Monday, February 7, 2011

Hot off the presses! Feb 08 curr biol

The Feb 08 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:

  • Deep drilling moves ahead
    - curr biol 21(3):R93-R94 (2011)
    The Deepwater Horizon disaster has led to little delay in fresh oil drilling. Nigel Williams reports.
  • Seabed search boost
    - curr biol 21(3):R94-R95 (2011)
    Oceanography's newest deep-sea research submersible is also its oldest. Michael Gross reports.
  • New plans for wild areas
    - curr biol 21(3):R96-R97 (2011)
    Plans to extend protected lands in the US are causing controversy. Nigel Williams reports.
  • Profit of gloom
    - curr biol 21(3):R97-R98 (2011)
    The record price of 20.2 million yen ($350,000) for a single bluefin tuna at a high-profile New Year Tokyo fish market sale adds to the problems of conservationists seeking to substantially increase protection for the species. The 342 kg fish was bought at auction by the owners of Kyubey, a Tokyo sushi restaurant, and Itamae Sushi, a Hong Kong based restaurant chain.
  • Manfred Kayser
    - curr biol 21(3):R98-R99 (2011)
  • Kindlins
    - curr biol 21(3):R99-R101 (2011)
  • Polarisation vision
    - curr biol 21(3):R101-R105 (2011)
    Putting on a pair of polarised sunglasses is as close as most of us get to seeing polarised light. Photographers also use polarising filters and, in both cases, the reason for placing such filters in front of eye or camera is to reduce glare and increase contrast within the image or scene viewed. Animal visual systems also utilise polarised light for these purposes, along with navigation, sexual signalling and detecting water. They rarely, if ever, use optical filters to achieve polarisation sensitivity; instead it is an intrinsic property of their photoreceptors. Linear polarising sensitivity is common in the animal kingdom, particularly in invertebrates such as arthropods (insects, crustaceans and spiders) and cephalopods. Linear polarising sensitivity is also known in vertebrates, including fish, birds and a few amphibians and reptiles. In truth, this ability is probably more widespread than we think, and in the cephalopods and many crustaceans it may replace colour! vision. While circular polarising photography — used for cancer detection in medical imaging and for (explosive) mine detection underwater — might be considered an obscure man-made optical trick, some animals also have circular polarising sensitivity. Before going on to describe how and why animals utilise polarised light, we briefly examine what polarised light is, why it is called linear or circular, where it comes from and where it is frequently found in natural environments (Figure 1).
  • Structural and functional fractionation of right superior parietal cortex in bistable perception
    - curr biol 21(3):R106-R107 (2011)
    When faced with ambiguous sensory input, conscious awareness may alternate between the different percepts that are consistent with the input. Visual phenomena leading to such multistable perception, where constant sensory input evokes different conscious percepts, are particularly useful for investigating the processes underlying perceptual awareness [1]. Understanding the role that high-level brain regions outside early visual cortex play in perceptual alternations could elucidate how top-down processes modulate conscious perception [2]. In two studies [3] and [4] published recently in Current Biology, different combinations of the present authors used repetitive transcranial magnetic stimulation (rTMS) to disrupt activity in human superior parietal cortex, and reported seemingly contradictory results [5] concerning the effect of disrupting the normal function of this area on bistable perception. Here we join forces to resolve this discrepancy.
  • Repeated colonization and hybridization in Lake Malawi cichlids
    - curr biol 21(3):R108-R109 (2011)
    Through adaptive radiation, ancestral species rapidly diversify into multiple species with different ecological adaptations. The haplochromine cichlid fishes of the East African Great Lakes are considered classic examples of adaptive radiation, but our understanding of the evolutionary origins of these radiations has been limited by inadequate taxonomic and genomic sampling [1] and [2]. Perhaps the largest of these radiations is from Lake Malawi, estimated to contain between 500 and 800 endemic species. Surprisingly, its monophyly — the origin from a single ancestral species — has never been critically tested. This is because river populations which could have seeded the radiation, with one very limited exception [3], have never been included in phylogenetic reconstructions. Moreover, phylogenies have relied heavily on mitochondrial DNA (mtDNA), which can be a misleading phylogenetic marker for species capable of hybridization [4] and [5] because its non-recombinin! g nature means that transfer to other species can occur via asymmetric introgression and 'allele surfing' [6]. Here, we used broad taxonomic sampling and nuclear DNA markers with wide genomic coverage and find that the Lake Malawi radiation is not monophyletic, but instead contains genetic material from divergent riverine ancestors indicating multiple invasions and hybridization.
