric-psychometric comparisons showed that an ideal observer could solve the task with the information encoded in DS L2/3 neurons. Motion discrimination of RDKs presents a powerful behavioral tool for dissecting the role of retino-forebrain circuits in motion processing.
      Teaser Using a head-fixed task, Marques et al. show that mice can discriminate the direction of motion of random dot kinetogram stimuli (RDK). RDKs elicit direction-selective responses in both On-Off DSGCs of the retina and in V1 L2/3 neurons. V1 inactivation impairs task performance, showing that this area plays a key role in motion perception.

      PubDate: 2018-05-18T08:30:43Z
       
  • Three-Dimensional Representation of Motor Space in the Mouse Superior
           Colliculus
    • Abstract: Publication date: Available online 17 May 2018
      Source:Current Biology
      Author(s): Jonathan J. Wilson, Nicolas Alexandre, Caterina Trentin, Marco Tripodi
      From the act of exploring an environment to that of grasping a cup of tea, animals must put in register their motor acts with their surrounding space. In the motor domain, this is likely to be defined by a register of three-dimensional (3D) displacement vectors, whose recruitment allows motion in the direction of a target. One such spatially targeted action is seen in the head reorientation behavior of mice, yet the neural mechanisms underlying these 3D behaviors remain unknown. Here, by developing a head-mounted inertial sensor for studying 3D head rotations and combining it with electrophysiological recordings, we show that neurons in the mouse superior colliculus are either individually or conjunctively tuned to the three Eulerian components of head rotation. The average displacement vectors associated with motor-tuned colliculus neurons remain stable over time and are unaffected by changes in firing rate or the duration of spike trains. Finally, we show that the motor tuning of collicular neurons is largely independent from visual or landmark cues. By describing the 3D nature of motor tuning in the superior colliculus, we contribute to long-standing debate on the dimensionality of collicular motor decoding; furthermore, by providing an experimental paradigm for the study of the metric of motor tuning in mice, this study also paves the way to the genetic dissection of the circuits underlying spatially targeted motion.
      Graphical abstract image Teaser Enacting spatially tuned movements requires a representational map of 3D motion vectors. Wilson et al. show that superior colliculus (SC) neurons are tuned to the full dimensionality of head rotations. Individual SC neurons code for preferred displacement angles, whereas their firing rates are further tuned to the angular velocity of movement.

      PubDate: 2018-05-18T08:30:43Z
       
  • Burst Firing in Bee Gustatory Neurons Prevents Adaptation
    • Abstract: Publication date: Available online 10 May 2018
      Source:Current Biology
      Author(s): Ashwin Miriyala, Sébastien Kessler, F. Claire Rind, Geraldine A. Wright
      Animals detect changes in the environment using modality-specific, peripheral sensory neurons. The insect gustatory system encodes tastant identity and concentration through the independent firing of gustatory receptor neurons (GRNs) that spike rapidly at stimulus onset and quickly adapt. Here, we show the first evidence that concentrated sugar evokes a temporally structured burst pattern of spiking involving two GRNs within the gustatory sensilla of bumblebees. Bursts of spikes resulted when a sucrose-activated GRN was inhibited by another GRN at a frequency of ∼22 Hz during the first 1 s of stimulation. Pharmacological blockade of gap junctions abolished bursting, indicating that bee GRNs have electrical synapses that produce a temporal pattern of spikes when one GRN is activated by a sugar ligand. Bursting permitted bee GRNs to maintain a high rate of spiking and to exhibit the slowest rate of adaptation of any insect species. Feeding bout duration correlated with coherent bursting; only sugar concentrations that produced bursting evoked the bumblebee’s feeding reflex. Volume of solution imbibed was a direct function of time in contact with food. We propose that gap junctions among GRNs enable a sustained rate of GRN spiking that is necessary to drive continuous feeding by the bee proboscis.
      Graphical abstract image Teaser Miriyala et al. discover that galeal sensilla on the bumblebee’s proboscis (mouthparts) have two gustatory receptor neurons (GRNs) that exhibit bursts of spikes in response to stimulation with sucrose. Bursting in these neurons depends on sugar value, is facilitated by gap junctions, and permits these neurons to resist sensory adaptation.

      PubDate: 2018-05-17T08:29:41Z
       
  • The Post-anaphase SUMO Pathway Ensures the Maintenance of Centromeric
           Cohesion through Meiosis I-II Transition in Mammalian Oocytes
    • Abstract: Publication date: Available online 10 May 2018
      Source:Current Biology
      Author(s): Yi Ding, Masako Kaido, Elena Llano, Alberto M. Pendas, Tomoya S. Kitajima
      The production of haploid gametes requires the maintenance of centromeric cohesion between sister chromatids through the transition between two successive meiotic divisions, meiosis I and meiosis II. One mechanism for the cohesion maintenance is shugoshin-dependent protection of centromeric cohesin at anaphase I onset [1–3]. However, how centromeric cohesion is maintained during late anaphase I and telophase I, when centromeric shugoshin is undetectable [1–3], remains largely unexplored. Here we show that the centromeric small ubiquitin-related modifier (SUMO) pathway is critical for the maintenance of centromeric cohesion during post-anaphase-I periods in mouse oocytes. SUMO2/3 and E3 ligase PIAS are enriched near centromeres during late anaphase I and telophase I. Specific perturbation of the centromeric SUMO pathway results in precocious loss of centromeric cohesin at telophase I, although shugoshin-dependent centromeric protection at anaphase I onset remains largely intact. Prevention of the SUMO perturbation during post-anaphase-I periods restores the maintenance of centromeric cohesion through the meiosis I-II transition. Thus, the post-anaphase-I centromeric SUMO pathway ensures continuous maintenance of centromeric cohesion through the meiosis I-II transition.
      Graphical abstract image Teaser Production of haploid gametes requires the maintenance of centromeric cohesion between sister chromatids through meiosis I-II transition. Ding et al. show that centromeric SUMOs are enriched during late anaphase I and telophase I, when the cohesion protector shugoshin Sgo2 is undetectable, and act to maintain centromeric cohesion in mouse oocytes.

      PubDate: 2018-05-17T08:29:41Z
       
  • Dynamic Fluctuations in Subcellular Localization of the Hippo Pathway
           Effector Yorkie In Vivo
    • Abstract: Publication date: Available online 10 May 2018
      Source:Current Biology
      Author(s): Samuel A. Manning, Lucas G. Dent, Shu Kondo, Ziqing W. Zhao, Nicolas Plachta, Kieran F. Harvey
      The Hippo pathway is an evolutionarily conserved signaling network that integrates diverse cues to control organ size and cell fate. The central downstream pathway protein in Drosophila is the transcriptional co-activator Yorkie (YAP and TAZ in humans), which regulates gene expression with the Scalloped/TEA domain family member (TEAD) transcription factors [1–8]. A central regulatory step in the Hippo pathway is phosphorylation of Yorkie by the NDR family kinase Warts, which promotes Yorkie cytoplasmic localization by stimulating association with 14-3-3 proteins [9–12]. Numerous reports have purported a static model of Hippo signaling whereby, upon Hippo activation, Yorkie/YAP/TAZ become cytoplasmic and therefore inactive, and upon Hippo repression, Yorkie/YAP/TAZ transit to the nucleus and are active. However, we have little appreciation for the dynamics of Yorkie/YAP/TAZ subcellular localization because most studies have been performed in fixed cells and tissues. To address this, we used live multiphoton microscopy to investigate the dynamics of an endogenously tagged Yorkie-Venus protein in growing epithelial organs. We found that the majority of Yorkie rapidly traffics between the cytoplasm and nucleus, rather than being statically localized in either compartment. In addition, discrete cell populations within the same organ display different rates of Yorkie nucleo-cytoplasmic shuttling. By assessing Yorkie dynamics in warts mutant tissue, we found that the Hippo pathway regulates Yorkie subcellular distribution by regulating its rate of nuclear import. Furthermore, Yorkie’s localization fluctuates dramatically throughout the cell cycle, being predominantly cytoplasmic during interphase and, unexpectedly, chromatin enriched during mitosis. Yorkie’s association with mitotic chromatin is Scalloped dependent, suggesting a potential role in mitotic bookmarking.
      Teaser Manning et al. investigate the subcellular dynamics of Yorkie, the key transcription regulator of the Hippo pathway, in vivo. They show that Yorkie is enriched on mitotic chromatin and that this depends on its DNA-binding partner, Scalloped. Yorkie nuclear import varies greatly across growing organs and is negatively regulated by the kinase Warts.

