Monday, October 24, 2011

Hot off the presses! Oct 25 Curr Biol

The Oct 25 issue of the Curr Biol is now up on Pubget (About Curr Biol): if you're at a subscribing institution, just click the link in the latest link at the home page. (Note you'll only be able to get all the PDFs in the issue if your institution subscribes to Pubget.)

Latest Articles Include:

  • Shining new light on the brain
    - Curr Biol 21(20):R831-R833 (2011)
    Optogenetics — a new methodology that involves expression of light-responsive proteins in specific groups of neurons, which can then be activated with light — has only been around for six years, but some researchers are already using it to target big psychiatric questions. Michael Gross reports.
  • Darwin's little Prince
    - Curr Biol 21(20):R833-R834 (2011)
  • Sten Grillner
    - Curr Biol 21(20):R835-R836 (2011)
  • Genetic drift
    - Curr Biol 21(20):R837-R838 (2011)
  • Right temporal TMS impairs voice detection
    - Curr Biol 21(20):R838-R839 (2011)
    Functional magnetic resonance imaging (fMRI) research has revealed bilateral cortical regions along the upper banks of the superior temporal sulci (STS) which respond preferentially to voices compared to non-vocal, environmental sounds [1] and [2] . This sensitivity is particularly pronounced in the right hemisphere. Voice perception models imply that these regions, referred to as the temporal voice areas (TVAs), could correspond to a first stage of voice-specific processing in auditory cortex [3] and [4] , after which different types of vocal information are processed in interacting but partially independent functional pathways. However, clear causal evidence for this claim is missing. Here we provide the first direct link between TVA activity and voice detection ability using repetitive transcranial magnetic stimulation (rTMS). Voice/non-voice discrimination ability was impaired when rTMS was targeted at the right TVA compared with a control site. In contrast, ! a lower-level loudness judgement task was not differentially affected by site of stimulation. Results imply that neuronal computations in the right TVA are necessary for the distinction between human voices and other, non-vocal sounds.
  • Morphogenesis: Forcing the Tissue
    - Curr Biol 21(20):R840-R841 (2011)
    How are the transcriptional events that control form actually transduced into the shape of an organism? Analysis of plant tissue mechanical properties shows that control of the extracellular matrix is key.
  • Vesicle Trafficking: A Rab Family Profile
    - Curr Biol 21(20):R841-R843 (2011)
    A new tool-kit has been developed for profiling expression and function of Rab GTPases on a genome-wide scale. Use of this tool-kit has revealed unexpectedly that at least half of Drosophila Rabs have neuronal-specific expression patterns and localize to synapses.
  • Animal Navigation: Following Signposts in the Sea
    - Curr Biol 21(20):R843-R846 (2011)
    The directional responses of turtles to simulated magnetic coordinates of positions in the sea have given insight into the turtles' route-like and map-like behaviour.
  • Mimicry: The Hunting of the Supergene
    - Curr Biol 21(20):R846-R848 (2011)
    Mimicry is an example of an adaptation that requires the integration of several components. Genetic characterisation of a mimicry polymorphism in a butterfly reveals the expected suppression of recombination among its components, preventing the production of unfit character combinations.
  • Cytokinesis: Cells Go Back and Forth about Division
    - Curr Biol 21(20):R848-R850 (2011)
    An elegant quantitative model to explain cellular oscillations during cytokinesis reveals a novel function for polar blebbing and raises the question as to why cells live right on the edge.
  • Embryonic Stem Cells: Testing the Germ-Cell Theory
    - Curr Biol 21(20):R850-R852 (2011)
    The exact cellular origin of embryonic stem cells remains elusive. Now a new study provides compelling evidence that embryonic stem cells, established under conventional culture conditions, originate from a transient germ-cell state.
  • Phagocytosis: Coupling of Mitochondrial Uncoupling and Engulfment
    - Curr Biol 21(20):R852-R854 (2011)
    Clearance of apoptotic cells by phagocytes avoids triggering an inflammatory response. A new study reveals that phagocytes dissipate their mitochondrial proton electrochemical gradient to allow for the ingestion of more apoptotic corpses. Mitochondria are therefore involved in all aspects of apoptosis, from its activation through to the phagocytosis of dead cells.
  • Developmental Biology: Physics Adds a Twist to Gut Looping
    - Curr Biol 21(20):R854-R857 (2011)
    Much of the effort in understanding the dynamic process of development has focused on dissecting biochemical pathways. Recent studies illustrate that simple physical forces are also important in patterning organs.