  • Chromosome Segregation: Keeping Kinetochores in the Loop
    - curr biol 21(3):R110-R112 (2011)
    The Ndc80 complex is a key component of the kinetochore–microtubule interface. Two studies now demonstrate that a conserved loop region within the extended coiled-coil of Ndc80 plays an unexpected role in recruiting proteins to the kinetochore.
  • Cell Evolution: Gene Transfer Agents and the Origin of Mitochondria
    - curr biol 21(3):R112-R114 (2011)
    Recently, α-proteobacteria have been shown to possess virus-like gene transfer agents that facilitate high frequency gene transfer in natural environments between distantly related lineages. This system could have driven the genomic integration of the mitochondrial progenitor and its proto-eukaryote host and contributed to the evolutionary mosaic of genes seen in modern-day prokaryotic and eukaryotic genomes.
  • Super-Resolution Microscopy: A New Dimension in Focal Adhesions
    - curr biol 21(3):R115-R116 (2011)
    Super-resolution light microscopy images of integrin-mediated adhesions have revealed that signaling and cytoskeletal proteins reside at characteristic vertical distances between the plasma membrane and F-actin.
  • Animal Cognition: Concepts from Apes to Bees
    - curr biol 21(3):R116-R119 (2011)
    New research shows that honeybees can classify arrangements of two visual patterns according to their spatial configuration. Can bees learn relational concepts of 'above' and 'below'? And are the underlying psychological processes comparable in humans and other primates facing similar tasks?
  • Cytokinesis: Thinking Outside the Cell
    - curr biol 21(3):R119-R121 (2011)
    How might the extracellular matrix contribute to cytokinesis? In a recent report, evidence is presented that the conserved extracellular matrix protein hemicentinHIM-4 is required for cytokinesis in worms and mice.
  • Cell–Cell Fusion: A New Function for Invadosomes
    - curr biol 21(3):R121-R123 (2011)
    Podosomes are cytoskeletal-based structures involved in extracellular matrix remodeling and cellular motility. A new study now implicates podosomes in pore formation during myoblast fusion.
  • Neuroscience: What We Cannot Model, We Do Not Understand
    - curr biol 21(3):R123-R125 (2011)
    To understand computations in neuronal circuits, a model of a small patch of cortex has been developed that can describe the firing regime in the visual system remarkably well.
  • Molecular Regulation of Lumen Morphogenesis
    - curr biol 21(3):R126-R136 (2011)
    The asymmetric polarization of cells allows specialized functions to be performed at discrete subcellular locales. Spatiotemporal coordination of polarization between groups of cells allowed the evolution of metazoa. For instance, coordinated apical-basal polarization of epithelial and endothelial cells allows transport of nutrients and metabolites across cell barriers and tissue microenvironments. The defining feature of such tissues is the presence of a central, interconnected luminal network. Although tubular networks are present in seemingly different organ systems, such as the kidney, lung, and blood vessels, common underlying principles govern their formation. Recent studies using in vivo and in vitro models of lumen formation have shed new light on the molecular networks regulating this fundamental process. We here discuss progress in understanding common design principles underpinning de novo lumen formation and expansion.