      PubDate: 2018-05-17T08:29:41Z
       
  • Replay of Episodic Memories in the Rat
    • Abstract: Publication date: Available online 10 May 2018
      Source:Current Biology
      Author(s): Danielle Panoz-Brown, Vishakh Iyer, Lawrence M. Carey, Christina M. Sluka, Gabriela Rajic, Jesse Kestenman, Meredith Gentry, Sydney Brotheridge, Isaac Somekh, Hannah E. Corbin, Kjersten G. Tucker, Bianca Almeida, Severine B. Hex, Krysten D. Garcia, Andrea G. Hohmann, Jonathon D. Crystal
      Vivid episodic memories in people have been characterized as the replay of multiple unique events in sequential order [1–3]. The hippocampus plays a critical role in episodic memories in both people and rodents [2, 4–6]. Although rats remember multiple unique episodes [7, 8], it is currently unknown if animals “replay” episodic memories. Therefore, we developed an animal model of episodic memory replay. Here, we show that rats can remember a trial-unique stream of multiple episodes and the order in which these events occurred by engaging hippocampal-dependent episodic memory replay. We document that rats rely on episodic memory replay to remember the order of events rather than relying on non-episodic memories. Replay of episodic memories survives a long retention-interval challenge and interference from the memory of other events, which documents that replay is part of long-term episodic memory. The chemogenetic activating drug clozapine N-oxide (CNO), but not vehicle, reversibly impairs episodic memory replay in rats previously injected bilaterally in the hippocampus with a recombinant viral vector containing an inhibitory designer receptor exclusively activated by a designer drug (DREADD; AAV8-hSyn-hM4Di-mCherry). By contrast, two non-episodic memory assessments are unaffected by CNO, showing selectivity of this hippocampal-dependent impairment. Our approach provides an animal model of episodic memory replay, a process by which the rat searches its representations in episodic memory in sequential order to find information. Our findings using rats suggest that the ability to replay a stream of episodic memories is quite old in the evolutionary timescale.
      Graphical abstract image Teaser Panoz-Brown et al. show that rats remember a stream of multiple episodes and the order in which they occur by engaging hippocampal-dependent episodic memory replay. They conclude that rats remember the order of events using episodic memory replay and that replay is part of long-term memory, resistant to interference, and hippocampal dependent.

      PubDate: 2018-05-17T08:29:41Z
       
  • Gigantism Precedes Filter Feeding in Baleen Whale Evolution
    • Abstract: Publication date: Available online 10 May 2018
      Source:Current Biology
      Author(s): R. Ewan Fordyce, Felix G. Marx
      Baleen whales (Mysticeti) are the largest animals on Earth, thanks to their ability to filter huge volumes of small prey from seawater. Mysticetes appeared during the Late Eocene, but evidence of their early evolution remains both sparse and controversial [1, 2], with several models competing to explain the origin of baleen-based bulk feeding [3–6]. Here, we describe a virtually complete skull of Llanocetus denticrenatus, the second-oldest (ca. 34 Ma) mysticete known. The new material represents the same individual as the type and only specimen, a fragmentary mandible. Phylogenetic analysis groups Llanocetus with the oldest mysticete, Mystacodon selenensis [2], into the basal family Llanocetidae. Llanocetus is gigantic (body length ∼8 m) compared to other early mysticetes [7–9]. The broad rostrum has sharp, widely spaced teeth with marked dental abrasion and attrition, suggesting biting and occlusal shearing. As in extant mysticetes, the palate bears many sulci, commonly interpreted as osteological correlates of baleen [3]. Unexpectedly, these sulci converge on the upper alveoli, suggesting a peri-dental blood supply to well-developed gums, rather than to inter-alveolar racks of baleen. We interpret Llanocetus as a raptorial or suction feeder, revealing that whales evolved gigantism well before the emergence of filter feeding. Rather than driving the origin of mysticetes, baleen and filtering most likely only arose after an initial phase of suction-assisted raptorial feeding [2, 4, 5]. This scenario differs strikingly from that proposed for odontocetes, whose defining adaptation—echolocation—was present even in their earliest representatives [10].
      Teaser Fordyce and Marx describe Llanocetus denticrenatus, the second-oldest baleen whale. Llanocetus has notably worn teeth and well-developed palatal blood vessels, consistent with large gums, but not baleen. Unlike their modern descendants, early whales most likely did not filter, but at least some of them still grew into giants.

      PubDate: 2018-05-17T08:29:41Z
       
  • Feedforward Inhibition Conveys Time-Varying Stimulus Information in a
           Collision Detection Circuit
    • Abstract: Publication date: Available online 10 May 2018
      Source:Current Biology
      Author(s): Hongxia Wang, Richard B. Dewell, Ying Zhu, Fabrizio Gabbiani
      Feedforward inhibition is ubiquitous as a motif in the organization of neuronal circuits. During sensory information processing, it is traditionally thought to sharpen the responses and temporal tuning of feedforward excitation onto principal neurons. As it often exhibits complex time-varying activation properties, feedforward inhibition could also convey information used by single neurons to implement dendritic computations on sensory stimulus variables. We investigated this possibility in a collision-detecting neuron of the locust optic lobe that receives both feedforward excitation and inhibition. We identified a small population of neurons mediating feedforward inhibition, with wide visual receptive fields and whose responses depend both on the size and speed of moving stimuli. By studying responses to simulated objects approaching on a collision course, we determined that they jointly encode the angular size of expansion of the stimulus. Feedforward excitation, on the other hand, encodes a function of the angular velocity of expansion and the targeted collision-detecting neuron combines these two variables non-linearly in its firing output. Thus, feedforward inhibition actively contributes to the detailed firing-rate time course of this collision-detecting neuron, a feature critical to the appropriate execution of escape behaviors. These results suggest that feedforward inhibition could similarly convey time-varying stimulus information in other neuronal circuits.
      Teaser In the locust visual system, Wang et al. identify inhibitory neurons that encode the angular size of simulated objects approaching on a collision course. This shows that inhibitory neurons provide time-varying information on spatially extended stimuli and contribute to neuronal computations involved in collision avoidance behaviors.

      PubDate: 2018-05-17T08:29:41Z
       
  • nocte Is Required for Integrating Light and Temperature Inputs in
           Circadian Clock Neurons of Drosophila
    • Abstract: Publication date: Available online 10 May 2018
      Source:Current Biology
      Author(s): Chenghao Chen, Min Xu, Yuto Anantaprakorn, Mechthild Rosing, Ralf Stanewsky
      Circadian clocks organize biological processes to occur at optimized times of day and thereby contribute to overall fitness. While the regular daily changes of environmental light and temperature synchronize circadian clocks, extreme external conditions can bypass the temporal constraints dictated by the clock. Despite advanced knowledge about how the daily light-dark changes synchronize the clock, relatively little is known with regard to how the daily temperature changes influence daily timing and how temperature and light signals are integrated. In Drosophila, a network of ∼150 brain clock neurons exhibit 24-hr oscillations of clock gene expression to regulate daily activity and sleep. We show here that a temperature input pathway from peripheral sensory organs, which depends on the gene nocte, targets specific subsets of these clock neurons to synchronize molecular and behavioral rhythms to temperature cycles. Strikingly, while nocte 1 mutant flies synchronize normally to light-dark cycles at constant temperatures, the combined presence of light-dark and temperature cycles inhibits synchronization. nocte 1 flies exhibit altered siesta sleep, suggesting that the sleep-regulating clock neurons are an important target for nocte-dependent temperature input, which dominates a parallel light input into these cells. In conclusion, we reveal a nocte-dependent temperature input pathway to central clock neurons and show that this pathway and its target neurons are important for the integration of sensory light and temperature information in order to temporally regulate activity and sleep during daily light and temperature cycles.
      Graphical abstract image Teaser Temperature synchronization of the fly circadian clock involves nocte-dependent sensory input. Chen et al. show that this thermal input targets specific brain clock neurons. Surprisingly, nocte is also important for synchronization to combined light and temperature cycles as they occur in nature—and hence for integration of different sensory cues.