  • Mitotic Exit Control: A Space and Time Odyssey
    - Curr Biol 21(20):R857-R859 (2011)
    The mitotic exit network (MEN), a protein kinase cascade under the switch-like control of the small GTPase Tem1, triggers exit from mitosis in budding yeast. Now it emerges that signals from both Tem1 and the yeast Polo kinase Cdc5 converge onto the MEN kinase Cdc15 to accurately restrict MEN activation to late mitosis.
  • Transcriptional Repressors: Shutting Off Gene Expression at the Source Affects Developmental Dynamics
    - Curr Biol 21(20):R859-R860 (2011)
    Developmental networks feature genes interlinked by transcriptional activation and repression. A new study indicates that repressors can 'shut the door' to newly initiating polymerases, allowing longer target genes to produce latent transcripts after shorter genes have been effectively silenced.
  • Animal Orientation Strategies for Movement in Flows
    - Curr Biol 21(20):R861-R870 (2011)
    For organisms that fly or swim, movement results from the combined effects of the moving medium — air or water — and the organism's own locomotion. For larger organisms, propulsion contributes significantly to progress but the flow usually still provides significant opposition or assistance, or produces lateral displacement ('drift'). Animals show a range of responses to flows, depending on the direction of the flow relative to their preferred direction, the speed of the flow relative to their own self-propelled speed, the incidence of flows in different directions and the proportion of the journey remaining. We here present a classification of responses based on the direction of the resulting movement relative to flow and preferred direction, which is applicable to a range of taxa and environments. The responses adopted in particular circumstances are related to the organisms' locomotory and sensory capacities and the environmental cues available. Advances in ! biologging technologies and particle tracking models are now providing a wealth of data, which often demonstrate a striking level of convergence in the strategies that very different animals living in very different environments employ when moving in a flow.
  • The Tubulin Deglutamylase CCPP-1 Regulates the Function and Stability of Sensory Cilia in C. elegans
    - Curr Biol 21(20):1685-1694 (2011)
    Background Posttranslational modifications (PTMs) such as acetylation, detyrosination, and polyglutamylation have long been considered markers of stable microtubules and have recently been proposed to guide molecular motors to specific subcellular destinations. Microtubules can be deglutamylated by the cytosolic carboxypeptidase CCP1. Loss of CCP1 in mice causes cerebellar Purkinje cell degeneration. Cilia, which are conserved organelles that play important diverse roles in animal development and sensation, contain axonemes comprising microtubules that are especially prone to PTMs. Results Here, we report that a CCP1 homolog, CCPP-1, regulates the ciliary localization of the kinesin-3 KLP-6 and the polycystin PKD-2 in male-specific sensory neurons in C. elegans. In male-specific CEM (cephalic sensilla, male) cilia, ccpp-1 also controls the velocity of the kinesin-2 OSM-3/KIF17 without affecting the transport of kinesin-II cargo. In the core ciliated nervous system of both males and hermaphrodites, loss of ccpp-1 causes progressive defects in amphid and phasmid sensory cilia, suggesting that CCPP-1 activity is required for ciliary maintenance but not ciliogenesis. Affected cilia exhibit defective B-tubules. Loss of TTLL-4, a polyglutamylating enzyme of the tubulin tyrosine ligase-like family, suppresses progressive ciliary defects in ccpp-1 mutants. Conclusions Our studies suggest that CCPP-1 acts as a tubulin deglutamylase that regulates the localization and velocity of kinesin motors and the structural integrity of microtubules in sensory cilia of a multicellular, living animal. We propose that the neuronal degeneration caused by loss of CCP1 in mammals may represent a novel ciliopathy in which cilia are formed but not maintained, depriving the cell of cilia-based signal transduction.
  • Endogenous Transcription at the Centromere Facilitates Centromere Activity in Budding Yeast
    - Curr Biol 21(20):1695-1703 (2011)
    Background The centromere (CEN) DNA-kinetochore complex is the specialized chromatin structure that mediates chromosome attachment to the spindle and is required for high-fidelity chromosome segregation. Although kinetochore function is conserved from budding yeast to humans, it was thought that transcription had no role in centromere function in budding yeast, in contrast to other eukaryotes including fission yeast. Results We report here that transcription at the centromere facilitates centromere activity in the budding yeast Saccharomyces cerevisiae. We identified transcripts at CEN DNA and found that Cbf1, which is a transcription factor that binds to CEN DNA, is required for transcription at CEN DNA. Chromosome instability of cbf1Δ cells is suppressed by transcription driven from an artificial promoter. Furthermore, we have identified Ste12, which is a transcription factor, and Dig1, a Ste12 inhibitor, as a novel CEN-associated protein complex by an in vitro kinetochore assembly system. Dig1 represses Ste12-dependent transcription at the centromere. Conclusions Our studies reveal that transcription at the centromere plays an important role in centromere function in budding yeast.