  • Cell-to-Cell Variability in PI3K Protein Level Regulates PI3K-AKT Pathway Activity in Cell Populations
    - curr biol 21(3):173-183 (2011)
    Background Cell-to-cell variability in populations has been widely observed in mammalian cells. This heterogeneity can result from random stochastic events or can be deliberately maintained through regulatory processes. In the latter case, heterogeneity should confer a selective advantage that benefits the entire population. Results Using multicolor flow cytometry, we have uncovered robust heterogeneity in phosphoinositide 3-kinase (PI3K) activity in MCF10A cell populations, which had been previously masked by techniques that only measure population averages. We show that AKT activity is bimodal in response to EGF stimulation and correlates with PI3K protein level, such that only cells with high PI3K protein can activate AKT. We further show that heterogeneity in PI3K protein levels is invariably maintained in cell populations through a degradation/resynthesis cycle that can be regulated by cell density. Conclusions Given that the PI3K pathway is one of the most frequently upregulated pathways in cancer, we propose that heterogeneity in PI3K activity is beneficial to normal tissues by restricting PI3K activation to only a subset of cells. This may serve to protect the population as a whole from overactivating the pathway, which can lead to cellular senescence or cancer. Consistent with this, we show that oncogenic mutations in p110α (H1047R and E545K) partially evade this negative regulation, resulting in increased AKT activity in the population.
  • Modeling Vesicle Traffic Reveals Unexpected Consequences for Cdc42p-Mediated Polarity Establishment
    - curr biol 21(3):184-194 (2011)
    Background Polarization in yeast has been proposed to involve a positive feedback loop whereby the polarity regulator Cdc42p orients actin cables, which deliver vesicles carrying Cdc42p to the polarization site. Previous mathematical models treating Cdc42p traffic as a membrane-free flux suggested that directed traffic would polarize Cdc42p, but it remained unclear whether Cdc42p would become polarized without the membrane-free simplifying assumption. Results We present mathematical models that explicitly consider stochastic vesicle traffic via exocytosis and endocytosis, providing several new insights. Our findings suggest that endocytic cargo influences the timing of vesicle internalization in yeast. Moreover, our models provide quantitative support for the view that integral membrane cargo proteins would become polarized by directed vesicle traffic given the experimentally determined rates of vesicle traffic and diffusion. However, such traffic cannot effectively polarize the more rapidly diffusing Cdc42p in the model without making additional assumptions that seem implausible and lack experimental support. Conclusions Our findings suggest that actin-directed vesicle traffic would perturb, rather than reinforce, polarization in yeast.
  • Emotional and Social Behaviors Elicited by Electrical Stimulation of the Insula in the Macaque Monkey
    - curr biol 21(3):195-199 (2011)
    Evidence from a large number of brain imaging studies has shown that, in humans, the insula, and especially its anterior part, is involved in emotions and emotion recognition [[1], [2], [3], [4], [5], [6], [7] and [8]]. Typically, however, these studies revealed that, besides the insula, a variety of other cortical and subcortical areas are also active. Brain imaging studies are correlative in nature, and, as such, they cannot give indications about the necessary contribution of the different centers involved in emotions. In the present study, we aimed to define more clearly the role of the insula in emotional and social behavior of the monkey by stimulating it electrically. Using this technique, one may determine whether direct activation of the insula can produce specific emotional or social behaviors and exactly which parts of this structure are responsible for these behaviors. The results showed that two emotional behaviors, a basic one (disgust) and a social one (! affiliative state), were easily elicited by electrical stimulation of specific parts of the insula. Both behaviors were characterized by specific motor and vegetative responses and by a dramatic change in the monkey's responsiveness to external stimuli.
  • Observers Exploit Stochastic Models of Sensory Change to Help Judge the Passage of Time
    - curr biol 21(3):200-206 (2011)
    Sensory stimulation can systematically bias the perceived passage of time [[1], [2], [3], [4] and [5]], but why and how this happens is mysterious. In this report, we provide evidence that such biases may ultimately derive from an innate and adaptive use of stochastically evolving dynamic stimuli to help refine estimates derived from internal timekeeping mechanisms [[6], [7], [8], [9], [10], [11], [12], [13], [14] and [15]]. A simplified statistical model based on probabilistic expectations of stimulus change derived from the second-order temporal statistics of the natural environment [[16] and [17]] makes three predictions. First, random noise-like stimuli whose statistics violate natural expectations should induce timing bias. Second, a previously unexplored obverse of this effect is that similar noise stimuli with natural statistics should reduce the variability of timing estimates. Finally, this reduction in variability should scale with the interval being timed, s! o as to preserve the overall Weber law of interval timing. All three predictions are borne out experimentally. Thus, in the context of our novel theoretical framework, these results suggest that observers routinely rely on sensory input to augment their sense of the passage of time, through a process of Bayesian inference based on expectations of change in the natural environment.
  • The Ndc80 Loop Region Facilitates Formation of Kinetochore Attachment to the Dynamic Microtubule Plus End
    - curr biol 21(3):207-213 (2011)
    Proper chromosome segregation in mitosis relies on correct kinetochore-microtubule (KT-MT) interactions. The KT initially interacts with the lateral surface of a single MT (lateral attachment) extending from a spindle pole and is subsequently anchored at the plus end of the MT (end-on attachment) [1]. The conversion from lateral to end-on attachment is crucial because end-on attachment is more robust [[2], [3] and [4]] and thought to be necessary to sustain KT-MT attachment when tension is applied across sister KTs upon their biorientation [1]. The mechanism for this conversion is still elusive. The Ndc80 complex is an essential component of the KT-MT interface [[1] and [5]], and here we studied a role of the Ndc80 loop region, a distinct motif looping out from the coiled-coil shaft of the complex [6], in Saccharomyces cerevisiae. With deletions or mutations of the loop region, the lateral KT-MT attachment occurred normally; however, subsequent conversion to end-on att! achment was defective, leading to failure in sister KT biorientation. The Ndc80 loop region was required for Ndc80-Dam1 interaction and KT loading of the Dam1 complex, which in turn supported KT tethering to the dynamic MT plus end [[3] and [7]]. The Ndc80 loop region, therefore, has an important role in the conversion from lateral to end-on attachment, a crucial maturation step of KT-MT interaction.
  • Ndc80 Internal Loop Interacts with Dis1/TOG to Ensure Proper Kinetochore-Spindle Attachment in Fission Yeast
    - curr biol 21(3):214-220 (2011)
    The Ndc80 complex, a conserved outer kinetochore complex, comprising four components (Ndc80/Hec1, Nuf2, Spc24, and Spc25), constitutes one of the core microtubule-binding sites within the kinetochore [[1], [2] and [3]]. Despite this knowledge, molecular mechanisms by which this complex contributes to establishment of correct bipolar attachment of the kinetochore to the spindle microtubule remain largely elusive [[1], [2], [4] and [5]]. Here we show that the conserved internal loop [[6] and [7]] of fission yeast Ndc80 directly binds the Dis1/TOG microtubule-associated protein [[8], [9] and [10]], thereby coupling spindle microtubule dynamics with kinetochore capture. Ndc80 loop mutant proteins fail to recruit Dis1 to kinetochores, imposing unstable attachment and frequent spindle collapse. In these mutants, mitotic progression is halted attributable to spindle assembly checkpoint activation, and chromosomes remain in the vicinity of the spindle poles without congression! . dis1 deletion precisely phenocopies the loop mutants. Intriguingly, forced targeting of Dis1 to the Ndc80 complex rescues loop mutant's defects. We propose that Ndc80 comprises two microtubule-interacting interfaces: the N-terminal region directly binds the microtubule lattice, while the internal loop interacts with the plus end of microtubules via Dis1/TOG. Therefore, our results provide a crucial insight into how the Ndc80 complex establishes stable bipolar attachment to the spindle microtubule.
  • Visual Influences on Echo Suppression
    - curr biol 21(3):221-225 (2011)
    Locating sounds in realistic scenes is challenging because of distracting echoes and coarse spatial acoustic estimates. Fortunately, listeners can improve performance through several compensatory mechanisms. For instance, their brains perceptually suppress short latency (1–10 ms) echoes by constructing a representation of the acoustic environment in a process called the precedence effect [1]. This remarkable ability depends on the spatial and spectral relationship between the first or precedent sound wave and subsequent echoes [2]. In addition to using acoustics alone, the brain also improves sound localization by incorporating spatially precise visual information. Specifically, vision refines auditory spatial receptive fields [3] and can capture auditory perception such that sound is localized toward a coincident visual stimulus [4]. Although visual cues and the precedence effect are each known to improve performance independently, it is not clear whether these mech! anisms can cooperate or interfere with each other. Here we demonstrate that echo suppression is enhanced when visual information spatially and temporally coincides with the precedent wave. Conversely, echo suppression is inhibited when vision coincides with the echo. These data show that echo suppression is a fundamentally multisensory process in everyday environments, where vision modulates even this largely automatic auditory mechanism to organize a coherent spatial experience.
  • A Southern Hemisphere Bathyal Fauna Is Distributed in Latitudinal Bands
    - curr biol 21(3):226-230 (2011)
    The large-scale spatial distribution of seafloor fauna is still poorly understood. In particular, the bathyal zone has been identified as the key depth stratum requiring further macroecological research [1], particularly in the Southern Hemisphere [2]. Here we analyze a large biological data set derived from 295 research expeditions, across an equator-to-pole sector of the Indian, Pacific, and Southern oceans, to show that the bathyal ophiuroid fauna is distributed in three broad latitudinal bands and not primarily differentiated by oceanic basins as previously assumed. Adjacent faunas form transitional ecoclines rather than biogeographical breaks. This pattern is similar to that in shallow water despite the order-of-magnitude reduction in the variability of environmental parameters at bathyal depths. A reliable biogeography is fundamental to establishing a representative network of marine reserves across the world's oceans [[1] and [3]].
  • A Mechanical Signal Biases Caste Development in a Social Wasp
    - curr biol 21(3):231-235 (2011)
    Understanding the proximate mechanisms of caste development in eusocial taxa can reveal how social species evolved from solitary ancestors [1]. In Polistes wasps, the current paradigm holds that differential amounts of nutrition during the larval stage cause the divergence of worker and gyne (potential queen) castes [2]. But nutrition level alone cannot explain how the first few females to be produced in a colony develop rapidly yet have small body sizes and worker phenotypes [[3] and [4]]. Here, we provide evidence that a mechanical signal biases caste toward a worker phenotype. In Polistes fuscatus, the signal takes the form of antennal drumming (AD), wherein a female trills her antennae synchronously on the rims of nest cells while feeding prey-liquid to larvae [5]. The frequency of AD occurrence is high early in the colony cycle, when larvae destined to become workers are being reared, and low late in the cycle, when gynes are being reared [6]. Subjecting gyne-dest! ined brood to simulated AD-frequency vibrations caused them to emerge as adults with reduced fat stores, a worker trait [7]. This suggests that AD influences the larval developmental trajectory by inhibiting a physiological element that is necessary to trigger diapause, a gyne trait [8].
  • Intertissue Mechanical Stress Affects Frizzled-Mediated Planar Cell Polarity in the Drosophila Notum Epidermis
    - curr biol 21(3):236-242 (2011)
    Frizzled/planar cell polarity (Fz/PCP) signaling controls the orientation of sensory bristles and cellular hairs (trichomes) along the anteroposterior axis of the Drosophila thorax (notum) [[1], [2], [3] and [4]]. A subset of the trichome-producing notum cells differentiate as "tendon cells," serving as attachment sites for the indirect flight muscles (IFMs) to the exoskeleton [5]. Through the analysis of chascon (chas), a gene identified by its ability to disrupt Fz/PCP signaling under overexpression conditions, and jitterbug (jbug)/filamin [6], we show that maintenance of anteroposterior planar polarization requires the notum epithelia to balance mechanical stress generated by the attachment of the IFMs. chas is expressed in notum tendon cells, and its loss of function disturbs cellular orientation at and near the regions where IFMs attach to the epidermis. This effect is independent of the Fz/PCP and fat/dachsous systems [7]. The chas phenotype arises during nor! mal shortening of the IFMs [8] and is suppressed by genetic ablation of the IFMs. chas acts through jbug/filamin and cooperates with MyosinII to modulate the mechanoresponse of notum tendon cells. These observations support the notion that the ability of epithelia to respond to mechanical stress generated by one or more interactions with other tissues during development and organogenesis influences the maintenance of its shape and PCP features.
