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Journal Cover Current Biology
  [SJR: 4.729]   [H-I: 258]   [225 followers]  Follow
    
   Full-text available via subscription Subscription journal
   ISSN (Print) 0960-9822
   Published by Elsevier Homepage  [3089 journals]
  • Vagus Motor Neuron Topographic Map Determined by Parallel Mechanisms of
           hox5 Expression and Time of Axon Initiation
    • Abstract: Publication date: Available online 7 December 2017
      Source:Current Biology
      Author(s): Gabrielle R. Barsh, Adam J. Isabella, Cecilia B. Moens
      Many networks throughout the nervous system are organized into topographic maps, where the positions of neuron cell bodies in the projecting field correspond with the positions of their axons in the target field. Previous studies of topographic map development show evidence for spatial patterning mechanisms, in which molecular determinants expressed across the projecting and target fields are matched directly in a point-to-point mapping process. Here, we describe a novel temporal mechanism of topographic map formation that depends on spatially regulated differences in the timing of axon outgrowth and functions in parallel with spatial point-to-point mapping mechanisms. We focus on the vagus motor neurons, which are topographically arranged in both mammals and fish. We show that cell position along the anterior-posterior axis of hindbrain rhombomere 8 determines expression of hox5 genes, which are expressed in posterior, but not anterior, vagus motor neurons. Using live imaging and transplantation in zebrafish embryos, we additionally reveal that axon initiation is delayed in posterior vagus motor neurons independent of neuron birth time. We show that hox5 expression directs topographic mapping without affecting time of axon outgrowth and that time of axon outgrowth directs topographic mapping without affecting hox5 expression. The vagus motor neuron topographic map is therefore determined by two mechanisms that act in parallel: a hox5-dependent spatial mechanism akin to classic mechanisms of topographic map formation and a novel axon outgrowth-dependent temporal mechanism in which time of axon formation is spatially regulated to direct axon targeting.
      Teaser The development of topographic maps classically relies upon spatial patterning mechanisms. Barsh et al. show that in zebrafish vagus motor neurons, map formation is determined by a hox5-dependent spatial mechanism that acts in parallel with a novel temporal mechanism dependent upon the time of axon outgrowth.

      PubDate: 2017-12-08T14:56:14Z
       
  • Differential Effects of Climate on Survival Rates Drive Hybrid Zone
           Movement
    • Abstract: Publication date: Available online 7 December 2017
      Source:Current Biology
      Author(s): Elizabeth A. Hunter, Marjorie D. Matocq, Peter J. Murphy, Kevin T. Shoemaker
      Climate change has been implicated as driving shifts of hybridizing species’ range limits [1, 2]. Whether and how much hybrid zones move depends on the relative fitness of hybridzing species under changing conditions [3, 4]. However, fitness is rarely linked to both climatic conditions and movement of hybrid zones, such that the relationship between climate change and hybrid zone dynamics remains tenuous [5]. Here we report how interactions between climate (seasonal precipitation) and competitor densities result in steep differentials in survival, which in turn drive hybrid zone movement for two woodrat species (Neotoma fuscipes and N. macrotis) in central California, USA. Using 6 years of capture-mark-recapture data, we found that the smaller-bodied species, N. macrotis, and hybrids had survival advantages over the larger-bodied N. fuscipes in the contact region during dry winters and wet springs. This pattern of differential survival, with N. macrotis having a consistent advantage over N. fuscipes during our study period, matched the spatial dynamics of the hybrid zone, which moved steadily north into N. fuscipes territory, with its estimated center moving ∼150 m north in 6 years. Our findings provide a unique demonstration of range movements emerging from a complex interplay between climate and competition. Although all study site areas experienced the same climatic conditions, competitive effects created a complex spatial pattern of survival differentials, which in turn influenced hybrid zone movement. Characterization of fitness differentials derived from replicated demographic studies of contact regions between competitors should greatly improve our ability to understand and forecast climate-driven range dynamics.
      Teaser Hunter et al. show that climate- and competition-driven survival differentials in two species of hybridizing Neotoma woodrats correspond to a northward movement of the hybrid zone. These results demonstrate the importance of delineating competing species’ fitness differentials to predict how range limits will shift under a changing climate.

      PubDate: 2017-12-08T14:56:14Z
       
  • The Mitotic Function of Augmin Is Dependent on Its Microtubule-Associated
           Protein Subunit EDE1 in Arabidopsis thaliana
    • Abstract: Publication date: Available online 7 December 2017
      Source:Current Biology
      Author(s): Yuh-Ru Julie Lee, Yuji Hiwatashi, Takashi Hotta, Tingting Xie, John H. Doonan, Bo Liu
      The augmin complex plays an essential role in microtubule (MT)-dependent MT nucleation by recruiting the γ-tubulin complex to MT walls to generate new MTs [1]. The complex contains eight subunits (designated AUG) including AUG8, which is an MT-associated protein (MAP). When this complex is isolated from etiolated seedlings consisting of primarily interphase cells in Arabidopsis thaliana, AUG8 is an integral component [2]. EDE1 (Endosperm DEfective 1) is homologous to AUG8 [3]. Here, we demonstrate that EDE1, but not AUG8, is associated with acentrosomal spindle and phragmoplast MT arrays in patterns indistinguishable from those of the AUG1–7 subunits and the γ-tubulin complex proteins (GCPs) that exhibit biased localization toward MT minus ends. Consistent with this colocalization, EDE1 directly interacts with AUG6 in vivo. Moreover, a partial loss-of-function mutation, ede1-1, compromises the localization of augmin and γ-tubulin on the spindle and phragmoplast MT arrays and leads to serious distortions in spindle MT remodeling during mitosis. However, mitosis continues even when kinetochore fibers are not obviously discernable, and cytokinesis takes place following the formation of elongated bipolar phragmoplast MT arrays in the mutant. Hence, we conclude that the mitotic function of augmin is dependent on its MAP subunit EDE1, which cannot be replaced by AUG8, and that the cell-cycle-dependent function of augmin can be differentially regulated by employing distinct MAP subunits. Our results also illustrate that plant cells can respond flexibly to serious challenges of compromised MT-dependent MT nucleation to complete mitosis and cytokinesis.
      Graphical abstract image Teaser Augmin activates MT-dependent MT nucleation in both interphase and mitotic cells in plants. It has been unclear how the augmin function is differentially regulated under the two circumstances. Lee et al. demonstrate that a member of the AUG8 MT-associated protein family, EDE1, specifies the mitotic function of augmin in Arabidopsis.

      PubDate: 2017-12-08T14:56:14Z
       
  • Origins and Specification of the Drosophila Wing
    • Abstract: Publication date: Available online 7 December 2017
      Source:Current Biology
      Author(s): David Requena, Jose Andres Álvarez, Hugo Gabilondo, Ryan Loker, Richard S. Mann, Carlos Estella
      The insect wing is a key evolutionary innovation that was essential for insect diversification. Yet despite its importance, there is still debate about its evolutionary origins. Two main hypotheses have been proposed: the paranotal hypothesis, which suggests that wings evolved as an extension of the dorsal thorax, and the gill-exite hypothesis, which proposes that wings were derived from a modification of a pre-existing branch at the dorsal base (subcoxa) of the leg. Here, we address this question by studying how wing fates are initially specified during Drosophila embryogenesis, by characterizing a cis-regulatory module (CRM) from the snail (sna) gene, sna-DP (for dorsal primordia). sna-DP specifically marks the early primordia for both the wing and haltere, collectively referred to as the DP. We found that the inputs that activate sna-DP are distinct from those that activate Distalless, a marker for leg fates. Further, in genetic backgrounds in which the leg primordia are absent, the DP are still partially specified. However, lineage-tracing experiments demonstrate that cells from the early leg primordia contribute to both ventral and dorsal appendage fates. Together, these results suggest that the wings of Drosophila have a dual developmental origin: two groups of cells, one ventral and one more dorsal, give rise to the mature wing. We suggest that the dual developmental origins of the wing may be a molecular remnant of the evolutionary history of this appendage, in which cells of the subcoxa of the leg coalesced with dorsal outgrowths to evolve a dorsal appendage with motor control.
      Graphical abstract image Teaser By studying a cis-regulatory module that is specifically active in the embryonic dorsal (wing and haltere) primordia of Drosophila, Requena et al. demonstrate that dorsal fates are derived from two separate groups of cells, one of which shares a lineage with the ventral primordia. These data are consistent with a dual evolutionary origin of the wing.

      PubDate: 2017-12-08T14:56:14Z
       
  • Evolution of the Sauropterygian Labyrinth with Increasingly Pelagic
           Lifestyles
    • Abstract: Publication date: Available online 7 December 2017
      Source:Current Biology
      Author(s): James M. Neenan, Tobias Reich, Serjoscha W. Evers, Patrick S. Druckenmiller, Dennis F.A.E. Voeten, Jonah N. Choiniere, Paul M. Barrett, Stephanie E. Pierce, Roger B.J. Benson
      Sauropterygia, a successful clade of marine reptiles abundant in aquatic ecosystems of the Mesozoic, inhabited nearshore to pelagic habitats over >180 million years of evolutionary history [1]. Aquatic vertebrates experience strong buoyancy forces that allow movement in a three-dimensional environment, resulting in structural convergences such as flippers and fish-like bauplans [2, 3], as well as convergences in the sensory systems. We used computed tomographic scans of 19 sauropterygian species to determine how the transition to pelagic lifestyles influenced the evolution of the endosseous labyrinth, which houses the vestibular sensory organ of balance and orientation [4]. Semicircular canal geometries underwent distinct changes during the transition from nearshore Triassic sauropterygians to the later, pelagic plesiosaurs. Triassic sauropterygians have dorsoventrally compact, anteroposteriorly elongate labyrinths, resembling those of crocodylians. In contrast, plesiosaurs have compact, bulbous labyrinths, sharing some features with those of sea turtles. Differences in relative labyrinth size among sauropterygians correspond to locomotory differences: bottom-walking [5, 6] placodonts have proportionally larger labyrinths than actively swimming taxa (i.e., all other sauropterygians). Furthermore, independent evolutionary origins of short-necked, large-headed “pliosauromorph” body proportions among plesiosaurs coincide with reductions of labyrinth size, paralleling the evolutionary history of cetaceans [7]. Sauropterygian labyrinth evolution is therefore correlated closely with both locomotory style and body proportions, and these changes are consistent with isolated observations made previously in other marine tetrapods. Our study presents the first virtual reconstructions of plesiosaur endosseous labyrinths and the first large-scale, quantitative study detailing the effects of increasingly aquatic lifestyles on labyrinth morphology among marine reptiles.
      Teaser Neenan et al. quantify endosseous labyrinth shape across a group of extinct marine reptiles called Sauropterygia. They find distinctly different labyrinth proportions depending on locomotory mode. Importantly, independent radiations of short-necked plesiosaurs with whale-like body proportions have miniaturized labyrinths, much like extant cetaceans.

      PubDate: 2017-12-08T14:56:14Z
       
  • At Birth, Humans Associate “Few” with Left and
           “Many” with Right
    • Abstract: Publication date: Available online 7 December 2017
      Source:Current Biology
      Author(s): Maria Dolores de Hevia, Ludovica Veggiotti, Arlette Streri, Cory D. Bonn
      Humans use spatial representations to structure abstract concepts [1]. One of the most well-known examples is the “mental number line”—the propensity to imagine numbers oriented in space [2, 3]. Human infants [4, 5], children [6, 7], adults [8], and nonhuman animals [9, 10] associate small numbers with the left side of space and large numbers with the right. In humans, cultural artifacts, such as the direction of reading and writing, modulate the directionality of this representation, with right-to-left reading cultures associating small numbers with right and large numbers with left [11], whereas the opposite association permeates left-to-right reading cultures [8]. Number-space mapping plays a central role in human mathematical concepts [12], but its origins remain unclear: is it the result of an innate bias or does it develop after birth' Infant humans are passively exposed to a spatially coded environment, so experience and culture could underlie the mental number line. To rule out this possibility, we tested neonates’ responses to small or large auditory quantities paired with geometric figures presented on either the left or right sides of the screen. We show that 0- to 3-day-old neonates associate a small quantity with the left and a large quantity with the right when the multidimensional stimulus contains discrete numerical information, providing evidence that representations of number are associated to an oriented space at the start of postnatal life, prior to experience with language, culture, or with culture-specific biases.
      Teaser de Hevia et al. show in a series of five experiments that newborns possess a left-few/right-many bias. The results suggest that the predisposition to map numbers to spatial locations is independent of postnatal sensory experience.

      PubDate: 2017-12-08T14:56:14Z
       
  • Causes and Consequences of Tool Shape Variation in New Caledonian Crows
    • Abstract: Publication date: Available online 7 December 2017
      Source:Current Biology
      Author(s): Shoko Sugasawa, Barbara C. Klump, James J.H. St Clair, Christian Rutz
      Hominins have been making tools for over three million years [1], yet the earliest known hooked tools appeared as recently as 90,000 years ago [2]. Hook innovation is likely to have boosted our ancestors’ hunting and fishing efficiency [3], marking a major transition in human technological evolution. The New Caledonian crow is the only non-human animal known to craft hooks in the wild [4, 5]. Crows manufacture hooked stick tools in a multi-stage process, involving the detachment of a branch from suitable vegetation; “sculpting” of a terminal hook from the nodal joint; and often additional adjustments, such as length trimming, shaft bending, and bark stripping [4, 6, 7]. Although tools made by a given population share key design features [4, 6, 8], they vary appreciably in overall shape and hook dimensions. Using wild-caught, temporarily captive crows, we experimentally investigated causes and consequences of variation in hook-tool morphology. We found that bird age, manufacture method, and raw-material properties influenced tool morphology, and that hook geometry in turn affected crows’ foraging efficiency. Specifically, hook depth varied with both detachment technique and plant rigidity, and deeper hooks enabled faster prey extraction in the provided tasks. Older crows manufactured tools of distinctive shape, with pronounced shaft curvature and hooks of intermediate depth. Future work should explore the interactive effects of extrinsic and intrinsic factors on tool production and deployment. Our study provides a quantitative assessment of the drivers and functional significance of tool shape variation in a non-human animal, affording valuable comparative insights into early hominin tool crafting [9].
      Teaser The New Caledonian crow is the only non-human animal known to craft hooked foraging tools. In experiments with wild-caught crows, Sugasawa et al. identify extrinsic and intrinsic factors that affect tool morphology and, as a consequence, tool efficiency. This provides valuable insights into the drivers and constraints of technological evolution.

      PubDate: 2017-12-08T14:56:14Z
       
  • Neuropeptide Y Regulates Sleep by Modulating Noradrenergic Signaling
    • Abstract: Publication date: Available online 7 December 2017
      Source:Current Biology
      Author(s): Chanpreet Singh, Jason Rihel, David A. Prober
      Sleep is an essential and evolutionarily conserved behavioral state whose regulation remains poorly understood. To identify genes that regulate vertebrate sleep, we recently performed a genetic screen in zebrafish, and here we report the identification of neuropeptide Y (NPY) as both necessary for normal daytime sleep duration and sufficient to promote sleep. We show that overexpression of NPY increases sleep, whereas mutation of npy or ablation of npy-expressing neurons decreases sleep. By analyzing sleep architecture, we show that NPY regulates sleep primarily by modulating the length of wake bouts. To determine how NPY regulates sleep, we tested for interactions with several systems known to regulate sleep, and provide anatomical, molecular, genetic, and pharmacological evidence that NPY promotes sleep by inhibiting noradrenergic signaling. These data establish NPY as an important vertebrate sleep/wake regulator and link NPY signaling to an established arousal-promoting system.
      Teaser Based on a genetic screen, Singh et al. identify NPY signaling and npy-expressing neurons as regulators of zebrafish sleep. They show that NPY promotes sleep by inhibiting noradrenergic signaling, thus linking NPY signaling to an established arousal-promoting system.

      PubDate: 2017-12-08T14:56:14Z
       
  • Tension-Dependent Stretching Activates ZO-1 to Control the Junctional
           Localization of Its Interactors
    • Abstract: Publication date: Available online 5 December 2017
      Source:Current Biology
      Author(s): Domenica Spadaro, Shimin Le, Thierry Laroche, Isabelle Mean, Lionel Jond, Jie Yan, Sandra Citi
      Tensile forces regulate epithelial homeostasis, but the molecular mechanisms behind this regulation are poorly understood. Using structured illumination microscopy and proximity ligation assays, we show that the tight junction protein ZO-1 exists in stretched and folded conformations within epithelial cells, depending on actomyosin-generated force. We also show that ZO-1 and ZO-2 regulate the localization of the transcription factor DbpA and the tight junction membrane protein occludin in a manner that depends on the organization of the actin cytoskeleton, myosin-II activity, and substrate stiffness, resulting in modulation of gene expression, cell proliferation, barrier function, and cyst morphogenesis. Pull-down experiments show that interactions between N-terminal (ZPSG) and C-terminal domains of ZO-1 prevent binding of DbpA to the ZPSG, suggesting that force-dependent intra-molecular interactions regulate ZPSG binding to ligands within cells. In vivo and in vitro experiments also suggest that ZO-1 heterodimerization with ZO-2 promotes the stretched conformation and ZPSG interaction with ligands. Magnetic tweezers single-molecule experiments suggest that pN-scale tensions (∼2–4 pN) are sufficient to maintain the stretched conformation of ZO-1, while keeping its structured domains intact, and that 5–20 pN force is required to disrupt the interaction between the extreme C-terminal and the ZPSG domains of ZO-1. We propose that tensile forces regulate epithelial homeostasis by activating ZO proteins through stretching, to control the junctional recruitment and downstream signaling of their interactors.
      Graphical abstract image Teaser Spadaro et al. use super-resolution microscopy to show that ZO-1, a protein that connects tight junction membrane proteins to the actin cytoskeleton, exists in either stretched or folded conformations, depending on actomyosin-dependent force, resulting in changes in the localization, stability, and downstream signaling of its interactors.

      PubDate: 2017-12-08T14:56:14Z
       
  • Finding good explanations for bad weather
    • Abstract: Publication date: 4 December 2017
      Source:Current Biology, Volume 27, Issue 23
      Author(s): Michael Gross
      Two years after the Paris climate conference, the world isn’t all that much closer to achieving the 2°C goal agreed there. The science of analysing the connection between extreme weather events and climate change, however, has made significant progress. At least in the case of simple, large-scale events like heat waves, simulations can now attribute fractional blame to emitting countries. Michael Gross reports.
      Teaser “Two years after the Paris climate conference, the world isn’t all that much closer to achieving the agreed goals. The science of analysing the connection between extreme weather events and climate change, however, has made significant progress. For simple, large-scale events like heat waves, simulations can now attribute fractional blame to emitting countries.”

      PubDate: 2017-12-08T14:56:14Z
       
  • Britt Koskella
    • Abstract: Publication date: 4 December 2017
      Source:Current Biology, Volume 27, Issue 23
      Author(s): Britt Koskella
      Teaser Interview with Britt Koskella, assistant professor in the Department of Integrative Biology at University of California, Berkeley.

      PubDate: 2017-12-08T14:56:14Z
       
  • Sampling Darwin
    • Abstract: Publication date: 4 December 2017
      Source:Current Biology, Volume 27, Issue 23
      Author(s): Andrew Berry


      PubDate: 2017-12-08T14:56:14Z
       
  • PARPs
    • Abstract: Publication date: 4 December 2017
      Source:Current Biology, Volume 27, Issue 23
      Author(s): Anthony K.L. Leung
      Teaser Leung introduces the various roles of PARPs and the regulation of ADP-ribosylation of protein substrates.

      PubDate: 2017-12-08T14:56:14Z
       
  • Transcranial electrical stimulation
    • Abstract: Publication date: 4 December 2017
      Source:Current Biology, Volume 27, Issue 23
      Author(s): Sven Bestmann, Vincent Walsh
      Transcranial electrical stimulation (tES) is a neuromodulatory technique in which low voltage constant or alternating currents are applied to the human brain via scalp electrodes. The basic idea of tES is that the application of weak currents can interact with neural processing, modify plasticity and entrain brain networks, and that this in turn can modify behaviour. The technique is now widely employed in basic and translational research, and increasingly is also used privately in sport, the military and recreation. The proposed capacity to augment recovery of brain function, by promoting learning and facilitating plasticity, has motivated a burgeoning number of clinical trials in a wide range of disorders of the nervous system.
      Teaser A Primer by Bestmann and Walsh explaining how weak transcranial electric currents affect the human brain, with a critical look at concepts, mechanisms, and future directions.

      PubDate: 2017-12-08T14:56:14Z
       
  • Ocean sunfish as indicators for the ‘rise of slime’
    • Abstract: Publication date: 4 December 2017
      Source:Current Biology, Volume 27, Issue 23
      Author(s): David Grémillet, Craig R. White, Matthieu Authier, Ghislain Dorémus, Vincent Ridoux, Emeline Pettex
      Overfishing and ocean warming are drastically altering the community composition and size structure of marine ecosystems, eliminating large bodied species [1]. Against a backdrop of such environmental change, the heaviest of all bony fish, the ocean sunfish (Mola mola), seems an improbable survivor. Indeed this indolent giant is killed globally as bycatch, and is listed as ‘Vulnerable’ [2]. We undertook the most extensive aerial surveys of sunfish ever conducted and found surprisingly high abundances off the Atlantic and Mediterranean coasts of Western Europe. With up to 475 individuals per 100 km2, these figures are one order of magnitude higher than abundance estimates for other areas [3–5]. Using bioenergetic modelling, we estimate that each sunfish requires 71 kg day–1 of jellyfish, a biomass intake more than an order of magnitude greater than predicted for a similarly sized teleost. Scaled up to the population level, this equates to a remarkable 20,774 tonnes day–1 of predated jellyfish across our study area in summer. Sunfish abundance may be facilitated by overfishing and ocean warming, which together cause reduced predation of sunfish by sharks and elevated jellyfish biomass. Our combined survey and bioenergetic data provide the first-ever estimate of spatialized ocean sunfish daily food requirements, and stress the importance of this species as a global indicator for the ‘rise of slime’. This hypothesis posits that, in an overfished world ocean exposed to global warming, gelatinous zooplankton should flourish, to the detriment of other mesotrophic species such as small pelagic fish, causing irreversible trophic cascades as well as a series of other environmental and economic issues.
      Teaser The Ocean Sunfish is the heaviest of all bony fish, and is listed as vulnerable by the IUCN. Grémillet et al. conducted aerial surveys off the Atlantic and Mediterranean coasts of Western Europe, finding up to 475 sunfish per 100 km2. The sunfish population in this region is estimated to consume over 20,000 tonnes of jellyfish per day in summer.

      PubDate: 2017-12-08T14:56:14Z
       
  • Non-cortical magnitude coding of space and time by pigeons
    • Abstract: Publication date: 4 December 2017
      Source:Current Biology, Volume 27, Issue 23
      Author(s): Benjamin J. De Corte, Victor M. Navarro, Edward A. Wasserman
      Considerable research in cognitive science, neuroscience, and developmental science has revealed that the temporal, spatial, and numerical features of a stimulus can interact with one another [1,2], as when larger stimuli are perceived as lasting longer than smaller stimuli. These findings have inspired the prominent hypothesis that time, space, and number are processed by a ‘common magnitude system’, which represents these dimensions via the same unit of magnitude [3,4]. According to current theorizing, the parietal cortex mediates this system [4]. To test the species generality and neuroanatomical foundations of this hypothesis, we asked whether space–time interactions can be observed in birds. Unlike mammals, birds lack a cortex [5,6]; rather, they possess a neuron-dense pallium that is organized in clusters, in contrast to the laminar structure of the mammalian cortex [7]. Despite these striking neuroanatomical disparities, we observed reliable space–time interactions in pigeons. Our findings suggest that common magnitude systems are more widespread among animals than previously believed and need not be cortically dependent in all species.
      Teaser Work with mammals has shown that the temporal, spatial, and numerical features of a stimulus often interact with one another. Current theories suggest that the parietal cortex mediates these effects. De Corte et al. challenge this notion with evidence that pigeons, which lack a laminar cortex, also show systematic space–time interactions,.

      PubDate: 2017-12-08T14:56:14Z
       
  • Reduced social-information provision by immigrants and use by residents
           following dispersal
    • Abstract: Publication date: 4 December 2017
      Source:Current Biology, Volume 27, Issue 23
      Author(s): Julie M. Kern, Andrew N. Radford
      Greater access to social information is a proposed benefit of group living [1]. However, individuals vary in the quantity and quality of information they provide [2], and prior knowledge about signaller reliability is likely important when receivers decide how to respond [3]. While dispersal causes regular changes in group membership [4], no experimental work has investigated social-information provision and use in this context. We studied sentinel behaviour following immigration in a habituated population of wild dwarf mongooses (Helogale parvula) [5]; sentinels (raised guards) use various vocalisations to provide social information [5,6]. Recent immigrants acted as sentinels rarely and significantly less often than residents, limiting their role as social-information providers. Even when recent immigrants acted as social-information providers, foragers responded to them less than they did to residents. Several months after arrival, immigrants had increased sentinel contributions, and foragers no longer responded differently to sentinel activity by former immigrants and residents. Our results raise questions about the assumed social-information benefits associated with increased group size.
      Teaser Greater access to social information is a proposed benefit of group living. However, Kern & Radford use long-term data and field experiments to show that social-information provision and use is lower than expected following dispersal events in dwarf mongooses. Group-living benefits should not be assumed, but may change with social circumstances.

      PubDate: 2017-12-08T14:56:14Z
       
  • Animal Communication: Origins of Sequential Structure in Birdsong
    • Abstract: Publication date: 4 December 2017
      Source:Current Biology, Volume 27, Issue 23
      Author(s): Ofer Tchernichovski, Dina Lipkind
      Culturally transmitted behaviors have an innate foundation, but the detailed sequential structure of such complex, acquired behaviors is often an outcome of historical accidents. New research has identified innate predispositions for structuring vocal sequences in culturally acquired birdsong.
      Teaser Culturally transmitted behaviors have an innate foundation, but the detailed sequential structure of such complex, acquired behaviors is often an outcome of historical accidents. New research has identified innate predispositions for structuring vocal sequences in culturally acquired birdsong.

      PubDate: 2017-12-08T14:56:14Z
       
  • Evolution: New Gene-Rich Mitochondria Found across the Eukaryotic Tree
    • Abstract: Publication date: 4 December 2017
      Source:Current Biology, Volume 27, Issue 23
      Author(s): Celine Petitjean, Tom A. Williams
      Mitochondria are the energy-generating organelles that power eukaryotic cells. Originally descended from endosymbiotic bacteria, their genomes have shrunk during evolution. New analyses suggest that large, gene-rich mitochondrial genomes are more common than previously thought, with interesting implications for eukaryotic genome evolution.
      Teaser Mitochondria are the energy-generating organelles that power eukaryotic cells. Originally descended from endosymbiotic bacteria, their genomes have shrunk during evolution. New analyses suggest that large, gene-rich mitochondrial genomes are more common than previously thought, with interesting implications for eukaryotic genome evolution.

      PubDate: 2017-12-08T14:56:14Z
       
  • Cortical Processing: How Mice Predict the Visual Effects of Locomotion
    • Abstract: Publication date: 4 December 2017
      Source:Current Biology, Volume 27, Issue 23
      Author(s): Marina Fridman, Leopoldo Petreanu
      New research identifies a frontal area in the mouse neocortex that sends predictions of locomotion-coupled visual flow to visual cortex. The findings support predictive coding theories of cortical processing.
      Teaser New research identifies a frontal area in the mouse neocortex that sends predictions of locomotion-coupled visual flow to visual cortex. The findings support predictive coding theories of cortical processing.

      PubDate: 2017-12-08T14:56:14Z
       
  • Actin Networks: Adapting to Load through Geometry
    • Abstract: Publication date: 4 December 2017
      Source:Current Biology, Volume 27, Issue 23
      Author(s): Klemens Rottner, Frieda Kage
      Cell migration frequently involves the protrusion of lamellipodial actin networks, the structure and regulation of which have been studied for decades. New work highlights how the geometry of these networks endows cells with the ability to adapt to environmental conditions and load.
      Teaser Cell migration frequently involves the protrusion of lamellipodial actin networks, the structure and regulation of which have been studied for decades. New work highlights how the geometry of these networks endows cells with the ability to adapt to environmental conditions and load.

      PubDate: 2017-12-08T14:56:14Z
       
  • Plant Development: Keeping on the Straight and Narrow and Flat
    • Abstract: Publication date: 4 December 2017
      Source:Current Biology, Volume 27, Issue 23
      Author(s): Michael Lenhard
      Plant leaves have functionally specialized upper and lower sides. Two recent studies show that these opposite identities are derived from a pre-pattern in the shoot meristem and the border between them is maintained by mobile small RNAs with morphogen-like properties.
      Teaser Plant leaves have functionally specialized upper and lower sides. Two recent studies show that these opposite identities are derived from a pre-pattern in the shoot meristem and the border between them is maintained by mobile small RNAs with morphogen-like properties.

      PubDate: 2017-12-08T14:56:14Z
       
  • Microbial Ecology: Community Coalescence Stirs Things Up
    • Abstract: Publication date: 4 December 2017
      Source:Current Biology, Volume 27, Issue 23
      Author(s): Matthias C. Rillig, India Mansour
      When methane-producing microbial communities are mixed experimentally, the resulting community is dominated by the community with the greatest resource-use efficiency. These results suggest a degree of community cohesion, or the maintenance of that initial community in the mix.
      Teaser When methane-producing microbial communities are mixed experimentally, the resulting community is dominated by the community with the greatest resource-use efficiency. These results suggest a degree of community cohesion, or the maintenance of that initial community in the mix.

      PubDate: 2017-12-08T14:56:14Z
       
  • Evolution: Weevils Get Tough on Symbiotic Tyrosine
    • Abstract: Publication date: 4 December 2017
      Source:Current Biology, Volume 27, Issue 23
      Author(s): Colin Dale
      Weevils, which represent one of the most diverse groups of terrestrial insects in nature, obtain a tough exoskeleton through the activity of an ancient bacterial symbiont with a tiny genome that serves as a factory for the production of tyrosine.
      Teaser Weevils, which represent one of the most diverse groups of terrestrial insects in nature, obtain a tough exoskeleton through the activity of an ancient bacterial symbiont with a tiny genome that serves as a factory for the production of tyrosine.