      PubDate: 2018-05-17T08:29:41Z
       
  • Host Energy Source Is Important for Disease Tolerance to Malaria
    • Abstract: Publication date: Available online 10 May 2018
      Source:Current Biology
      Author(s): Katherine Cumnock, Avni S. Gupta, Michelle Lissner, Victoria Chevee, Nicole M. Davis, David S. Schneider
      Pathologic infections are accompanied by a collection of short-term behavioral perturbations collectively termed sickness behaviors [1, 2]. These include changes in body temperature, reduced eating and drinking, and lethargy and mimic behaviors of animals in torpor and hibernation [1, 3–6]. Sickness behaviors are important, pathogen-specific components of the host response to infection [1, 3, 7–9]. In particular, host anorexia has been shown to be beneficial or detrimental depending on the infection [7, 8]. While these studies have illuminated the effects of anorexia on infection, they consider this behavior in isolation from other behaviors and from its effects on host metabolism and energy. Here, we explored the temporal dynamics of multiple sickness behaviors and their effect on host energy and metabolism throughout infection. We used the Plasmodium chabaudi AJ murine model of malaria as it causes severe pathology from which most animals recover. We found that infected animals did become anorexic, skewing their metabolism toward fatty acid oxidation and ketosis. Metabolism of fats requires oxygen for the production of ATP. In this model, animals also suffer severe anemia, limiting their ability to carry oxygen concurrent with their switch toward fatty acid metabolism. We reasoned that the combination of anorexia and anemia would increase pressure on glycolysis as a critical energy pathway because it does not require oxygen. Treating infected mice when anorexic with the glycolytic inhibitor 2-deoxyglucose (2DG) reduced survival; treating animals with glucose improved survival. Peak parasite loads were unchanged, demonstrating changes in disease tolerance. Parasite clearance was reduced with 2DG treatment, suggesting altered resistance.
      Teaser Cumnock et al. find that mice suffering from malaria face metabolic challenges created by their symptoms. The mice become anorexic and try to burn fat, requiring oxygen. The mice also become anemic, limiting oxygen transport. This suggests that glycolysis is a critical energy pathway. Manipulation of glycolysis modulates survival of the infected mice.

      PubDate: 2018-05-17T08:29:41Z
       
  • Watching two billion people
    • Abstract: Publication date: 7 May 2018
      Source:Current Biology, Volume 28, Issue 9
      Author(s): Michael Gross
      The global use of the internet and social media platforms like Facebook offers unprecedented opportunities to study human behaviour with the help of big data and automated investigations. However, as recent events demonstrate, similar approaches can also be misused to manipulate people and political processes. New ethical norms may be required. Michael Gross reports.
      Teaser The global use of the internet and social media platforms like Facebook offers unprecedented opportunities to study human behaviour with the help of big data and automated investigations. However, as recent events demonstrate, similar approaches can also be misused to manipulate people and political processes. New ethical norms may be required.

      PubDate: 2018-05-17T08:29:41Z
       
  • Seeds: more than meets the eye
    • Abstract: Publication date: 7 May 2018
      Source:Current Biology, Volume 28, Issue 9
      Author(s): Stephen A. Harris


      PubDate: 2018-05-17T08:29:41Z
       
  • Are the ghosts of nature’s past haunting ecology today'
    • Abstract: Publication date: 7 May 2018
      Source:Current Biology, Volume 28, Issue 9
      Author(s): Brian R. Silliman, Brent B. Hughes, Lindsay C. Gaskins, Qiang He, M. Tim Tinker, Andrew Read, James Nifong, Rick Stepp
      Humans have decimated populations of large-bodied consumers and their functions in most of the world’s ecosystems. It is less clear how human activities have affected the diversity of habitats these consumers occupy. Rebounding populations of some predators after conservation provides an opportunity to begin to investigate this question. Recent research shows that following long-term protection, sea otters along the northeast Pacific coast have expanded into estuarine marshes and seagrasses, and alligators on the southeast US coast have expanded into saltwater ecosystems, habitats presently thought beyond their niche space. There is also evidence that seals have expanded into subtropical climates, mountain lions into grasslands, orangutans into disturbed forests and wolves into coastal marine ecosystems. Historical records, surveys of protected areas and patterns of animals moving into habitats that were former hunting hotspots indicate that — rather than occupying them for the first time — many of these animals are in fact recolonizing ecosystems. Recognizing that many large consumers naturally live and thrive across a greater diversity of ecosystems has implications for setting historical baselines for predator diversity within specific habitats, enhancing the resilience of newly colonized ecosystems and for plans to recover endangered species, as a greater range of habitats is available for large consumers as refugia from climate-induced threats.
      Teaser Silliman et al. discuss the ecological and conservation implications of predators showing-up and thriving in ecosystems thought beyond their niche space

      PubDate: 2018-05-17T08:29:41Z
       
  • Barbara Webb
    • Abstract: Publication date: 7 May 2018
      Source:Current Biology, Volume 28, Issue 9
      Author(s): Barbara Webb
      Teaser Interview with Barbara Webb, who uses robots to model the behavioural capabilities of insects at the University of Edinburgh.

      PubDate: 2018-05-17T08:29:41Z
       
  • MICALs
    • Abstract: Publication date: 7 May 2018
      Source:Current Biology, Volume 28, Issue 9
      Author(s): Laura Taylor Alto, Jonathan R. Terman
      Teaser Alto and Terman introduce the MICAL family of actin regulatory redox enzymes.

      PubDate: 2018-05-17T08:29:41Z
       
  • Tropical savannas and dry forests
    • Abstract: Publication date: 7 May 2018
      Source:Current Biology, Volume 28, Issue 9
      Author(s): R. Toby Pennington, Caroline E.R. Lehmann, Lucy M. Rowland
      In the tropics, research, conservation and public attention focus on rain forests, but this neglects that half of the global tropics have a seasonally dry climate. These regions are home to dry forests and savannas (Figures 1 and 2), and are the focus of this Primer. The attention given to rain forests is understandable. Their high species diversity, sheer stature and luxuriance thrill biologists today as much as they did the first explorers in the Age of Discovery. Although dry forest and savanna may make less of a first impression, they support a fascinating diversity of plant strategies to cope with stress and disturbance including fire, drought and herbivory. Savannas played a fundamental role in human evolution, and across Africa and India they support iconic megafauna.
      Teaser Pennington et al. introduce seasonally dry biomes in the tropics – savannahs and dry forests.

      PubDate: 2018-05-17T08:29:41Z
       
  • Vergence eye movements direct others’ attention in three-dimensional
           space
    • Abstract: Publication date: 7 May 2018
      Source:Current Biology, Volume 28, Issue 9
      Author(s): A.T.T. Nguyen, C.J. Palmer, C.W.G. Clifford
      Vision is an active sense and, as we explore the world with our eyes, the direction of our gaze provides others a signal as to the focus of our attention [1,2]. Research in experimental psychology has established that others’ direction of gaze reflexively guides our attention within our visual field [3,4], serving as a crucial social cue when coordinating attention with others during joint action and word–object association learning [2]. A forward-facing pair of eyes in humans and other animals not only enables us to converge our gaze to the precise depth at which an object is located, but also potentially informs others about how far away we are looking. But very little is known about the perception of others’ gaze vergence, and whether the vergence of an individual’s eyes can be used by others to determine the precise focus of that person’s attention in three-dimensional space. Here, we applied an attentional orienting paradigm in a three-dimensional stereoscopic setting and found that observers consistently detect targets more quickly when they are at a depth congruent with another person’s eye vergence compared to when they are at an incongruent depth. These findings reveal that our representation of others’ gaze is specific not just to their line of sight [5,6] but rather to particular locations in three-dimensional space signalled by eye vergence.
      Teaser Eye gaze is an important cue in social communication: the vergence of others’ eyes can potentially inform us of the distance at which they are fixating. Nguyen et al. use an attentional orienting paradigm in a three-dimensional stereoscopic setting to show that vergence eye movements can automatically cue our attention to locations in three-dimensional space that differ in depth.