  • Redox-Responsive Zinc Finger Fidelity Switch in Homing Endonuclease and Intron Promiscuity in Oxidative Stress
    - curr biol 21(3):243-248 (2011)
    It is well understood how mobile introns home to allelic sites, but how they are stimulated to transpose to ectopic locations on an evolutionary timescale is unclear [1]. Here we show that a group I intron can move to degenerate sites under oxidizing conditions. The phage T4 td intron endonuclease, I-TevI, is responsible for this infidelity. We demonstrate that I-TevI, which promotes mobility and is subject to autorepression [2] and translational control [3], is also regulated posttranslationally by a redox mechanism. Redox regulation is exercised by a zinc finger (ZF) in a linker that connects the catalytic domain of I-TevI to the DNA binding domain. Four cysteines coordinate Zn2+ in the ZF, which ensures that I-TevI cleaves its DNA substrate at a fixed distance, 23–25 nucleotides upstream of the intron insertion site [4]. We show that the fidelity of I-TevI cleavage is controlled by redox-responsive Zn2+ cycling. When the ZF is mutated, or after exposure of the wil! d-type I-TevI to H2O2, intron homing to degenerate sites is increased, likely because of indiscriminate DNA cleavage. These results suggest a mechanism for rapid intron dispersal, joining recent descriptions of the activation of biomolecular processes by oxidative stress through cysteine chemistry [[5] and [6]].
  • Representation of Others' Action by Neurons in Monkey Medial Frontal Cortex
    - curr biol 21(3):249-253 (2011)
    Successful social interaction depends on not only the ability to identify with others but also the ability to distinguish between aspects of self and others [[1], [2], [3] and [4]]. Although there is considerable knowledge of a shared neural substrate between self-action and others' action [5], it remains unknown where and how in the brain the action of others is uniquely represented. Exploring such agent-specific neural codes is important because one's action and intention can differ between individuals [1]. Moreover, the assignment of social agency breaks down in a range of mental disorders [[6], [7] and [8]]. Here, using two monkeys monitoring each other's action for adaptive behavioral planning, we show that the medial frontal cortex (MFC) contains a group of neurons that selectively encode others' action. These neurons, observed in both dominant and submissive monkeys, were significantly more prevalent in the dorsomedial convexity region of the MFC including the p! re-supplementary motor area than in the cingulate sulcus region of the MFC including the rostral cingulate motor area. Further tests revealed that the difference in neuronal activity was not due to gaze direction or muscular activity. We suggest that the MFC is involved in self-other differentiation in the domain of motor action and provides a fundamental neural signal for social learning.
  • Visual Crowding Is Correlated with Awareness
    - curr biol 21(3):254-258 (2011)
    Crowding by nearby features causes identification failures in the peripheral visual field [[1] and [2]]. However, prominent visual features can sometimes fail to reach awareness [[3] and [4]], causing scenes to be incorrectly interpreted. Here we examine whether awareness of the flanking features is necessary for crowding to occur. Flankers that were physically present were rendered perceptually absent with adaptation-induced blindness [5]. In a letter identification task, targets were presented unflanked or with up to four flanker letters. On each trial, observers reported both the number of letters they perceived and the identity of a target letter. This paradigm allowed trial-by-trial assessment of awareness and crowding and ensured that both targets and flankers were attended. Target-letter identification performance was correlated with the number of flanking letters that were perceived on a given trial, regardless of the number that were physically present. Our da! ta demonstrate that crowding can be released when flanking elements at attended locations are suppressed from visual awareness.

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