  • Systematic Discovery of Rab GTPases with Synaptic Functions in Drosophila
    - Curr Biol 21(20):1704-1715 (2011)
    Background Neurons require highly specialized intracellular membrane trafficking, especially at synapses. Rab GTPases are considered master regulators of membrane trafficking in all cells, and only very few Rabs have known neuron-specific functions. Here, we present the first systematic characterization of neuronal expression, subcellular localization, and function of Rab GTPases in an organism with a brain. Results We report the surprising discovery that half of all Drosophila Rabs function specifically or predominantly in distinct subsets of neurons in the brain. Furthermore, functional profiling of the GTP/GDP-bound states reveals that these neuronal Rabs are almost exclusively active at synapses and the majority of these synaptic Rabs specifically mark synaptic recycling endosomal compartments. Our profiling strategy is based on Gal4 knockins in large genomic fragments that are additionally designed to generate mutants by ends-out homologous recombination. We generated 36 large genomic targeting vectors and transgenic rab-Gal4 fly strains for 25 rab genes. Proof-of-principle knockout of the synaptic rab27 reveals a sleep phenotype that matches its cell-specific expression. Conclusions Our findings suggest that up to half of all Drosophila Rabs exert specialized synaptic functions. The tools presented here allow systematic functional studies of these Rabs and provide a method that is applicable to any large gene family in Drosophila.
  • Guarding Males Protect Females from Predation in a Wild Insect
    - Curr Biol 21(20):1716-1719 (2011)
    Males frequently remain in close proximity to their mate immediately postcopulation. This behavior has generally been interpreted as a guarding tactic designed to reduce the likelihood that a rival male can rapidly displace the ejaculate of the guarding male [ [1] and [2] ]. Such attempts by males to control their mates represent a potential source of conflict [ [3] , [4] and [5] ], but guarding behaviors in species where it is difficult for males to control their mates suggest that conflict is not inevitable [ [6] and [7] ]. We employed a network of infrared video cameras to study a wild population of individually marked and genotyped field crickets (Gryllus campestris). Lone females or males suffer similar rates of predation, but when a pair is attacked, the male allows the female priority access to their burrow, and in doing so dramatically increases his probability of being killed. In compensation for this increased predation risk, paired males mate more fre! quently and father more of the female's offspring. By staying with a male, females increase the sperm contribution of preferred males as well as reducing their predation risk. In contrast to conclusions based on previous lab studies, our field study suggests that mate guarding can evolve in a context of cooperation rather than conflict between the sexes. Video Abstract View Within Article
  • Pectin-Induced Changes in Cell Wall Mechanics Underlie Organ Initiation in Arabidopsis
    - Curr Biol 21(20):1720-1726 (2011)
    Tissue mechanics have been shown to play a key role in the regulation of morphogenesis in animals [ [1] , [2] , [3] and [4] ] and may have an equally important role in plants [ [5] , [6] , [7] , [8] and [9] ]. The aerial organs of plants are formed at the shoot apical meristem following a specific phyllotactic pattern [10]. The initiation of an organ from the meristem requires a highly localized irreversible surface deformation, which depends on the demethylesterification of cell wall pectins [11]. Here, we used atomic force microscopy (AFM) to investigate whether these chemical changes lead to changes in tissue mechanics. By mapping the viscoelasticity and elasticity in living meristems, we observed increases in tissue elasticity, correlated with pectin demethylesterification, in primordia and at the site of incipient organs. Measurements of tissue elasticity at various depths showed that, at the site of incipient primordia, the first increases occurred in su! bepidermal tissues. The results support the following causal sequence of events: (1) demethylesterification of pectin is triggered in subepidermal tissue layers, (2) this contributes to an increase in elasticity of these layers—the first observable mechanical event in organ initiation, and (3) the process propagates to the epidermis during the outgrowth of the organ.
  • Reconstitution of Amoeboid Motility In Vitro Identifies a Motor-Independent Mechanism for Cell Body Retraction
    - Curr Biol 21(20):1727-1731 (2011)
    Crawling movement in eukaryotic cells requires coordination of leading-edge protrusion with cell body retraction [ [1] , [2] and [3] ]. Protrusion is driven by actin polymerization along the leading edge [4]. The mechanism of retraction is less clear; myosin contractility may be involved in some cells [5] but is not essential in others [ [6] , [7] , [8] and [9] ]. In Ascaris sperm, protrusion and retraction are powered by the major sperm protein (MSP) motility system instead of the conventional actin apparatus [ [10] and [11] ]. These cells lack motor proteins [12] and so are well suited to explore motor-independent mechanisms of retraction. We reconstituted protrusion and retraction simultaneously in MSP filament meshworks, called fibers, that assemble behind plasma membrane-derived vesicles. Retraction is triggered by depolymerization of complete filaments in the rear of the fiber [13]. The surviving filaments reorganize to maintain their packing density. By! packing fewer filaments into a smaller volume, the depolymerizing network shrinks and thereby generates sufficient force to move an attached load. Our work provides direct evidence for motor-independent retraction in the reconstituted MSP motility system of nematode sperm. This mechanism could also apply to actin-based cells and may explain reports of cells that crawl even when their myosin activity is compromised.