      PubDate: 2018-05-17T08:29:41Z
       
  • Classifying elephant behaviour through seismic vibrations
    • Abstract: Publication date: 7 May 2018
      Source:Current Biology, Volume 28, Issue 9
      Author(s): Beth Mortimer, William Lake Rees, Paula Koelemeijer, Tarje Nissen-Meyer
      Seismic waves — vibrations within and along the Earth’s surface — are ubiquitous sources of information. During propagation, physical factors can obscure information transfer via vibrations and influence propagation range [1]. Here, we explore how terrain type and background seismic noise influence the propagation of seismic vibrations generated by African elephants. In Kenya, we recorded the ground-based vibrations of different wild elephant behaviours, such as locomotion and infrasonic vocalisations [2], as well as natural and anthropogenic seismic noise. We employed techniques from seismology to transform the geophone recordings into source functions — the time-varying seismic signature generated at the source. We used computer modelling to constrain the propagation ranges of elephant seismic vibrations for different terrains and noise levels. Behaviours that generate a high force on a sandy terrain with low noise propagate the furthest, over the kilometre scale. Our modelling also predicts that specific elephant behaviours can be distinguished and monitored over a range of propagation distances and noise levels. We conclude that seismic cues have considerable potential for both behavioural classification and remote monitoring of wildlife. In particular, classifying the seismic signatures of specific behaviours of large mammals remotely in real time, such as elephant running, could inform on poaching threats.
      Teaser Mortimer et al. explore elephant seismic vibrations. Combining computer modelling and field experiments, they show that behaviour, terrain and noise interact to affect the propagation of seismic information. Elephant behaviours generating high forces were predicted to travel farthest and could be used by researchers to remotely monitor wildlife.

      PubDate: 2018-05-17T08:29:41Z
       
  • Human Genetics: Busy Subway Networks in Remote Oceania'
    • Abstract: Publication date: 7 May 2018
      Source:Current Biology, Volume 28, Issue 9
      Author(s): Anders Bergström, Chris Tyler-Smith
      Ancient human DNA from the Oceanian islands of Vanuatu reveals a surprisingly complex history of human settlement, featuring almost complete replacement shortly after initial colonisation, followed by mixing and a puzzling disconnect between genetic ancestry and language.
      Teaser Ancient human DNA from the Oceanian islands of Vanuatu reveals a surprisingly complex history of human settlement, featuring almost complete replacement shortly after initial colonisation, followed by mixing and a puzzling disconnect between genetic ancestry and language

      PubDate: 2018-05-17T08:29:41Z
       
  • Stomatal Physiology: Cereal Successes
    • Abstract: Publication date: 7 May 2018
      Source:Current Biology, Volume 28, Issue 9
      Author(s): Colin Brownlee
      The grasses have been extremely successful in colonizing a wide range of terrestrial habitats, partially due to the unique physiology of their stomatal complexes. A new study has added new insight into the regulation of cereal stomata in showing that they are sensitive to nitrate concentration, and how a specific anion channel is responsible for this sensitivity.
      Teaser The grasses have been extremely successful in colonizing a wide range of terrestrial habitats, partially due to the unique physiology of their stomatal complexes. A new study has added new insight into the regulation of cereal stomata in showing that they are sensitive to nitrate concentration, and how a specific anion channel is responsible for this sensitivity.

      PubDate: 2018-05-17T08:29:41Z
       
  • Social Behavior: Developmental Timing Defies Puberty
    • Abstract: Publication date: 7 May 2018
      Source:Current Biology, Volume 28, Issue 9
      Author(s): Brian J. Prendergast, Irving Zucker
      A closer look at behavioral development in seasonally breeding rodents reveals more complex relations between puberty and social behavior than previously recognized. Pubertal hormones determine gross amounts of behavior, but play recedes and aggression emerges independently of puberty at predetermined chronological ages.
      Teaser A closer look at behavioral development in seasonally breeding rodents reveals more complex relations between puberty and social behavior than previously recognized. Pubertal hormones determine gross amounts of behavior, but play recedes and aggression emerges independently of puberty at predetermined chronological ages

      PubDate: 2018-05-17T08:29:41Z
       
  • Word Learning: Associations or Hypothesis Testing'
    • Abstract: Publication date: 7 May 2018
      Source:Current Biology, Volume 28, Issue 9
      Author(s): George Kachergis
      Children learn thousands of words in the first years of life, but the process supporting this feat is largely unknown. New neuroimaging results indicate that learning a word may be sudden rather than gradual, supported by hippocampal memory.
      Teaser Children learn thousands of words in the first years of life, but the process supporting this feat is largely unknown. New neuroimaging results indicate that learning a word may be sudden rather than gradual, supported by hippocampal memory.

      PubDate: 2018-05-17T08:29:41Z
       
  • Sleep: Short Sleepers Should Keep Count of Their Hypocretin Neurons
    • Abstract: Publication date: 7 May 2018
      Source:Current Biology, Volume 28, Issue 9
      Author(s): Louis C. Leung, Philippe Mourrain
      Sleep durations vary greatly across animals from 2 to 20 hours with no clear explanation. A small Mexican cavefish reveals how the brain can adapt to increase its wake-stabilizing hypocretin circuit and dramatically reduce sleep, likely to allow adaptive foraging.
      Teaser Sleep durations vary greatly across animals from 2 to 20 hours with no clear explanation. A small Mexican cavefish reveals how the brain can adapt to increase its wake-stabilizing hypocretin circuit and dramatically reduce sleep, likely to allow adaptive foraging.

      PubDate: 2018-05-17T08:29:41Z
       
  • Toxicology: Bee P450s Take the Sting out of Cyanoamidine Neonicotinoids
    • Abstract: Publication date: 7 May 2018
      Source:Current Biology, Volume 28, Issue 9
      Author(s): René Feyereisen
      The neonicotinoid insecticides have raised concerns regarding the health of bee pollinators. New research has identified a P450 enzyme that protects honey bees and bumble bees from the toxicity of two neonicotinoids, thiacloprid and acetamiprid. This P450 enzyme provides a margin of safety to bees.
      Teaser The neonicotinoid insecticides have raised concerns regarding the health of bee pollinators. New research has identified a P450 enzyme that protects honey bees and bumble bees from the toxicity of two neonicotinoids, thiacloprid and acetamiprid. This P450 enzyme provides a margin of safety to bees.

      PubDate: 2018-05-17T08:29:41Z
       
  • Gut Immunity: Passing on the Baton from Innate to Adaptive Immunity
    • Abstract: Publication date: 7 May 2018
      Source:Current Biology, Volume 28, Issue 9
      Author(s): Nora Branzk, Andreas Diefenbach
      Innate and adaptive immunity are two complementary systems that work together to protect the host organism. A new study unravels how innate lymphoid cells and adaptive T lymphocytes act sequentially to establish microbial commensalism and ensure tissue and metabolic homeostasis.
      Teaser Innate and adaptive immunity are two complementary systems that work together to protect the host organism. A new study unravels how innate lymphoid cells and adaptive T lymphocytes act sequentially to establish microbial commensalism and ensure tissue and metabolic homeostasis.

      PubDate: 2018-05-17T08:29:41Z
       
  • Evolution: An Archipelago Replete with Replicates
    • Abstract: Publication date: 7 May 2018
      Source:Current Biology, Volume 28, Issue 9
      Author(s): Moritz Muschick, Walter Salzburger
      Adaptive radiations, in which repeated bouts of diversification lead to phenotypically similar species, highlight the power of natural selection and predictability in evolution. A newly discovered radiation of stick spiders on Hawaii helps shed new light on this phenomenon.
      Teaser Adaptive radiations, in which repeated bouts of diversification lead to phenotypically similar species, highlight the power of natural selection and predictability in evolution. A newly discovered radiation of stick spiders on Hawaii helps shed new light on this phenomenon.