      PubDate: 2017-12-08T14:56:14Z
       
  • Protein Targeting: ER Leads the Way to the Inner Nuclear Envelope
    • Abstract: Publication date: 4 December 2017
      Source:Current Biology, Volume 27, Issue 23
      Author(s): Craig Blackstone
      Efficient targeting of newly synthesized membrane proteins from the endoplasmic reticulum to the inner nuclear membrane depends on nucleotide hydrolysis. A new study shows that this dependence reflects critical actions of the atlastin family of GTPases in maintaining the morphology of the endoplasmic reticulum network.
      Teaser Efficient targeting of newly synthesized membrane proteins from the endoplasmic reticulum to the inner nuclear membrane depends on nucleotide hydrolysis. A new study shows that this dependence reflects critical actions of the atlastin family of GTPases in maintaining the morphology of the endoplasmic reticulum network.

      PubDate: 2017-12-08T14:56:14Z
       
  • Causes and Consequences of Microtubule Acetylation
    • Abstract: Publication date: 4 December 2017
      Source:Current Biology, Volume 27, Issue 23
      Author(s): Carsten Janke, Guillaume Montagnac
      Among the different types of cytoskeletal components, microtubules arguably accumulate the greatest diversity of post-translational modifications (PTMs). Acetylation of lysine 40 (K40) of α-tubulin has received particular attention because it is the only tubulin PTM to be found in the lumen of microtubules: most other tubulin PTMs are found at the outer surface of the microtubule. As a consequence, the enzyme catalyzing K40 acetylation needs to penetrate the narrow microtubule lumen to find its substrate. Acetylated microtubules have been considered to be stable, long-lived microtubules; however, until recently, there was little information about whether the longevity of these microtubules is the cause or the consequence of acetylation. Current advances suggest that this PTM helps the microtubule lattice to cope with mechanical stress, thus facilitating microtubule self-repair. These observations now shed new light on the structural integrity of microtubules, as well as on the mechanisms and biological functions of tubulin acetylation. Here, we discuss recent insights into how acetylation is generated in the lumen of microtubules, and how this ‘hidden’ PTM can control the properties and functions of microtubules.
      Teaser In this Review, Janke and Montagnac discuss recent insights into the mechanisms responsible for acetylation in the lumen of microtubules and the effects of this luminal post-translational modification on the properties and functions of microtubules.

      PubDate: 2017-12-08T14:56:14Z
       
  • Local Signals in Mouse Horizontal Cell Dendrites
    • Abstract: Publication date: 4 December 2017
      Source:Current Biology, Volume 27, Issue 23
      Author(s): Camille A. Chapot, Christian Behrens, Luke E. Rogerson, Tom Baden, Sinziana Pop, Philipp Berens, Thomas Euler, Timm Schubert
      The mouse retina contains a single type of horizontal cell, a GABAergic interneuron that samples from all cone photoreceptors within reach and modulates their glutamatergic output via parallel feedback mechanisms. Because horizontal cells form an electrically coupled network, they have been implicated in global signal processing, such as large-scale contrast enhancement. Recently, it has been proposed that horizontal cells can also act locally at the level of individual cone photoreceptors. To test this possibility physiologically, we used two-photon microscopy to record light stimulus-evoked Ca2+ signals in cone axon terminals and horizontal cell dendrites as well as glutamate release in the outer plexiform layer. By selectively stimulating the two mouse cone opsins with green and UV light, we assessed whether signals from individual cones remain isolated within horizontal cell dendritic tips or whether they spread across the dendritic arbor. Consistent with the mouse’s opsin expression gradient, we found that the Ca2+ signals recorded from dendrites of dorsal horizontal cells were dominated by M-opsin and those of ventral horizontal cells by S-opsin activation. The signals measured in neighboring horizontal cell dendritic tips varied markedly in their chromatic preference, arguing against global processing. Rather, our experimental data and results from biophysically realistic modeling support the idea that horizontal cells can process cone input locally, extending the classical view of horizontal cell function. Pharmacologically removing horizontal cells from the circuitry reduced the sensitivity of the cone signal to low frequencies, suggesting that local horizontal cell feedback shapes the temporal properties of cone output.
      Teaser Chapot et al. show that local light responses in mouse horizontal cell dendrites inherit properties, including chromatic preference, from the presynaptic cone photoreceptor, suggesting that their dendrites can provide private feedback to cones, for instance, to shape the temporal filtering properties of the cone synapse.

      PubDate: 2017-12-08T14:56:14Z
       
  • Fbxl4 Serves as a Clock Output Molecule that Regulates Sleep through
           Promotion of Rhythmic Degradation of the GABAA Receptor
    • Abstract: Publication date: 4 December 2017
      Source:Current Biology, Volume 27, Issue 23
      Author(s): Qian Li, Yi Li, Xiao Wang, Junxia Qi, Xi Jin, Huawei Tong, Zikai Zhou, Zi Chao Zhang, Junhai Han
      The timing of sleep is tightly governed by the circadian clock, which contains a negative transcriptional feedback loop and synchronizes the physiology and behavior of most animals to daily environmental oscillations. However, how the circadian clock determines the timing of sleep is largely unclear. In vertebrates and invertebrates, the status of sleep and wakefulness is modulated by the electrical activity of pacemaker neurons that are circadian regulated and suppressed by inhibitory GABAergic inputs. Here, we showed that Drosophila GABAA receptors undergo rhythmic degradation in arousal-promoting large ventral lateral neurons (lLNvs) and their expression level in lLNvs displays a daily oscillation. We also demonstrated that the E3 ligase Fbxl4 promotes GABAA receptor ubiquitination and degradation and revealed that the transcription of fbxl4 in lLNvs is CLOCK dependent. Finally, we demonstrated that Fbxl4 regulates the timing of sleep through rhythmically reducing GABA sensitivity to modulate the excitability of lLNvs. Our study uncovered a critical molecular linkage between the circadian clock and the electrical activity of pacemaker neurons and demonstrated that CLOCK-dependent Fbxl4 expression rhythmically downregulates GABAA receptor level to increase the activity of pacemaker neurons and promote wakefulness.
      Teaser The circadian clock regulates the timing of sleep, but the underlying mechanisms are still not fully understood. Li et al. showed that CLOCK-dependent Fbxl4 expression rhythmically downregulated GABAA receptors to increase the activity of pacemaker neurons and promote wakefulness.

      PubDate: 2017-12-08T14:56:14Z
       
  • Stall in Canonical Autophagy-Lysosome Pathways Prompts Nucleophagy-Based
           Nuclear Breakdown in Neurodegeneration
    • Abstract: Publication date: 4 December 2017
      Source:Current Biology, Volume 27, Issue 23
      Author(s): Olga Baron, Adel Boudi, Catarina Dias, Michael Schilling, Anna Nölle, Gema Vizcay-Barrena, Ivan Rattray, Heinz Jungbluth, Wiep Scheper, Roland A. Fleck, Gillian P. Bates, Manolis Fanto
      The terminal stages of neuronal degeneration and death in neurodegenerative diseases remain elusive. Autophagy is an essential catabolic process frequently failing in neurodegeneration. Selective autophagy routes have recently emerged, including nucleophagy, defined as degradation of nuclear components by autophagy. Here, we show that, in a mouse model for the polyglutamine disease dentatorubral-pallidoluysian atrophy (DRPLA), progressive acquirement of an ataxic phenotype is linked to severe cerebellar cellular pathology, characterized by nuclear degeneration through nucleophagy-based LaminB1 degradation and excretion. We find that canonical autophagy is stalled in DRPLA mice and in human fibroblasts from patients of DRPLA. This is evidenced by accumulation of p62 and downregulation of LC3-I/II conversion as well as reduced Tfeb expression. Chronic autophagy blockage in several conditions, including DRPLA and Vici syndrome, an early-onset autolysosomal pathology, leads to the activation of alternative clearance pathways including Golgi membrane-associated and nucleophagy-based LaminB1 degradation and excretion. The combination of these alternative pathways and canonical autophagy blockade, results in dramatic nuclear pathology with disruption of the nuclear organization, bringing about terminal cell atrophy and degeneration. Thus, our findings identify a novel progressive mechanism for the terminal phases of neuronal cell degeneration and death in human neurodegenerative diseases and provide a link between autophagy block, activation of alternative pathways for degradation, and excretion of cellular components.
      Teaser Golgi-mediated degradation and excretion of LaminB1 promote cell atrophy and death. Baron et al. demonstrate that a block in canonical autophagy signaling leads to activation of alternative clearance routes. Golgi-mediated degradation and excretion of nuclear LaminB1 finally result in terminal nuclear breakdown, cell atrophy, and death.

      PubDate: 2017-12-08T14:56:14Z
       
  • Learning Biases Underlie “Universals” in Avian Vocal
           Sequencing
    • Abstract: Publication date: 4 December 2017
      Source:Current Biology, Volume 27, Issue 23
      Author(s): Logan S. James, Jon T. Sakata
      Biological predispositions in vocal learning have been proposed to underlie commonalities in vocal sequences, including for speech and birdsong, but cultural propagation could also account for such commonalities [1–4]. Songbirds such as the zebra finch learn the sequencing of their acoustic elements (“syllables”) during development [5–8]. Zebra finches are not constrained to learn a specific sequence of syllables, but significant consistencies in the positioning and sequencing of syllables have been observed between individuals within populations and between populations [8–10]. To reveal biological predispositions in vocal sequence learning, we individually tutored juvenile zebra finches with randomized and unbiased sequences of syllables and analyzed the extent to which birds produced common sequences. In support of biological predispositions, birds tutored with randomized sequences produced songs with striking similarities. Birds preferentially started and ended their song sequence with particular syllables, consistently positioned shorter and higher frequency syllables in the middle of their song, and sequenced their syllables such that pitch alternated across adjacent syllables. These patterns are reminiscent of those observed in normally tutored birds, suggesting that birds “creolize” aberrant sequence inputs to produce normal sequence outputs. Similar patterns were also observed for syllables that were not used for tutoring (i.e., unlearned syllables), suggesting that motor biases could contribute to sequence learning biases. Furthermore, zebra finches spontaneously produced acoustic patterns that are commonly observed in speech and music, suggesting that sensorimotor processes that are shared across a wide range of vertebrates could underlie these patterns in humans.
      Graphical abstract image Teaser James and Sakata reveal that naive zebra finches individually tutored with randomized acoustic sequences produce convergent acoustic patterns that are non-random and similar to those observed in wild finch song and in speech and music. Their data demonstrate that learning biases contribute to commonalities in acoustic patterning.

      PubDate: 2017-12-08T14:56:14Z
       
  • The Stone Age Plague and Its Persistence in Eurasia
    • Abstract: Publication date: 4 December 2017
      Source:Current Biology, Volume 27, Issue 23
      Author(s): Aida Andrades Valtueña, Alissa Mittnik, Felix M. Key, Wolfgang Haak, Raili Allmäe, Andrej Belinskij, Mantas Daubaras, Michal Feldman, Rimantas Jankauskas, Ivor Janković, Ken Massy, Mario Novak, Saskia Pfrengle, Sabine Reinhold, Mario Šlaus, Maria A. Spyrou, Anna Szécsényi-Nagy, Mari Tõrv, Svend Hansen, Kirsten I. Bos, Philipp W. Stockhammer, Alexander Herbig, Johannes Krause
      Yersinia pestis, the etiologic agent of plague, is a bacterium associated with wild rodents and their fleas. Historically it was responsible for three pandemics: the Plague of Justinian in the 6th century AD, which persisted until the 8th century [1]; the renowned Black Death of the 14th century [2, 3], with recurrent outbreaks until the 18th century [4]; and the most recent 19th century pandemic, in which Y. pestis spread worldwide [5] and became endemic in several regions [6]. The discovery of molecular signatures of Y. pestis in prehistoric Eurasian individuals and two genomes from Southern Siberia suggest that Y. pestis caused some form of disease in humans prior to the first historically documented pandemic [7]. Here, we present six new European Y. pestis genomes spanning the Late Neolithic to the Bronze Age (LNBA; 4,800 to 3,700 calibrated years before present). This time period is characterized by major transformative cultural and social changes that led to cross-European networks of contact and exchange [8, 9]. We show that all known LNBA strains form a single putatively extinct clade in the Y. pestis phylogeny. Interpreting our data within the context of recent ancient human genomic evidence that suggests an increase in human mobility during the LNBA, we propose a possible scenario for the early spread of Y. pestis: the pathogen may have entered Europe from Central Eurasia following an expansion of people from the steppe, persisted within Europe until the mid-Bronze Age, and moved back toward Central Eurasia in parallel with human populations.
      Teaser Andrades Valtueña et al. present the first six European Y. pestis genomes dating from the Late Neolithic and the Early Bronze Age. These data suggest that Y. pestis entered Europe during a human migration around 4800 BP, persisted in Europe, and traveled back to Central Eurasia.

      PubDate: 2017-12-08T14:56:14Z
       
  • Disruption of Perceptual Learning by a Brief Practice Break
    • Abstract: Publication date: 4 December 2017
      Source:Current Biology, Volume 27, Issue 23
      Author(s): David F. Little, Yu-Xuan Zhang, Beverly A. Wright
      Some forms of associative learning require only a single experience to create a lasting memory [1, 2]. In contrast, perceptual learning often requires extensive practice within a day for performance to improve across days [3, 4]. This suggests that the requisite practice for durable perceptual learning is integrated throughout each day. If the total amount of daily practice is the only important variable, then a practice break within a day should not disrupt across-day improvement. To test this idea, we trained human listeners on an auditory frequency-discrimination task over multiple days and compared the performance of those who engaged in a single continuous practice session each day [4] with those who were given a 30-min break halfway through each practice session. Continuous practice yielded significant perceptual learning [4]. In contrast, practice with a rest break led to no improvement, indicating that the integration process had decayed within 30 min. In a separate experiment, a 30-min practice break also disrupted durable learning on a non-native phonetic classification task. These results suggest that practice trials are integrated up to a learning threshold within a transient memory store before they are sent en masse into a memory that lasts across days. Thus, the oft cited benefits of distributed over massed training [5, 6] may arise from different mechanisms depending on whether the breaks occur before or after a learning threshold has been reached. Trial integration could serve as an early gatekeeper to plasticity, helping to ensure that longer-lasting changes are only made when deemed worthwhile.
      Teaser Little et al. find that a 30-min practice break during perceptual training prevents perceptual learning from lasting across days, suggesting that trials integrate up to a learning threshold within a transient memory store before they are sent en masse into a durable memory.

      PubDate: 2017-12-08T14:56:14Z
       
  • Homing Ants Get Confused When Nest Cues Are Also Route Cues
    • Abstract: Publication date: 4 December 2017
      Source:Current Biology, Volume 27, Issue 23
      Author(s): Roman Huber, Markus Knaden
      The desert ant Cataglyphis fortis inhabits the salt pans of Tunisia. Individual ants leave the nest for foraging trips that can cover distances of more than 1,500 m [1]. Homing ants use path integration [2, 3], but they also rely on visual [4] and olfactory [5] nest-defining cues to locate the nest entrance. However, nest cues can become ambiguous when they are ubiquitous in the environment. Here we show how ants behave during the nest search when the same cues occur at the nest and along the route. Homing ants focused their search narrowly around a visual or olfactory cue that in training they had experienced only at the nest. However, when ants were trained to the same cue not only at the nest but also repeatedly along the foraging route, they later exhibited a less focused search around the cue. This uncertainty was eliminated when ants had a composite cue at the nest that consisted of two components, one unique to the nest and another that also occurred along the route. Here, the ants focused their search on that part of the binary blend that was presented only at the nest and ignored the other, ubiquitous component. Ants thus not only seem to be able to pinpoint their nest by following learned visual and olfactory cues, but also take into account which cues uniquely specify the nest and which, due to their ubiquity, are less informative and so less reliable. Video
      Teaser Homing ants localize the nest by help of visual and olfactory cues. Huber and Knaden show that the ants focus their nest search on those cues that they experience at the nest only and ignore cues that are omnipresent in the environment. Ants even focus on the unambiguous parts of compound cues when parts of these cues are less informative.

      PubDate: 2017-12-08T14:56:14Z
       
  • A New Lineage of Eukaryotes Illuminates Early Mitochondrial Genome
           Reduction
    • Abstract: Publication date: 4 December 2017
      Source:Current Biology, Volume 27, Issue 23
      Author(s): Jan Janouškovec, Denis V. Tikhonenkov, Fabien Burki, Alexis T. Howe, Forest L. Rohwer, Alexander P. Mylnikov, Patrick J. Keeling
      The origin of eukaryotic cells represents a key transition in cellular evolution and is closely tied to outstanding questions about mitochondrial endosymbiosis [1, 2]. For example, gene-rich mitochondrial genomes are thought to be indicative of an ancient divergence, but this relies on unexamined assumptions about endosymbiont-to-host gene transfer [3–5]. Here, we characterize Ancoracysta twista, a new predatory flagellate that is not closely related to any known lineage in 201-protein phylogenomic trees and has a unique morphology, including a novel type of extrusome (ancoracyst). The Ancoracysta mitochondrion has a gene-rich genome with a coding capacity exceeding that of all other eukaryotes except the distantly related jakobids and Diphylleia, and it uniquely possesses heterologous, nucleus-, and mitochondrion-encoded cytochrome c maturase systems. To comprehensively examine mitochondrial genome reduction, we also assembled mitochondrial genomes from picozoans and colponemids and re-annotated existing mitochondrial genomes using hidden Markov model gene profiles. This revealed over a dozen previously overlooked mitochondrial genes at the level of eukaryotic supergroups. Analysis of trends over evolutionary time demonstrates that gene transfer to the nucleus was non-linear, that it occurred in waves of exponential decrease, and that much of it took place comparatively early, massively independently, and with lineage-specific rates. This process has led to differential gene retention, suggesting that gene-rich mitochondrial genomes are not a product of their early divergence. Parallel transfer of mitochondrial genes and their functional replacement by new nuclear factors are important in models for the origin of eukaryotes, especially as major gaps in our knowledge of eukaryotic diversity at the deepest level remain unfilled.
      Teaser Janouškovec et al. describe a new deep-branching eukaryote containing a gene-rich mitochondrial genome and heterologous systems for cytochrome c maturation. Comparative mitochondrial genomics provides insights into the position of the eukaryotic root and reveals parallel, lineage-specific, and exponentially decreasing gene transfer to the nucleus.

      PubDate: 2017-12-08T14:56:14Z
       
  • Trans-endocytosis of Planar Cell Polarity Complexes during Cell Division
    • Abstract: Publication date: 4 December 2017
      Source:Current Biology, Volume 27, Issue 23
      Author(s): Bryan W. Heck, Danelle Devenport
      To coordinate epithelial architecture with proliferation, cell polarity proteins undergo extensive remodeling during cell division [1–3]. A dramatic example of polarity remodeling occurs in proliferative basal cells of mammalian epidermis whereupon cell division, transmembrane planar cell polarity (PCP) proteins are removed from the cell surface via bulk endocytosis [4]. PCP proteins form intercellular complexes, linked by Celsr1-mediated homophilic adhesion, that coordinate polarity non-autonomously between cells [5, 6]. Thus, the mitotic reorganization of PCP proteins must alter not only proteins intrinsic to the dividing cell but also their interacting partners on neighboring cells. Here, we show that intercellular Celsr1 complexes that connect dividing cells with their neighbors remain intact during mitotic internalization, resulting in an uptake of Celsr1 protein from interphase neighbors. Trans-internalized Celsr1 carries with it additional core PCP proteins, including the posteriorly enriched Fz6 and anteriorly enriched Vangl2. Cadherin-mediated homophilic adhesion is necessary for trans-endocytosis, and adhesive junctional PCP complexes appear to be destined for degradation upon internalization. Surprisingly, whereas Fz6 and Vangl2 both internalize in trans, Vangl2 proteins intrinsic to the dividing cell remain associated with the plasma membrane. Persistent Vangl2 stabilizes Celsr1 and impedes its internalization, suggesting that dissociation of Vangl2 from Celsr1 is a prerequisite for Celsr1 endocytosis. These results demonstrate an unexpected transfer of PCP complexes between neighbors and suggest that the Vangl2 population that persists at the membrane during cell division could serve as an internal cue for establishing PCP in new daughter cells.
      Teaser During cell division, planar cell polarity (PCP) proteins are removed from the cell surface via bulk endocytosis. Heck and Devenport show that during this process, intercellular PCP complexes remain associated and are trans-endocytosed into dividing cells. Vangl2, however, is retained at the membrane, where it may act as a cue to restore polarity.

      PubDate: 2017-12-08T14:56:14Z
       
  • A Peptide Signaling System that Rapidly Enforces Paternity in the Aedes
           aegypti Mosquito
    • Abstract: Publication date: 4 December 2017
      Source:Current Biology, Volume 27, Issue 23
      Author(s): Laura B. Duvall, Nipun S. Basrur, Henrik Molina, Conor J. McMeniman, Leslie B. Vosshall
      Female Aedes aegypti mosquitoes typically mate only once with one male in their lifetime, a behavior known as “monandry” [1]. This single mating event provisions the female with sufficient sperm to fertilize the >500 eggs she will produce during her ∼4- to 6-week lifespan in the laboratory [2]. Successful mating induces lifetime refractoriness to subsequent insemination by other males, enforcing the paternity of the first male [3–5]. Ae. aegypti mate in flight near human hosts [6], and females become refractory to remating within seconds [1, 3, 4], suggesting the existence of a rapid mechanism to prevent female remating. In this study, we implicate HP-I, an Aedes- and male-specific peptide transferred to females [7], and its cognate receptor in the female, NPYLR1 [8], in rapid enforcement of paternity. HP-I mutant males were ineffective in enforcing paternity when a second male was given access to the female within 1 hr. NPYLR1 mutant females produced mixed paternity offspring at high frequency, indicating acceptance of multiple mates. Synthetic HP-I injected into wild-type, but not NPYLR1 mutant, virgins reduced successful matings. Asian tiger mosquito (Ae. albopictus) HP-I peptides potently activated Ae. aegypti NPYLR1. Invasive Ae. albopictus males are known to copulate with and effectively sterilize Ae. aegypti females by causing them to reject future mates [9]. Cross-species transfer of sperm and active seminal fluid proteins including HP-I may contribute to this phenomenon. This signaling system promotes rapid paternity enforcement within Ae. aegypti but may promote local extinction in areas where they compete with Ae. albopictus.
      Graphical abstract image Teaser Duvall et al. describe a rapidly acting peptide and cognate receptor system that acts to enforce paternity in the Aedes aegypti mosquito within 1 hr of copulation. HP-I peptide is transferred from males to females, where it acts on its receptor, NPYLR1. Understanding paternity enforcement is key for vector control and interspecies competition.

      PubDate: 2017-12-08T14:56:14Z
       
  • The Plastid Genome in Cladophorales Green Algae Is Encoded by Hairpin
           Chromosomes
    • Abstract: Publication date: Available online 30 November 2017
      Source:Current Biology
      Author(s): Andrea Del Cortona, Frederik Leliaert, Kenny A. Bogaert, Monique Turmel, Christian Boedeker, Jan Janouškovec, Juan M. Lopez-Bautista, Heroen Verbruggen, Klaas Vandepoele, Olivier De Clerck
      Virtually all plastid (chloroplast) genomes are circular double-stranded DNA molecules, typically between 100 and 200 kb in size and encoding circa 80–250 genes. Exceptions to this universal plastid genome architecture are very few and include the dinoflagellates, where genes are located on DNA minicircles. Here we report on the highly deviant chloroplast genome of Cladophorales green algae, which is entirely fragmented into hairpin chromosomes. Short- and long-read high-throughput sequencing of DNA and RNA demonstrated that the chloroplast genes of Boodlea composita are encoded on 1- to 7-kb DNA contigs with an exceptionally high GC content, each containing a long inverted repeat with one or two protein-coding genes and conserved non-coding regions putatively involved in replication and/or expression. We propose that these contigs correspond to linear single-stranded DNA molecules that fold onto themselves to form hairpin chromosomes. The Boodlea chloroplast genes are highly divergent from their corresponding orthologs, and display an alternative genetic code. The origin of this highly deviant chloroplast genome most likely occurred before the emergence of the Cladophorales, and coincided with an elevated transfer of chloroplast genes to the nucleus. A chloroplast genome that is composed only of linear DNA molecules is unprecedented among eukaryotes, and highlights unexpected variation in plastid genome architecture.
      Teaser Del Cortona et al. describe intriguing features of the plastid genome of Cladophorales, which is fragmented into linear ssDNA molecules that fold into hairpin configurations due to the presence of inverted repeats. This architecture is unprecedented among eukaryotes, and highlights unexpected variation in plastid genome structure.

      PubDate: 2017-12-08T14:56:14Z
       
  • Improved Modeling of Compositional Heterogeneity Supports Sponges as
           Sister to All Other Animals
    • Abstract: Publication date: Available online 30 November 2017
      Source:Current Biology
      Author(s): Roberto Feuda, Martin Dohrmann, Walker Pett, Hervé Philippe, Omar Rota-Stabelli, Nicolas Lartillot, Gert Wörheide, Davide Pisani
      The relationships at the root of the animal tree have proven difficult to resolve, with the current debate focusing on whether sponges (phylum Porifera) or comb jellies (phylum Ctenophora) are the sister group of all other animals [1–5]. The choice of evolutionary models seems to be at the core of the problem because Porifera tends to emerge as the sister group of all other animals (“Porifera-sister”) when site-specific amino acid differences are modeled (e.g., [6, 7]), whereas Ctenophora emerges as the sister group of all other animals (“Ctenophora-sister”) when they are ignored (e.g., [8–11]). We show that two key phylogenomic datasets that previously supported Ctenophora-sister [10, 12] display strong heterogeneity in amino acid composition across sites and taxa and that no routinely used evolutionary model can adequately describe both forms of heterogeneity. We show that data-recoding methods [13–15] reduce compositional heterogeneity in these datasets and that models accommodating site-specific amino acid preferences can better describe the recoded datasets. Increased model adequacy is associated with significant topological changes in support of Porifera-sister. Because adequate modeling of the evolutionary process that generated the data is fundamental to recovering an accurate phylogeny [16–20], our results strongly support sponges as the sister group of all other animals and provide further evidence that Ctenophora-sister represents a tree reconstruction artifact.
      Graphical abstract image Teaser The relationships at the root of the animal tree are debated. Feuda et al. show that comb jellies emerge as the sister of all the other animals when the model inadequately describes the data. As modeling improves, sponges emerge in this position instead, indicating that trees placing the comb jellies at the root of the animals are artifactual.

      PubDate: 2017-12-08T14:56:14Z
       
  • Nigrotectal Stimulation Stops Interval Timing in Mice
    • Abstract: Publication date: Available online 30 November 2017
      Source:Current Biology
      Author(s): Koji Toda, Nicholas A. Lusk, Glenn D.R. Watson, Namsoo Kim, Dongye Lu, Haofang E. Li, Warren H. Meck, Henry H. Yin
      Considerable evidence implicates the basal ganglia in interval timing, yet the underlying mechanisms remain poorly understood. Using a novel behavioral task, we demonstrate that head-fixed mice can be trained to show the key features of timing behavior within a few sessions. Single-trial analysis of licking behavior reveals stepping dynamics with variable onset times, which is responsible for the canonical Gaussian distribution of timing behavior. Moreover, the duration of licking bouts decreased as mice became sated, showing a strong motivational modulation of licking bout initiation and termination. Using optogenetics, we examined the role of the basal ganglia output in interval timing. We stimulated a pathway important for licking behavior, the GABAergic output projections from the substantia nigra pars reticulata to the deep layers of the superior colliculus. We found that stimulation of this pathway not only cancelled licking but also delayed the initiation of anticipatory licking for the next interval in a frequency-dependent manner. By combining quantitative behavioral analysis with optogenetics in the head-fixed setup, we established a new approach for studying the neural basis of interval timing.
      Teaser Toda et al. design a novel paradigm to study interval timing in mice. Using optogenetic manipulations, the authors show that activation of the nigrotectal pathway not only suppresses ongoing behavior but also delays timing of future behavior. These results suggest that disrupting basal ganglia output can stop central networks underlying timing.

      PubDate: 2017-12-08T14:56:14Z
       
  • Theta Oscillations in the Human Medial Temporal Lobe during Real-World
           Ambulatory Movement
    • Abstract: Publication date: Available online 30 November 2017
      Source:Current Biology
      Author(s): Zahra M. Aghajan, Peter Schuette, Tony A. Fields, Michelle E. Tran, Sameed M. Siddiqui, Nicholas R. Hasulak, Thomas K. Tcheng, Dawn Eliashiv, Emily A. Mankin, John Stern, Itzhak Fried, Nanthia Suthana
      The theta rhythm—a slow (6–12 Hz) oscillatory component of the local field potential—plays a critical role in spatial navigation and memory by coordinating the activity of neuronal ensembles within the medial temporal lobe (MTL). Although theta has been extensively studied in freely moving rodents, its presence in humans has been elusive and primarily investigated in stationary subjects. Here we used a unique clinical opportunity to examine theta within the human MTL during untethered, real-world ambulatory movement. We recorded intracranial electroencephalographic activity from participants chronically implanted with the wireless NeuroPace responsive neurostimulator (RNS) and tracked their motion with sub-millimeter precision. Our data revealed that movement-related theta oscillations indeed exist in humans, such that theta power is significantly higher during movement than immobility. Unlike in rodents, however, theta occurs in short bouts, with average durations of ∼400 ms, which are more prevalent during fast versus slow movements. In a rare opportunity to study a congenitally blind participant, we found that both the prevalence and duration of theta bouts were increased relative to the sighted participants. These results provide critical support for conserved neurobiological characteristics of theta oscillations during ambulatory spatial navigation, while highlighting some fundamental differences across species in these oscillations between humans and rodents.
      Teaser Aghajan et al. record deep brain activity, during untethered freely moving behavior, from participants chronically implanted with depth electrodes. They demonstrate that 8 Hz theta oscillations, the hallmark of spatial navigation in rodents, also occur in humans, albeit in shorter bouts that are more prevalent during fast versus slow movements.

      PubDate: 2017-12-08T14:56:14Z
       
  • Maternal Brain TNF-α Programs Innate Fear in the Offspring
    • Abstract: Publication date: Available online 30 November 2017
      Source:Current Biology
      Author(s): Bojana Zupan, Bingfang Liu, Faten Taki, Judit Gal Toth, Miklos Toth
      Tumor necrosis factor alpha (TNF-α) is a cytokine that not only coordinates local and systemic immune responses [1, 2] but also regulates neuronal functions. Most prominently, glia-derived TNF-α has been shown to regulate homeostatic synaptic scaling [3–6], but TNF-α-null mice exhibited no apparent cognitive or emotional abnormalities. Instead, we found a TNF-α-dependent intergenerational effect, as mothers with a deficit in TNF-α programmed their offspring to exhibit low innate fear. Cross-fostering and conditional knockout experiments indicated that a TNF-α deficit in the maternal brain, rather than in the hematopoietic system, and during gestation was responsible for the low-fear offspring phenotype. The level of innate fear governs the balance between exploration/foraging and avoidance of predators and is thus fundamentally important in adaptation, fitness, and survival [7]. Because maternal exercise and activity are known to reduce both brain TNF-α [8] and offspring innate fear [9], whereas maternal stress has been reported to increase brain TNF-α [10] and offspring fear and anxiety [11, 12], maternal brain TNF-α may report environmental conditions to promote offspring behavioral adaptation to their anticipated postnatal environment.
      Teaser TNF-α regulates synaptic scaling, but Zupan et al. show that TNF-α-null mice exhibit no behavioral anomalies. Instead, a brain TNF-α deficit in dams results in low fear in offspring. As maternal activity reduces brain TNF-α and downregulates offspring fear, brain TNF-α may report environmental conditions and help optimize offspring behavioral adaptation.

      PubDate: 2017-12-08T14:56:14Z
       
  • Evolution and Genetics of Precocious Burrowing Behavior in Peromyscus Mice
    • Abstract: Publication date: Available online 30 November 2017
      Source:Current Biology
      Author(s): Hillery C. Metz, Nicole L. Bedford, Yangshu Linda Pan, Hopi E. Hoekstra
      A central challenge in biology is to understand how innate behaviors evolve between closely related species. One way to elucidate how differences arise is to compare the development of behavior in species with distinct adult traits [1]. Here, we report that Peromyscus polionotus is strikingly precocious with regard to burrowing behavior, but not other behaviors, compared to its sister species P. maniculatus. In P. polionotus, burrows were excavated as early as 17 days of age, whereas P. maniculatus did not build burrows until 10 days later. Moreover, the well-known differences in burrow architecture between adults of these species—P. polionotus adults excavate long burrows with an escape tunnel, whereas P. maniculatus dig short, single-tunnel burrows [2–4]—were intact in juvenile burrowers. To test whether this juvenile behavior is influenced by early-life environment, we reciprocally cross-fostered pups of both species. Fostering did not alter the characteristic burrowing behavior of either species, suggesting that these differences are genetic. In backcross hybrids, we show that precocious burrowing and adult tunnel length are genetically correlated and that a P. polionotus allele linked to tunnel length variation in adults is also associated with precocious onset of burrowing in juveniles, suggesting that the same genetic region—either a single gene with pleiotropic effects or linked genes—influences distinct aspects of the same behavior at these two life stages. These results raise the possibility that genetic variants affect behavioral drive (i.e., motivation) to burrow and thereby affect both the developmental timing and adult expression of burrowing behavior.
      Graphical abstract image Teaser Metz et al. find that oldfield mice, a species that digs long, complex burrows, also digs burrows earlier than its sister species. In hybrids, an allele linked to adult tunnel length also affects the timing of first burrow construction, suggesting that this genetic region influences different aspects of the same behavior across life stages.

      PubDate: 2017-12-08T14:56:14Z
       
  • TDP-43 Promotes Neurodegeneration by Impairing Chromatin Remodeling
    • Abstract: Publication date: Available online 16 November 2017
      Source:Current Biology
      Author(s): Amit Berson, Ashley Sartoris, Raffaella Nativio, Vivianna Van Deerlin, Jon B. Toledo, Sílvia Porta, Shichong Liu, Chia-Yu Chung, Benjamin A. Garcia, Virginia M.-Y. Lee, John Q. Trojanowski, F. Brad Johnson, Shelley L. Berger, Nancy M. Bonini
      Regulation of chromatin structure is critical for brain development and function. However, the involvement of chromatin dynamics in neurodegeneration is less well understood. Here we find, launching from Drosophila models of amyotrophic lateral sclerosis and frontotemporal dementia, that TDP-43 impairs the induction of multiple key stress genes required to protect from disease by reducing the recruitment of the chromatin remodeler Chd1 to chromatin. Chd1 depletion robustly enhances TDP-43-mediated neurodegeneration and promotes the formation of stress granules. Conversely, upregulation of Chd1 restores nucleosomal dynamics, promotes normal induction of protective stress genes, and rescues stress sensitivity of TDP-43-expressing animals. TDP-43-mediated impairments are conserved in mammalian cells, and, importantly, the human ortholog CHD2 physically interacts with TDP-43 and is strikingly reduced in level in temporal cortex of human patient tissue. These findings indicate that TDP-43-mediated neurodegeneration causes impaired chromatin dynamics that prevents appropriate expression of protective genes through compromised function of the chromatin remodeler Chd1/CHD2. Enhancing chromatin dynamics may be a treatment approach to amyotrophic lateral scleorosis (ALS)/frontotemporal dementia (FTD).
      Graphical abstract image Teaser Berson et al. show that TDP-43, a protein associated with ALS and FTD, impairs the stress response by interfering with the chromatin remodeling protein Chd1 in flies and CHD2 in mammalian cells. In turn, animals expressing TDP-43 are hypersensitive to various types of stressors, indicating that this impairment may promote neurodegeneration.

      PubDate: 2017-11-16T17:55:30Z
       
  • Bats Use Path Integration Rather Than Acoustic Flow to Assess Flight
           Distance along Flyways
    • Abstract: Publication date: Available online 16 November 2017
      Source:Current Biology
      Author(s): Gal Aharon, Meshi Sadot, Yossi Yovel
      Navigation can be achieved using different strategies from simple beaconing to complex map-based movement [1–4]. Bats display remarkable navigation capabilities, ranging from nightly commutes of several kilometers and up to seasonal migrations over thousands of kilometers [5]. Many bats have been suggested to fly along fixed routes termed “flyways,” when flying from their roost to their foraging sites [6]. Flyways commonly stretch along linear landscape elements such as tree lines, hedges, or rivers [7]. When flying along a flyway, bats must estimate the distance they have traveled in order to determine when to turn. This can be especially challenging when moving along a repetitive landscape. Some bats, like Kuhl’s pipistrelles, which we studied here, have limited vision [8] and were suggested to rely on bio-sonar for navigation. These bats could therefore estimate distance using three main sensory-navigation strategies, all of which we have examined: acoustic flow, acoustic landmarks, or path integration. We trained bats to fly along a linear flyway and land on a platform. We then tested their behavior when the platform was removed under different manipulations, including changing the acoustic flow, moving the start point, and adding wind. We found that bats do not require acoustic flow, which was hypothesized to be important for their navigation [9–15], and that they can perform the task without landmarks. Our results suggest that Kuhl’s pipistrelles use internal self-motion cues—also known as path integration—rather than external information to estimate flight distance for at least dozens of meters when navigating along linear flyways.
      Teaser Many bats use bio-sonar to navigate. How they do so is unknown. The ability to estimate flight distance is a basic prerequisite for navigation. Aharon et al. show that bats use internal movement-based information to navigate without a need for external sensory input. Namely, bats do not need acoustic landmarks or flow to estimate how far they flew.

      PubDate: 2017-11-16T17:55:30Z
       
  • Altered Structural Connectivity of the Left Visual Thalamus in
           Developmental Dyslexia
    • Abstract: Publication date: Available online 16 November 2017
      Source:Current Biology
      Author(s): Christa Müller-Axt, Alfred Anwander, Katharina von Kriegstein
      Developmental dyslexia is a highly prevalent reading disorder affecting about 5%–10% of children [1]. It is characterized by slow and/or inaccurate word recognition skills as well as by poor spelling and decoding abilities [2]. Partly due to technical challenges with investigating subcortical sensory structures, current research on dyslexia in humans by and large focuses on the cerebral cortex [3–7]. These studies found that dyslexia is typically associated with functional and structural alterations of a distributed left-hemispheric cerebral cortex network (e.g., [8, 9]). However, findings from animal models and post mortem studies in humans suggest that dyslexia might also be associated with structural alterations in subcortical sensory pathways [10–14] (reviewed in [7]). Whether these alterations also exist in dyslexia in vivo and how they relate to dyslexia symptoms is currently unknown. Here, we used ultra-high-resolution structural magnetic resonance imaging (MRI), diffusion MRI, and probabilistic tractography to investigate the structural connections of the visual sensory pathway in dyslexia in vivo. We discovered that individuals with dyslexia have reduced structural connections in the direct pathway between the left visual thalamus (lateral geniculate nucleus [LGN]) and left middle temporal area V5/MT, but not between the left LGN and left primary visual cortex. In addition, left V5/MT-LGN connectivity strength correlated with rapid naming abilities—a key deficit in dyslexia [15]. These findings provide the first evidence of specific structural alterations in the connections between the sensory thalamus and cortex in developmental dyslexia. The results challenge current standard models and provide novel evidence for the importance of cortico-thalamic interactions in explaining dyslexia.
      Teaser Müller-Axt et al. show that dyslexics have reduced connections in the direct pathway between the left visual thalamus and cortical area V5/MT. The strength of this pathway predicted a key dyslexia symptom, thereby challenging current dyslexia models and stressing the importance of interactions between cortex and sensory thalamus for cognition.

      PubDate: 2017-11-16T17:55:30Z
       
  • The Paradox of Environmental Symbiont Acquisition in Obligate Mutualisms
    • Abstract: Publication date: Available online 16 November 2017
      Source:Current Biology
      Author(s): Aaron C. Hartmann, Andrew H. Baird, Nancy Knowlton, Danwei Huang
      Mutually beneficial interactions between species (mutualisms) shaped the evolution of eukaryotes and remain critical to the survival of species globally [1, 2]. Theory predicts that hosts should pass mutualist symbionts to their offspring (vertical transmission) [3–8]. However, offspring acquire symbionts from the environment in a surprising number of species (horizontal acquisition) [9–12]. A classic example of this paradox is the reef-building corals, in which 71% of species horizontally acquire algal endosymbionts [9]. An untested hypothesis explaining this paradox suggests that horizontal acquisition allows offspring to avoid symbiont-induced harm early in life. We reconstructed the evolution of symbiont transmission across 252 coral species and detected evolutionary transitions consistent with costs of vertical transmission among broadcast spawners, whose eggs tend to be positively buoyant and aggregate at the sea surface. Broadcasters with vertical transmission produce eggs with traits that favor reduced buoyancy (less wax ester lipid) and rapid development to the swimming stage (small egg size), both of which decrease the amount of time offspring spend at the sea surface. Wax ester provisioning decreased after vertically transmitting species evolved brooding from broadcasting, indicating that reduced buoyancy evolves only when offspring bear symbionts. We conclude that horizontal acquisition protects offspring from damage caused by high light and temperatures near the sea surface while providing benefits from enhanced fertilization and outcrossing. These findings help explain why modes of symbiont transmission and reproduction are strongly associated in corals and highlight benefits of delaying mutualist partnerships, offering an additional hypothesis for the pervasiveness of this theoretically paradoxical strategy.
      Teaser Hartmann et al. find evolutionary support for a hypothesis explaining why many coral species do not pass algal symbionts to their offspring, despite their necessity later in life. In addition to allowing offspring to acquire beneficial symbionts, lacking symbionts at birth may allow offspring to avoid harm while being fertilized at the sea surface.

      PubDate: 2017-11-16T17:55:30Z
       
  • Microtubule Tip Tracking by the Spindle and Kinetochore Protein Ska1
           Requires Diverse Tubulin-Interacting Surfaces
    • Abstract: Publication date: Available online 16 November 2017
      Source:Current Biology
      Author(s): Julie K. Monda, Ian P. Whitney, Ekaterina V. Tarasovetc, Elizabeth Wilson-Kubalek, Ronald A. Milligan, Ekaterina L. Grishchuk, Iain M. Cheeseman
      The macromolecular kinetochore functions to generate interactions between chromosomal DNA and spindle microtubules [1]. To facilitate chromosome movement and segregation, kinetochores must maintain associations with both growing and shrinking microtubule ends. It is critical to define the proteins and their properties that allow kinetochores to associate with dynamic microtubules. The kinetochore-localized human Ska1 complex binds to microtubules and tracks with depolymerizing microtubule ends [2]. We now demonstrate that the Ska1 complex also autonomously tracks with growing microtubule ends in vitro, a key property that would allow this complex to act at kinetochores to mediate persistent associations with dynamic microtubules. To define the basis for Ska1 complex interactions with dynamic microtubules, we investigated the tubulin-binding properties of the Ska1 microtubule binding domain. In addition to binding to the microtubule lattice and dolastatin-induced protofilament-like structures, we demonstrate that the Ska1 microtubule binding domain can associate with soluble tubulin heterodimers and promote assembly of oligomeric ring-like tubulin structures. We generated mutations on distinct surfaces of the Ska1 microtubule binding domain that disrupt binding to soluble tubulin but do not prevent microtubule binding. These mutants display compromised microtubule tracking activity in vitro and result in defective chromosome alignment and mitotic progression in cells using a CRISPR/Cas9-based replacement assay. Our work supports a model in which multiple surfaces of Ska1 interact with diverse tubulin substrates to associate with dynamic microtubule polymers and facilitate optimal chromosome segregation.
      Teaser Monda and Whitney et al. demonstrate that the kinetochore-localized Ska1 complex autonomously tracks with both growing and depolymerizing microtubule ends in vitro and that this activity requires multiple microtubule binding surfaces. Ska1 mutants that bind microtubules, but are unable to tip track, result in defective mitotic progression in cells.

      PubDate: 2017-11-16T17:55:30Z
       
  • Auditory Sensitivity and Decision Criteria Oscillate at Different
           Frequencies Separately for the Two Ears
    • Abstract: Publication date: Available online 16 November 2017
      Source:Current Biology
      Author(s): Hao Tam Ho, Johahn Leung, David C. Burr, David Alais, Maria Concetta Morrone
      Many behavioral measures of visual perception fluctuate continually in a rhythmic manner, reflecting the influence of endogenous brain oscillations, particularly theta (∼4–7 Hz) and alpha (∼8–12 Hz) rhythms [1–3]. However, it is unclear whether these oscillations are unique to vision or whether auditory performance also oscillates [4, 5]. Several studies report no oscillatory modulation in audition [6, 7], while those with positive findings suffer from confounds relating to neural entrainment [8–10]. Here, we used a bilateral pitch-identification task to investigate rhythmic fluctuations in auditory performance separately for the two ears and applied signal detection theory (SDT) to test for oscillations of both sensitivity and criterion (changes in decision boundary) [11, 12]. Using uncorrelated dichotic white noise to induce a phase reset of oscillations, we demonstrate that, as with vision, both auditory sensitivity and criterion showed strong oscillations over time, at different frequencies: ∼6 Hz (theta range) for sensitivity and ∼8 Hz (low alpha range) for criterion, implying distinct underlying sampling mechanisms [13]. The modulation in sensitivity in left and right ears was in antiphase, suggestive of attention-like mechanisms sampling alternatively from the two ears.
      Teaser Using signal detection theory, Ho et al. report that both perceptual sensitivity and decision criterion oscillate in audition (at 6 Hz and 8 Hz, respectively). The oscillations in sensitivity suggest alternate sampling of the two ears by attention-like mechanisms. Rhythmic oscillations seem to be a general phenomenon of many aspects of perception.

      PubDate: 2017-11-16T17:55:30Z
       
  • Consistency of Spatial Representations in Rat Entorhinal Cortex Predicts
           Performance in a Reorientation Task
    • Abstract: Publication date: Available online 16 November 2017
      Source:Current Biology
      Author(s): Shahaf Weiss, Ghadeer Talhami, Xenia Gofman-Regev, Sophia Rapoport, David Eilam, Dori Derdikman
      Goal-directed behavior can be affected by environmental geometry. A classic example is the rectangular arena reorientation task, where subjects commonly confuse opposite but geometrically identical corners [1]. Until recently, little was known about how environmental geometry shapes spatial representations in a neurobehavioral context [2] (although see [3]). In the present study, we asked: Under what circumstances does the internal cognitive map predict behavior' And when does it fail to do so' To this end, we developed a variant of the classical reorientation task that allows for investigation of temporal dynamics of reorientation. We recorded head-direction (HD) cells and grid cells in the medial entorhinal cortex (MEC) of rats before, during, and after performing the task. MEC cells showed a bimodal response of being either aligned or rotated, relative to the free-foraging open-field sessions. Alignment was remarkably stable between disorientations and indicative of corner choice as a function of current and past alignment of spatial representations. Accordingly, when the cells showed consistent and properly aligned readout across multiple trials, behavioral choices were better predicted by HD and grid cell readout, with a probability of more than 70%. This was not the case when the cells did not show a stable consistent readout. Our findings indicate that entorhinal spatial representations predict corner choice, contingent on the stability and reliability of their readout. This work sets the stage for further studies on the link between the reliability of the neuronal signal and behavior, with implications for many brain systems in many organisms.
      Teaser Using a variation of the reorientation task, Weiss et al. find a role for the stability of orientation signals in the entorhinal cortex of rats. Alignment and stability of past and present representations predict corner choice and highlight the connection between reliability of the neuronal signal and behavioral decisions.

      PubDate: 2017-11-16T17:55:30Z
       
  • Genetic and Epigenetic Strategies Potentiate Gal4 Activation to Enhance
           Fitness in Recently Diverged Yeast Species
    • Abstract: Publication date: Available online 16 November 2017
      Source:Current Biology
      Author(s): Varun Sood, Jason H. Brickner
      Certain genes show more rapid reactivation for several generations following repression, a conserved phenomenon called epigenetic transcriptional memory. Following previous growth in galactose, GAL gene transcriptional memory confers a strong fitness benefit in Saccharomyces cerevisiae adapting to growth in galactose for up to 8 generations. A genetic screen for mutants defective for GAL gene memory revealed new insights into the molecular mechanism, adaptive consequences, and evolutionary history of memory. A point mutation in the Gal1 co-activator that disrupts the interaction with the Gal80 inhibitor specifically and completely disrupted memory. This mutation confirms that cytoplasmically inherited Gal1 produced during previous growth in galactose directly interferes with Gal80 repression to promote faster induction of GAL genes. This mitotically heritable mode of regulation is recently evolved; in a diverged Saccharomyces species, GAL genes show constitutively faster activation due to genetically encoded basal expression of Gal1. Thus, recently diverged species utilize either epigenetic or genetic strategies to regulate the same molecular mechanism. The screen also revealed that the central domain of the Gal4 transcription factor both regulates the stochasticity of GAL gene expression and potentiates stronger GAL gene activation in the presence of Gal1. The central domain is critical for GAL gene transcriptional memory; Gal4 lacking the central domain fails to potentiate GAL gene expression and is unresponsive to previous Gal1 expression.
      Teaser Sood and Brickner find that faster GAL gene induction during transcriptional memory accelerates adaptation to galactose and requires both previously produced Gal1 to relieve Gal80 repression and the Gal4 central domain, which potentiates stronger activation. Related yeasts use either genetic or epigenetic means to alter GAL gene activation rates.

      PubDate: 2017-11-16T17:55:30Z
       
 
 
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