  • Nonretinotopic Exogenous Attention
    - Curr Biol 21(20):1732-1737 (2011)
    Attention is crucial for visual perception because it allows the visual system to effectively use its limited resources by selecting behaviorally and cognitively relevant stimuli from the large amount of information impinging on the eyes. Reflexive, stimulus-driven attention is essential for successful interactions with the environment because it can, for example, speed up responses to life-threatening events. It is commonly believed that exogenous attention operates in the retinotopic coordinates of the early visual system. Here, using a novel experimental paradigm [1], we show that a nonretinotopic cue improves both accuracy and reaction times in a visual search task. Furthermore, the influence of the cue is limited both in space and time, a characteristic typical of exogenous cueing. These and other recent findings show that many more aspects of vision are processed nonretinotopically than previously thought.
  • Mitochondrial Preprotein Translocase of Trypanosomatids Has a Bacterial Origin
    - Curr Biol 21(20):1738-1743 (2011)
    Mitochondria are found in all eukaryotic cells and derive from a bacterial endosymbiont [ [1] and [2] ]. The evolution of a protein import system was a prerequisite for the conversion of the endosymbiont into a true organelle. Tom40, the essential component of the protein translocase of the outer membrane, is conserved in mitochondria of almost all eukaryotes but lacks bacterial orthologs [ [3] , [4] , [5] and [6] ]. It serves as the gateway through which all mitochondrial proteins are imported. The parasitic protozoa Trypanosoma brucei and its relatives do not have a Tom40-like protein, which raises the question of how proteins are imported by their mitochondria [ [7] and [8] ]. Using a combination of bioinformatics and in vivo and in vitro studies, we have discovered that T. brucei likely employs a different import channel, termed ATOM (archaic translocase of the outer mitochondrial membrane). ATOM mediates the import of nuclear-encoded proteins into mitochon! dria and is essential for viability of trypanosomes. It is not related to Tom40 but is instead an ortholog of a subgroup of the Omp85 protein superfamily that is involved in membrane translocation and insertion of bacterial outer membrane proteins [9]. This suggests that the protein import channel in trypanosomes is a relic of an archaic protein transport system that was operational in the ancestor of all eukaryotes.
  • Adaptive Secondary Sex Ratio Adjustments via Sex-Specific Infanticide in a Bird
    - Curr Biol 21(20):1744-1747 (2011)
    Infanticide is easiest to understand when it involves killing the offspring of others [1], but a parent may also kill its own offspring if the sacrifice of currently dependent young leads to higher survival of brood mates [2] or an improvement in the parent's likely future reproduction [3]. However, sex-specific infanticide by parents of their own offspring, although occurring in some human societies [4], is rare across species. Its rarity may be because killing one sex combines wasted parental effort with consequent biases in population sex ratios that are detrimental for the fitness of the overproduced sex [ [5] , [6] and [7] ]. We show that killing male offspring can be advantageous to Eclectus parrot (Eclectus roratus) mothers even though frequency-dependent selection then elevates the reproductive value of sons above that of daughters. In poorer-quality nest hollows, broods with a single female nestling had higher reproductive value than broods in which the fem! ale had a younger brother. Our data demonstrate frequent targeted removal of male nestlings within 3 days of hatching in these specific brood types and nesting conditions. The ability of Eclectus parrots to perceive the sex of their offspring relatively early may favor decisions to kill one sex before further investment in parental care.
  • Emergent Growth Cone Responses to Combinations of Slit1 and Netrin 1 in Thalamocortical Axon Topography
    - Curr Biol 21(20):1748-1755 (2011)
    How guidance cues are integrated during the formation of complex axonal tracts remains largely unknown. Thalamocortical axons (TCAs), which convey sensory and motor information to the neocortex, have a rostrocaudal topographic organization initially established within the ventral telencephalon [ [1] , [2] and [3] ]. Here, we show that this topography is set in a small hub, the corridor, which contains matching rostrocaudal gradients of Slit1 and Netrin 1. Using in vitro and in vivo experiments, we show that Slit1 is a rostral repellent that positions intermediate axons. For rostral axons, although Slit1 is also repulsive and Netrin 1 has no chemotactic activity, the two factors combined generate attraction. These results show that Slit1 has a dual context-dependent role in TCA pathfinding and furthermore reveal that a combination of cues produces an emergent activity that neither of them has alone. Our study thus provides a novel framework to explain how a limited s! et of guidance cues can generate a vast diversity of axonal responses necessary for proper wiring of the nervous system.