      PubDate: 2018-05-17T08:29:41Z
       
  • Left–Right Asymmetry: Myosin 1D at the Center
    • Abstract: Publication date: 7 May 2018
      Source:Current Biology, Volume 28, Issue 9
      Author(s): Shiaulou Yuan, Martina Brueckner
      While a ciliated organizer generates vertebrate left–right asymmetry, most invertebrates lack an organizer and instead utilize a myosin-based mechanism. A recent study now reveals that this myosin mechanism is conserved in the vertebrate organizer and functions to regulate cilia.
      Teaser While a ciliated organizer generates vertebrate left–right asymmetry, most invertebrates lack an organizer and instead utilize a myosin-based mechanism. A recent study now reveals that this myosin mechanism is conserved in the vertebrate organizer and functions to regulate cilia.

      PubDate: 2018-05-17T08:29:41Z
       
  • Spatiotemporal Regulation of RhoA during Cytokinesis
    • Abstract: Publication date: 7 May 2018
      Source:Current Biology, Volume 28, Issue 9
      Author(s): Angika Basant, Michael Glotzer
      The active form of the small GTPase RhoA is necessary and sufficient for formation of a cytokinetic furrow in animal cells. Despite the conceptual simplicity of the process, the molecular mechanisms that control it are intricate and involve redundancy at multiple levels. Here, we discuss our current knowledge of the mechanisms underlying spatiotemporal regulation of RhoA during cytokinesis by upstream activators. The direct upstream activator, the RhoGEF Ect2, requires activation due to autoinhibition. Ect2 is primarily activated by the centralspindlin complex, which contains numerous domains that regulate its subcellular localization, oligomeric state, and Ect2 activation. We review the functions of these domains and how centralspindlin is regulated to ensure correctly timed, equatorial RhoA activation. Highlighting recent evidence, we propose that although centralspindlin does not always prominently accumulate on the plasma membrane, it is the site where it promotes RhoA activation during cytokinesis.
      Teaser Basant and Glotzer review how RhoA activity is regulated to ensure correct timing and placement of cytokinesis.

      PubDate: 2018-05-17T08:29:41Z
       
  • Novelty-Sensitive Dopaminergic Neurons in the Human Substantia Nigra
           Predict Success of Declarative Memory Formation
    • Abstract: Publication date: 7 May 2018
      Source:Current Biology, Volume 28, Issue 9
      Author(s): Jan Kamiński, Adam N. Mamelak, Kurtis Birch, Clayton P. Mosher, Michele Tagliati, Ueli Rutishauser
      The encoding of information into long-term declarative memory is facilitated by dopamine. This process depends on hippocampal novelty signals, but it remains unknown how midbrain dopaminergic neurons are modulated by declarative-memory-based information. We recorded individual substantia nigra (SN) neurons and cortical field potentials in human patients performing a recognition memory task. We found that 25% of SN neurons were modulated by stimulus novelty. Extracellular waveform shape and anatomical location indicated that these memory-selective neurons were putatively dopaminergic. The responses of memory-selective neurons appeared 527 ms after stimulus onset, changed after a single trial, and were indicative of recognition accuracy. SN neurons phase locked to frontal cortical theta-frequency oscillations, and the extent of this coordination predicted successful memory formation. These data reveal that dopaminergic neurons in the human SN are modulated by memory signals and demonstrate a progression of information flow in the hippocampal-basal ganglia-frontal cortex loop for memory encoding.
      Teaser Kamiński et al. show that human substantia nigra neurons are modulated by stimulus novelty and that phase locking of these neurons to frontal cortical oscillations predicts memory formation. These findings provide direct single-neuron evidence for the engagement of the dopamine system in human declarative memory formation.

      PubDate: 2018-05-17T08:29:41Z
       
  • A Forward Genetic Screen in Zebrafish Identifies the G-Protein-Coupled
           Receptor CaSR as a Modulator of Sensorimotor Decision Making
    • Abstract: Publication date: 7 May 2018
      Source:Current Biology, Volume 28, Issue 9
      Author(s): Roshan A. Jain, Marc A. Wolman, Kurt C. Marsden, Jessica C. Nelson, Hannah Shoenhard, Fabio A. Echeverry, Christina Szi, Hannah Bell, Julianne Skinner, Emilia N. Cobbs, Keisuke Sawada, Amy D. Zamora, Alberto E. Pereda, Michael Granato
      Animals continuously integrate sensory information and select contextually appropriate responses. Here, we show that zebrafish larvae select a behavioral response to acoustic stimuli from a pre-existing choice repertoire in a context-dependent manner. We demonstrate that this sensorimotor choice is modulated by stimulus quality and history, as well as by neuromodulatory systems—all hallmarks of more complex decision making. Moreover, from a genetic screen coupled with whole-genome sequencing, we identified eight mutants with deficits in this sensorimotor choice, including mutants of the vertebrate-specific G-protein-coupled extracellular calcium-sensing receptor (CaSR), whose function in the nervous system is not well understood. We demonstrate that CaSR promotes sensorimotor decision making acutely through Gαi/o and Gαq/11 signaling, modulated by clathrin-mediated endocytosis. Combined, our results identify the first set of genes critical for behavioral choice modulation in a vertebrate and reveal an unexpected critical role for CaSR in sensorimotor decision making.
      Graphical abstract image Teaser Using larval zebrafish, Jain et al. establish and validate a simple sensorimotor decision-making paradigm. Using this paradigm, they perform a forward genetic screen that identifies the first set of vertebrate sensorimotor decision-making genes, including the calcium-sensing receptor, which acts as a bidirectional regulator of sensorimotor choice.

      PubDate: 2018-05-17T08:29:41Z
       
  • A Tandem Amino Acid Residue Motif in Guard Cell SLAC1 Anion Channel of
           Grasses Allows for the Control of Stomatal Aperture by Nitrate
    • Abstract: Publication date: 7 May 2018
      Source:Current Biology, Volume 28, Issue 9
      Author(s): Nadine Schäfer, Tobias Maierhofer, Johannes Herrmann, Morten Egevang Jørgensen, Christof Lind, Katharina von Meyer, Silke Lautner, Jörg Fromm, Marius Felder, Alistair M. Hetherington, Peter Ache, Dietmar Geiger, Rainer Hedrich
      The latest major group of plants to evolve were the grasses. These became important in the mid-Paleogene about 40 million years ago. During evolution, leaf CO2 uptake and transpirational water loss were optimized by the acquisition of grass-specific stomatal complexes. In contrast to the kidney-shaped guard cells (GCs) typical of the dicots such as Arabidopsis, in the grasses and agronomically important cereals, the GCs are dumbbell shaped and are associated with morphologically distinct subsidiary cells (SCs). We studied the molecular basis of GC action in the major cereal crop barley. Upon feeding ABA to xylem sap of an intact barley leaf, stomata closed in a nitrate-dependent manner. This process was initiated by activation of GC SLAC-type anion channel currents. HvSLAC1 expressed in Xenopus oocytes gave rise to S-type anion currents that increased several-fold upon stimulation with >3 mM nitrate. We identified a tandem amino acid residue motif that within the SLAC1 channels differs fundamentally between monocots and dicots. When the motif of nitrate-insensitive dicot Arabidopsis SLAC1 was replaced by the monocot signature, AtSLAC1 converted into a grass-type like nitrate-sensitive channel. Our work reveals a fundamental difference between monocot and dicot GCs and prompts questions into the selective pressures during evolution that resulted in fundamental changes in the regulation of SLAC1 function.
      Graphical abstract image Teaser Schäfer et al. report that guard cells of the cereal crop barley require nitrate for ABA-induced stomatal closure—a feature accomplished by the guard cell anion channel HvSLAC1. Nitrate-dependent gating of HvSLAC1 and other monocot SLAC1-type anion channels evolved from a TMD3 tandem motif after the split between monocots and dicots.

      PubDate: 2018-05-17T08:29:41Z
       
  • Phasic Dopamine Signals in the Nucleus Accumbens that Cause Active
           Avoidance Require Endocannabinoid Mobilization in the Midbrain
    • Abstract: Publication date: 7 May 2018
      Source:Current Biology, Volume 28, Issue 9
      Author(s): Jennifer M. Wenzel, Erik B. Oleson, Willard N. Gove, Anthony B. Cole, Utsav Gyawali, Hannah M. Dantrassy, Rebecca J. Bluett, Dilyan I. Dryanovski, Garret D. Stuber, Karl Deisseroth, Brian N. Mathur, Sachin Patel, Carl R. Lupica, Joseph F. Cheer
      Phasic dopamine (DA) release accompanies approach toward appetitive cues. However, a role for DA in the active avoidance of negative events remains undetermined. Warning signals informing footshock avoidance are associated with accumbal DA release, whereas depression of DA is observed with unavoidable footshock. Here, we reveal a causal role of phasic DA in active avoidance learning; specifically, optogenetic activation of DA neurons facilitates avoidance, whereas optical inhibition of these cells attenuates it. Furthermore, stimulation of DA neurons during presentation of a fear-conditioned cue accelerates the extinction of a passive defensive behavior (i.e., freezing). Dopaminergic control of avoidance requires endocannabinoids (eCBs), as perturbing eCB signaling in the midbrain disrupts avoidance, which is rescued by optical stimulation of DA neurons. Interestingly, once the avoidance task is learned, neither DA nor eCB manipulations affect performance, suggesting that once acquisition occurs, expression of this behavior is subserved by other anatomical frameworks. Our findings establish an instrumental role for DA release in learning active responses to aversive stimuli and its control by eCB signaling.
      Teaser Wenzel et al. demonstrate that phasic mesolimbic dopamine promotes behavior motivated by a cue that predicts a negative event. This dopamine signal is controlled by midbrain endocannabinoids. However, once this behavior is well learned, it becomes independent of these systems.

      PubDate: 2018-05-17T08:29:41Z
       
  • Adaptive and Selective Time Averaging of Auditory Scenes
    • Abstract: Publication date: 7 May 2018
      Source:Current Biology, Volume 28, Issue 9
      Author(s): Richard McWalter, Josh H. McDermott
      To overcome variability, estimate scene characteristics, and compress sensory input, perceptual systems pool data into statistical summaries. Despite growing evidence for statistical representations in perception, the underlying mechanisms remain poorly understood. One example of such representations occurs in auditory scenes, where background texture appears to be represented with time-averaged sound statistics. We probed the averaging mechanism using “texture steps”—textures containing subtle shifts in stimulus statistics. Although generally imperceptible, steps occurring in the previous several seconds biased texture judgments, indicative of a multi-second averaging window. Listeners seemed unable to willfully extend or restrict this window but showed signatures of longer integration times for temporally variable textures. In all cases the measured timescales were substantially longer than previously reported integration times in the auditory system. Integration also showed signs of being restricted to sound elements attributed to a common source. The results suggest an integration process that depends on stimulus characteristics, integrating over longer extents when it benefits statistical estimation of variable signals and selectively integrating stimulus components likely to have a common cause in the world. Our methodology could be naturally extended to examine statistical representations of other types of sensory signals.
      Teaser Sound texture perception is thought to be mediated by time-averaged sound statistics. McWalter and McDermott use texture “steps” to reveal an obligatory multi-second averaging process whose extent depends on texture variability. Averaging excludes other concurrent sounds, implicating texture perception as inseparable from auditory scene analysis.

      PubDate: 2018-05-17T08:29:41Z
       
  • Tracing the Trajectory of Sensory Plasticity across Different Stages of
           Speech Learning in Adulthood
    • Abstract: Publication date: 7 May 2018
      Source:Current Biology, Volume 28, Issue 9
      Author(s): Rachel Reetzke, Zilong Xie, Fernando Llanos, Bharath Chandrasekaran
      Although challenging, adults can learn non-native phonetic contrasts with extensive training [1, 2], indicative of perceptual learning beyond an early sensitivity period [3, 4]. Training can alter low-level sensory encoding of newly acquired speech sound patterns [5]; however, the time-course, behavioral relevance, and long-term retention of such sensory plasticity is unclear. Some theories argue that sensory plasticity underlying signal enhancement is immediate and critical to perceptual learning [6, 7]. Others, like the reverse hierarchy theory (RHT), posit a slower time-course for sensory plasticity [8]. RHT proposes that higher-level categorical representations guide immediate, novice learning, while lower-level sensory changes do not emerge until expert stages of learning [9]. We trained 20 English-speaking adults to categorize a non-native phonetic contrast (Mandarin lexical tones) using a criterion-dependent sound-to-category training paradigm. Sensory and perceptual indices were assayed across operationally defined learning phases (novice, experienced, over-trained, and 8-week retention) by measuring the frequency-following response, a neurophonic potential that reflects fidelity of sensory encoding, and the perceptual identification of a tone continuum. Our results demonstrate that while robust changes in sensory encoding and perceptual identification of Mandarin tones emerged with training and were retained, such changes followed different timescales. Sensory changes were evidenced and related to behavioral performance only when participants were over-trained. In contrast, changes in perceptual identification reflecting improvement in categorical percept emerged relatively earlier. Individual differences in perceptual identification, and not sensory encoding, related to faster learning. Our findings support the RHT—sensory plasticity accompanies, rather than drives, expert levels of non-native speech learning.
      Teaser Reetzke et al. show that as adults are trained to categorize non-native speech sounds, sensory encoding of non-native speech sound patterns improves only after an expert level of behavioral performance. Training-induced changes in sensory encoding relate to behavioral performance and endure beyond the period of training.

      PubDate: 2018-05-17T08:29:41Z
       
  • Decodability of Reward Learning Signals Predicts Mood Fluctuations
    • Abstract: Publication date: 7 May 2018
      Source:Current Biology, Volume 28, Issue 9
      Author(s): Eran Eldar, Charlotte Roth, Peter Dayan, Raymond J. Dolan
      Our mood often fluctuates without warning. Recent accounts propose that these fluctuations might be preceded by changes in how we process reward. According to this view, the degree to which reward improves our mood reflects not only characteristics of the reward itself (e.g., its magnitude) but also how receptive to reward we happen to be. Differences in receptivity to reward have been suggested to play an important role in the emergence of mood episodes in psychiatric disorders [1–16]. However, despite substantial theory, the relationship between reward processing and daily fluctuations of mood has yet to be tested directly. In particular, it is unclear whether the extent to which people respond to reward changes from day to day and whether such changes are followed by corresponding shifts in mood. Here, we use a novel mobile-phone platform with dense data sampling and wearable heart-rate and electroencephalographic sensors to examine mood and reward processing over an extended period of one week. Subjects regularly performed a trial-and-error choice task in which different choices were probabilistically rewarded. Subjects’ choices revealed two complementary learning processes, one fast and one slow. Reward prediction errors [17, 18] indicative of these two processes were decodable from subjects’ physiological responses. Strikingly, more accurate decodability of prediction-error signals reflective of the fast process predicted improvement in subjects’ mood several hours later, whereas more accurate decodability of the slow process’ signals predicted better mood a whole day later. We conclude that real-life mood fluctuations follow changes in responsivity to reward at multiple timescales.
      Teaser In a week-long smartphone experiment, Eldar et al. show that reward-prediction errors indicative of fast and slow reward-learning processes can be decoded from EEG and heart-rate signals. Moreover, fast and slow mood fluctuations are predicted by how well fast and slow learning can be decoded—positive mood changes follow greater decodabilities.

      PubDate: 2018-05-17T08:29:41Z
       
  • Ejaculation Induced by the Activation of Crz Neurons Is Rewarding to
           Drosophila Males
    • Abstract: Publication date: 7 May 2018
      Source:Current Biology, Volume 28, Issue 9
      Author(s): Shir Zer-Krispil, Hila Zak, Lisha Shao, Shir Ben-Shaanan, Lea Tordjman, Assa Bentzur, Anat Shmueli, Galit Shohat-Ophir
      The reward system is a collection of circuits that reinforce behaviors necessary for survival [1, 2]. Given the importance of reproduction for survival, actions that promote successful mating induce pleasurable feeling and are positively reinforced [3, 4]. This principle is conserved in Drosophila, where successful copulation is naturally rewarding to male flies, induces long-term appetitive memories [5], increases brain levels of neuropeptide F (NPF, the fly homolog of neuropeptide Y), and prevents ethanol, known otherwise as rewarding to flies [6, 7], from being rewarding [5]. It is not clear which of the multiple sensory and motor responses performed during mating induces perception of reward. Sexual interactions with female flies that do not reach copulation are not sufficient to reduce ethanol consumption [5], suggesting that only successful mating encounters are rewarding. Here, we uncoupled the initial steps of mating from its final steps and tested the ability of ejaculation to mimic the rewarding value of full copulation. We induced ejaculation by activating neurons that express the neuropeptide corazonin (CRZ) [8] and subsequently measured different aspects of reward. We show that activating Crz-expressing neurons is rewarding to male flies, as they choose to reside in a zone that triggers optogenetic stimulation of Crz neurons and display conditioned preference for an odor paired with the activation. Reminiscent of successful mating, repeated activation of Crz neurons increases npf levels and reduces ethanol consumption. Our results demonstrate that ejaculation stimulated by Crz/Crz-receptor signaling serves as an essential part of the mating reward mechanism in Drosophila. Video
      Graphical abstract image Teaser Zer-Krispil et al. report that ejaculation induced by the activation of male-specific Crz neurons is sufficient to mimic all the rewarding aspects of successful copulation in Drosophila. The activation carries positive valence, induces npf transcript levels, drives appetitive memories, and reduces the motivation to consume ethanol as a drug reward.

      PubDate: 2018-05-17T08:29:41Z
       
  • A Visual Cortical Network for Deriving Phonological Information from
           Intelligible Lip Movements
    • Abstract: Publication date: 7 May 2018
      Source:Current Biology, Volume 28, Issue 9
      Author(s): Anne Hauswald, Chrysa Lithari, Olivier Collignon, Elisa Leonardelli, Nathan Weisz
      Successful lip-reading requires a mapping from visual to phonological information [1]. Recently, visual and motor cortices have been implicated in tracking lip movements (e.g., [2]). It remains unclear, however, whether visuo-phonological mapping occurs already at the level of the visual cortex–that is, whether this structure tracks the acoustic signal in a functionally relevant manner. To elucidate this, we investigated how the cortex tracks (i.e., entrains to) absent acoustic speech signals carried by silent lip movements. Crucially, we contrasted the entrainment to unheard forward (intelligible) and backward (unintelligible) acoustic speech. We observed that the visual cortex exhibited stronger entrainment to the unheard forward acoustic speech envelope compared to the unheard backward acoustic speech envelope. Supporting the notion of a visuo-phonological mapping process, this forward-backward difference of occipital entrainment was not present for actually observed lip movements. Importantly, the respective occipital region received more top-down input, especially from left premotor, primary motor, and somatosensory regions and, to a lesser extent, also from posterior temporal cortex. Strikingly, across participants, the extent of top-down modulation of the visual cortex stemming from these regions partially correlated with the strength of entrainment to absent acoustic forward speech envelope, but not to present forward lip movements. Our findings demonstrate that a distributed cortical network, including key dorsal stream auditory regions [3–5], influences how the visual cortex shows sensitivity to the intelligibility of speech while tracking silent lip movements.
      Teaser Successful lip-reading requires a visual-phonological transformation. Hauswald et al. show that, during the processing of silently played lip movements, the visual cortex tracks the missing acoustic speech information when played forward as compared to backward. The effect is under top-down control.

      PubDate: 2018-05-17T08:29:41Z
       
  • Animals Remember Previous Facial Expressions that Specific Humans Have
           Exhibited
    • Authors: Leanne Proops; Kate Grounds; Amy Victoria Smith; Karen McComb
      Abstract: Publication date: Available online 26 April 2018
      Source:Current Biology
      Author(s): Leanne Proops, Kate Grounds, Amy Victoria Smith, Karen McComb
      For humans, facial expressions are important social signals, and how we perceive specific individuals may be influenced by subtle emotional cues that they have given us in past encounters. A wide range of animal species are also capable of discriminating the emotions of others through facial expressions [1–5], and it is clear that remembering emotional experiences with specific individuals could have clear benefits for social bonding and aggression avoidance when these individuals are encountered again. Although there is evidence that non-human animals are capable of remembering the identity of individuals who have directly harmed them [6, 7], it is not known whether animals can form lasting memories of specific individuals simply by observing subtle emotional expressions that they exhibit on their faces. Here we conducted controlled experiments in which domestic horses were presented with a photograph of an angry or happy human face and several hours later saw the person who had given the expression in a neutral state. Short-term exposure to the facial expression was enough to generate clear differences in subsequent responses to that individual (but not to a different mismatched person), consistent with the past angry expression having been perceived negatively and the happy expression positively. Both humans were blind to the photograph that the horses had seen. Our results provide clear evidence that some non-human animals can effectively eavesdrop on the emotional state cues that humans reveal on a moment-to-moment basis, using their memory of these to guide future interactions with particular individuals.
      Teaser Proops et al. show that, like humans, horses remember past expressions seen on the faces of particular people and use this emotional memory to guide future interactions. Their response is more negative if they previously saw an angry versus a happy photo of the person, and this memory is specific to the person whose face they saw.

      PubDate: 2018-04-26T19:16:00Z
      DOI: 10.1016/j.cub.2018.03.035
       
  • The Geomagnetic Field Is a Compass Cue in Cataglyphis Ant Navigation
    • Authors: Pauline Nikola Fleischmann; Robin Grob; Valentin Leander Müller; Rüdiger Wehner; Wolfgang Rössler
      Abstract: Publication date: Available online 26 April 2018
      Source:Current Biology
      Author(s): Pauline Nikola Fleischmann, Robin Grob, Valentin Leander Müller, Rüdiger Wehner, Wolfgang Rössler
      Desert ants (Cataglyphis) are famous insect navigators. During their foraging lives, the ants leave their underground colonies for long distances and return to their starting point with fair accuracy [1, 2]. Their incessantly running path integrator provides them with a continually updated home vector [3–5]. Directional input to their path integrator is provided by a visual compass based on celestial cues [6, 7]. However, as path integration is prone to cumulative errors, the ants additionally employ landmark guidance routines [8–11]. At the start of their foraging lives, they acquire the necessary landmark information by performing well-structured learning walks [12, 13], including turns about their vertical body axes [14]. When Cataglyphis noda performs these pirouettes, it always gazes at the nest entrance during the longest of several short stopping phases [14]. As the small nest entrance is not visible, the ants can adjust their gaze direction only by reading out their path integrator. However, recent experiments have shown that, for adjusting the goal-centered gaze directions during learning walks, skylight cues are not required [15]. A most promising remaining compass cue is the geomagnetic field, which is used for orientation in one way or the other by a variety of animal species [16–25]. Here, we show that the gaze directions during the look-back-to-the-nest behavior change in a predictable way to alterations of the horizontal component of the magnetic field. This is the first demonstration that, in insects, a geomagnetic compass cue is both necessary and sufficient for accomplishing a well-defined navigational task.
      Graphical abstract image Teaser Cataglyphis ant novices perform learning walks to acquire all information that is necessary for successful navigation as foragers later on. For that reason, they take snapshots of the nest’s surrounding during pirouettes. Fleischmann et al. show that the geomagnetic field is necessary and sufficient for aligning the gazes to the invisible nest entrance.

      PubDate: 2018-04-26T19:16:00Z
      DOI: 10.1016/j.cub.2018.03.043
       
  • Coin Tossing Explains the Activity of Opposing Microtubule Motors on
           Phagosomes
    • Authors: Paulomi Sanghavi; Ashwin D’Souza; Ashim Rai; Arpan Rai; Ranjith Padinhatheeri; Roop Mallik
      Abstract: Publication date: Available online 26 April 2018
      Source:Current Biology
      Author(s): Paulomi Sanghavi, Ashwin D’Souza, Ashim Rai, Arpan Rai, Ranjith Padinhatheeri, Roop Mallik
      How the opposing activity of kinesin and dynein motors generates polarized distribution of organelles inside cells is poorly understood and hotly debated [1, 2]. Possible explanations include stochastic mechanical competition [3, 4], coordinated regulation by motor-associated proteins [5–7], mechanical activation of motors [8], and lipid-induced organization [9]. Here, we address this question by using phagocytosed latex beads to generate early phagosomes (EPs) that move bidirectionally along microtubules (MTs) in an in vitro assay [9]. Dynein/kinesin activity on individual EPs is recorded as real-time force generation of the motors against an optical trap. Activity of one class of motors frequently coincides with, or is rapidly followed by opposite motors. This leads to frequent and rapid reversals of EPs in the trap. Remarkably, the choice between dynein and kinesin can be explained by the tossing of a coin. Opposing motors therefore appear to function stochastically and independently of each other, as also confirmed by observing no effect on kinesin function when dynein is inhibited on the EPs. A simple binomial probability calculation based on the geometry of EP-microtubule contact explains the observed activity of dynein and kinesin on phagosomes. This understanding of intracellular transport in terms of a hypothetical coin, if it holds true for other cargoes, provides a conceptual framework to explain the polarized localization of organelles inside cells.
      Teaser Sanghavi et al. analyze optical trapping data on phagosomes to propose that sub-cellular localization of organelles inside cells can be understood in terms of a hypothetical coin toss that decides motor protein activity (dynein versus kinesin) on the phagosome.

      PubDate: 2018-04-26T19:16:00Z
      DOI: 10.1016/j.cub.2018.03.041
       
  • Chromosome Segregation Is Biased by Kinetochore Size
    • Authors: Danica Drpic; Ana Almeida Paulo Aguiar Fioranna Renda Joana Damas
      Abstract: Publication date: Available online 26 April 2018
      Source:Current Biology
      Author(s): Danica Drpic, Ana C. Almeida, Paulo Aguiar, Fioranna Renda, Joana Damas, Harris A. Lewin, Denis M. Larkin, Alexey Khodjakov, Helder Maiato
      Chromosome missegregation during mitosis or meiosis is a hallmark of cancer and the main cause of prenatal death in humans. The gain or loss of specific chromosomes is thought to be random, with cell viability being essentially determined by selection. Several established pathways including centrosome amplification, sister-chromatid cohesion defects, or a compromised spindle assembly checkpoint can lead to chromosome missegregation. However, how specific intrinsic features of the kinetochore—the critical chromosomal interface with spindle microtubules—impact chromosome segregation remains poorly understood. Here we used the unique cytological attributes of female Indian muntjac, the mammal with the lowest known chromosome number (2n = 6), to characterize and track individual chromosomes with distinct kinetochore size throughout mitosis. We show that centromere and kinetochore functional layers scale proportionally with centromere size. Measurement of intra-kinetochore distances, serial-section electron microscopy, and RNAi against key kinetochore proteins confirmed a standard structural and functional organization of the Indian muntjac kinetochores and revealed that microtubule binding capacity scales with kinetochore size. Surprisingly, we found that chromosome segregation in this species is not random. Chromosomes with larger kinetochores bi-oriented more efficiently and showed a 2-fold bias to congress to the equator in a motor-independent manner. Despite robust correction mechanisms during unperturbed mitosis, chromosomes with larger kinetochores were also strongly biased to establish erroneous merotelic attachments and missegregate during anaphase. This bias was impervious to the experimental attenuation of polar ejection forces on chromosome arms by RNAi against the chromokinesin Kif4a. Thus, kinetochore size is an important determinant of chromosome segregation fidelity.
      Graphical abstract image Teaser Drpic et al. use fibroblasts from female Indian muntjac, the mammal with the lowest known chromosome number (2n = 6), to show that chromosome congression and bi-orientation are biased by kinetochore size. Chromosomes with larger kinetochores are also biased to establish erroneous merotelic attachments and missegregate during anaphase. Thus, kinetochore size is an important determinant of chromosome segregation fidelity.

      PubDate: 2018-04-26T19:16:00Z
       
  • Coordination of Septate Junctions Assembly and Completion of Cytokinesis
           in Proliferative Epithelial Tissues
    • Authors: Emeline Daniel; Marion Daudé; Irina Kolotuev; Kristi Charish; Vanessa Auld; Roland Le Borgne
      Abstract: Publication date: Available online 26 April 2018
      Source:Current Biology
      Author(s): Emeline Daniel, Marion Daudé, Irina Kolotuev, Kristi Charish, Vanessa Auld, Roland Le Borgne
      How permeability barrier function is maintained when epithelial cells divide is largely unknown. Here, we have investigated how the bicellular septate junctions (BSJs) and tricellular septate junctions (TSJs) are remodeled throughout completion of cytokinesis in Drosophila epithelia. We report that, following cytokinetic ring constriction, the midbody assembles, matures within SJs, and is displaced basally in two phases. In a first slow phase, the neighboring cells remain connected to the dividing cells by means of SJ-containing membrane protrusions pointing to the maturing midbody. Fluorescence recovery after photobleaching (FRAP) experiments revealed that SJs within the membrane protrusions correspond to the old SJs that were present prior to cytokinesis. In contrast, new SJs are assembled below the adherens junctions and spread basally to build a new belt of SJs in a manner analogous to a conveyor belt. Loss of function of a core BSJ component, the Na+/K+-ATPase pump Nervana 2 subunit, revealed that the apical-to-basal spread of BSJs drives the basal displacement of the midbody. In contrast, loss of the TSJ protein Bark beetle indicated that remodeling of TSJs is rate limiting and slowed down midbody migration. In the second phase, once the belt of SJs is assembled, the basal displacement of the midbody is accelerated and ultimately leads to abscission. This last step is temporally uncoupled from the remodeling of SJs. We propose that cytokinesis in epithelia involves the coordinated polarized assembly and remodeling of SJs both in the dividing cell and its neighbors to ensure the maintenance of permeability barrier integrity in proliferative epithelia.
      Teaser Using live imaging and electron microscopy of Drosophila epithelia, Daniel et al. investigate how septate junctions are remodeled during cytokinesis and show that it is a multicellular process relying on the interplay between dividing cells and their neighbors, thereby ensuring the maintenance of permeability barrier function.

      PubDate: 2018-04-26T19:16:00Z
      DOI: 10.1016/j.cub.2018.03.034
       
  • Puncture-and-Pull Biomechanics in the Teeth of Predatory Coelurosaurian
           Dinosaurs
    • Authors: Angelica Torices; Ryan Wilkinson; Victoria M. Arbour; Jose Ignacio Ruiz-Omeñaca; Philip J. Currie
      Abstract: Publication date: Available online 26 April 2018
      Source:Current Biology
      Author(s): Angelica Torices, Ryan Wilkinson, Victoria M. Arbour, Jose Ignacio Ruiz-Omeñaca, Philip J. Currie
      The teeth of putatively carnivorous dinosaurs are often blade-shaped with well-defined serrated cutting edges (Figure 1). These ziphodont teeth are often easily differentiated based on the morphology and density of the denticles [1, 2]. A tearing function has been proposed for theropod denticles in general [3], but the functional significance of denticle phenotypic variation has received less attention. In particular, the unusual hooked denticles found in troodontids suggest a different feeding strategy or diet compared to other small theropods. We used a two-pronged approach to investigate the function of denticle shape variation across theropods with both congruent body shapes and sizes (e.g., dromaeosaurids versus troodontids) and highly disparate body shapes and sizes (e.g., troodontids versus tyrannosaurids), using microwear and finite element analyses (Figure 1). We found that many toothed coelurosaurian theropods employed a puncture-and-pull feeding movement, in which parallel scratches form while biting down into prey and oblique scratches form as the head is pulled backward with the jaws closed. In finite element simulations, theropod teeth had the lowest stresses when bite forces were aligned with the oblique family of microwear scratches. Different denticle morphologies performed differently under a variety of simulated biting angles: Dromaeosaurus and Saurornitholestes were well-adapted for handling struggling prey, whereas troodontid teeth were more likely to fail at non-optimal bite angles. Troodontids may have favored softer, smaller, or immobile prey.
      Teaser Torices et al. use tooth microwear to show that theropod dinosaurs with differing bauplans used similar feeding movements for dismembering prey. Finite element analyses further reveal that troodontid teeth were more likely to fail at non-optimal bite angles and may have had a markedly different diet than their close dromaeosaurid relatives.

      PubDate: 2018-04-26T19:16:00Z
      DOI: 10.1016/j.cub.2018.03.042
       
 
 
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