  • Children, but Not Chimpanzees, Prefer to Collaborate
    - Curr Biol 21(20):1756-1758 (2011)
    Human societies are built on collaborative activities. Already from early childhood, human children are skillful and proficient collaborators. They recognize when they need help in solving a problem and actively recruit collaborators [ [1] and [2] ]. The societies of other primates are also to some degree cooperative. Chimpanzees, for example, engage in a variety of cooperative activities such as border patrols, group hunting, and intra- and intergroup coalitionary behavior [ [3] , [4] and [5] ]. Recent studies have shown that chimpanzees possess many of the cognitive prerequisites necessary for human-like collaboration. Chimpanzees have been shown to recognize when they need help in solving a problem and to actively recruit good over bad collaborators [ [6] and [7] ]. However, cognitive abilities might not be all that differs between chimpanzees and humans when it comes to cooperation. Another factor might be the motivation to engage in a cooperative activity. ! Here, we hypothesized that a key difference between human and chimpanzee collaboration—and so potentially a key mechanism in the evolution of human cooperation—is a simple preference for collaborating (versus acting alone) to obtain food. Our results supported this hypothesis, finding that whereas children strongly prefer to work together with another to obtain food, chimpanzees show no such preference.
  • Blimp1 Expression Predicts Embryonic Stem Cell Development In Vitro
    - Curr Biol 21(20):1759-1765 (2011)
    Despite recent critical insights into the pluripotent state of embryonic stem cells (ESCs), there is little agreement over the inaugural and subsequent steps leading to its generation [ [1] , [2] , [3] and [4] ]. Here we show that inner cell mass (ICM)-generated cells expressing Blimp1, a key transcriptional repressor of the somatic program during germ cell specification [ [5] and [6] ], emerge on day 2 of blastocyst culture. Single-cell gene expression profiling indicated that many of these Blimp1-positive cells coexpress other genes typically associated with early germ cell specification. When genetically traced in vitro, these cells acquired properties normally associated with primordial germ cells. Importantly, fate-mapping experiments revealed that ESCs commonly arise from Blimp1-positive precursors; indeed, prospective sorting of such cells from ICM outgrowths increased the rate of ESC derivation more than 9-fold. Finally, using genetic ablation or distinct! small molecules [ [7] and [8] ], we show that epiblast cells can become ESCs without first acquiring Blimp1 positivity. Our findings suggest that the germ cell-like state is facultative for the stabilization of pluripotency in vitro. Thus, the association of Blimp1 expression with ESC development furthers understanding of how the pluripotent state of these cells is established in vitro and suggests a means to enhance the generation of new stem cell lines from blastocysts.
  • Anterior Prefrontal Cortex Inhibition Impairs Control over Social Emotional Actions
    - Curr Biol 21(20):1766-1770 (2011)
    When dealing with emotional situations, we often need to rapidly override automatic stimulus-response mappings and select an alternative course of action [1], for instance, when trying to manage, rather than avoid, another's aggressive behavior. The anterior prefrontal cortex (aPFC) has been linked to the control of these social emotional behaviors [ [2] and [3] ]. We studied how this control is implemented by inhibiting the left aPFC with continuous theta burst stimulation (cTBS; [4]). The behavioral and cerebral consequences of this intervention were assessed with a task quantifying the control of social emotional actions and with concurrent measurements of brain perfusion. Inhibition of the aPFC led participants to commit more errors when they needed to select rule-driven responses overriding automatic action tendencies evoked by emotional faces. Concurrently, task-related perfusion decreased in bilateral aPFC and posterior parietal cortex and increased in amygdal! a and left fusiform face area. We infer that the aPFC controls social emotional behavior by upregulating regions involved in rule selection [5] and downregulating regions supporting the automatic evaluation of emotions [6]. These findings illustrate how exerting emotional control during social interactions requires the aPFC to coordinate rapid action selection processes, the detection of emotional conflicts, and the inhibition of emotionally-driven responses.
  • Ecological and Evolutionary Consequences of Linked Life-History Stages in the Sea
    - Curr Biol 21(20):1771 (2011)

No comments: