Current Biology

Imaging of Transgenic Cricket Embryos Reveals Cell Movements Consistent with a Syncytial Patterning Mechanism.

Publication Date: 2010 Aug 25 PMID: 20800488
Authors: Nakamura, T. - Yoshizaki, M. - Ogawa, S. - Okamoto, H. - Shinmyo, Y. - Bando, T. - Ohuchi, H. - Noji, S. - Mito, T.
Journal: Curr Biol

The mode of insect embryogenesis varies among species, reflecting adaptations to different life history strategies [1, 2]. In holometabolous insects, which include the model systems, such as the fruit fly and the red flour beetle, a large proportion of the blastoderm produces an embryo, whereas hemimetabolous embryos generally arise from a small region of the blastoderm [3]. Despite their importance in evolutionary studies, information of early developmental dynamics of hemimetabolous insects remains limited. Here, to clarify how maternal and gap gene products act in patterning the embryo of basal hemimetabolous insects, we analyzed the dynamic segmentation process in transgenic embryos of an intermediate-germ insect species, the cricket, Gryllus bimaculatus. Our data based on live imaging of fluorescently labeled embryonic cells and nuclei suggest that the positional specification of the cellular blastoderm may be established in the syncytium, where maternally derived gradients could act fundamentally in a way that is similar to that of Drosophila, namely throughout the egg. Then, the blastoderm cells move dynamically, retaining their positional information to form the posteriorly localized germ anlage. Furthermore, we find that the anterior head region of the cricket embryo is specified by orthodenticle in a cellular environment earlier than the gnathal and thoracic regions. Our findings imply that the syncytial mode of the early segmentation in long-germ insects evolved from a dynamic syncytial-to-cellular mode found in the present study, accompanied by a heterochronic shift of gap gene action.

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Shadow Enhancers Foster Robustness of Drosophila Gastrulation.

Publication Date: 2010 Aug 25 PMID: 20797865
Authors: Perry, M. W. - Boettiger, A. N. - Bothma, J. P. - Levine, M.
Journal: Curr Biol

Critical developmental control genes sometimes contain "shadow" enhancers that can be located in remote positions, including the introns of neighboring genes [1]. They nonetheless produce patterns of gene expression that are the same as or similar to those produced by more proximal primary enhancers. It was suggested that shadow enhancers help foster robustness in gene expression in response to environmental or genetic perturbations [2, 3]. We critically tested this hypothesis by employing a combination of bacterial artificial chromosome (BAC) recombineering and quantitative confocal imaging methods [2, 4]. Evidence is presented that the snail gene is regulated by a distal shadow enhancer located within a neighboring locus. Removal of the proximal primary enhancer does not significantly perturb snail function, including the repression of neurogenic genes and formation of the ventral furrow during gastrulation at normal temperatures. However, at elevated temperatures, there is sporadic loss of snail expression and coincident disruptions in gastrulation. Similar defects are observed at normal temperatures upon reductions in the levels of Dorsal, a key activator of snail expression (reviewed in [5]). These results suggest that shadow enhancers represent a novel mechanism of canalization whereby complex developmental processes "bring about one definite end-result regardless of minor variations in conditions" [6].

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Mitotic Kinesin CENP-E Promotes Microtubule Plus-End Elongation.

Publication Date: 2010 Aug 25 PMID: 20797864
Authors: Sardar, H. S. - Luczak, V. G. - Lopez, M. M. - Lister, B. C. - Gilbert, S. P.
Journal: Curr Biol

Centromere protein CENP-E is a dimeric kinesin (Kinesin-7 family) with critical roles in mitosis, including establishment of microtubule (MT)-chromosome linkage and movement of mono-oriented chromosomes on kinetochore microtubules for proper alignment at metaphase [1-9]. We performed studies to test the hypothesis that CENP-E promotes MT elongation at the MT plus ends. A human CENP-E construct was engineered, expressed, and purified, and it yielded the CENP-E-6His dimeric motor protein. The results show that CENP-E promotes MT plus-end-directed MT gliding at 11 nm/s. The results from real-time microscopy assays indicate that 60.3% of polarity-marked MTs exhibited CENP-E-promoted MT plus-end elongation. The MT extension required ATP turnover, and MT plus-end elongation occurred at 1.48 mum/30 min. Immunolocalization studies revealed that 80.8% of plus-end-elongated MTs showed CENP-E at the MT plus end. The time dependence of CENP-E-promoted MT elongation in solution best fit a single exponential function (k(obs) = 5.1 s(-1)), which is indicative of a mechanism in which alpha,beta-tubulin subunit addition is tightly coupled to ATP turnover. Based on these results, we propose that CENP-E, as part of its function in chromosome kinetochore-MT linkage, plays a direct role in MT elongation.

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Drosophila TRPA1 Channel Is Required to Avoid the Naturally Occurring Insect Repellent Citronellal.

Publication Date: 2010 Aug 30 PMID: 20797863
Authors: Kwon, Y. - Kim, S. H. - Ronderos, D. S. - Lee, Y. - Akitake, B. - Woodward, O. M. - Guggino, W. B. - Smith, D. P. - Montell, C.
Journal: Curr Biol

Plants produce insect repellents, such as citronellal, which is the main component of citronellal oil. However, the molecular pathways through which insects sense botanical repellents are unknown. Here, we show that Drosophila use two pathways for direct avoidance of citronellal. The olfactory coreceptor OR83b contributes to citronellal repulsion and is essential for citronellal-evoked action potentials. Mutations affecting the Ca(2+)-permeable cation channel TRPA1 result in a comparable defect in avoiding citronellal vapor. The TRPA1-dependent aversion to citronellal relies on a G protein (Gq)/phospholipase C (PLC) signaling cascade rather than direct detection of citronellal by TRPA1. Loss of TRPA1, Gq, or PLC causes an increase in the frequency of citronellal-evoked action potentials in olfactory receptor neurons. Absence of the Ca(2+)-activated K(+) channel (BK channel) Slowpoke results in a similar impairment in citronellal avoidance and an increase in the frequency of action potentials. These results suggest that TRPA1 is required for activation of a BK channel to modulate citronellal-evoked action potentials and for aversion to citronellal. In contrast to Drosophila TRPA1, Anopheles gambiae TRPA1 is directly and potently activated by citronellal, thereby raising the possibility that mosquito TRPA1 may be a target for developing improved repellents to reduce insect-borne diseases such as malaria.

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The Mon1-Ccz1 Complex Is the GEF of the Late Endosomal Rab7 Homolog Ypt7.

Publication Date: 2010 Aug 25 PMID: 20797862
Authors: Nordmann, M. - Cabrera, M. - Perz, A. - Brocker, C. - Ostrowicz, C. - Engelbrecht-Vandre, S. - Ungermann, C.
Journal: Curr Biol

Rab GTPases coordinate membrane fusion reactions [1]. Rab-GDP requires a guanine nucleotide exchange factor (GEF) for its conversion to the active GTP form. It then binds to effectors such as multimeric tethering complexes and supports fusion [2]. GTPase-activating proteins (GAPs) promote GTP hydrolysis to inactivate the Rab. GEFs are thus critical activators of fusion reactions [3, 4]. The Rab GEF family is diverse, ranging from multimeric complexes [5] to monomeric GEFs [6-9]. At the late endosome, Rab7 activation is critical for endosomal maturation. The yeast Rab7 homolog Ypt7 binds to the homotypic fusion and protein sorting (HOPS) complex [10, 11]. Its subunit Vps39/Vam6 has been proposed as a GEF for Ypt7 [12] and the Rag GTPase Gtr1 [13], but other genetic evidence has implicated the endosomal protein Ccz1 as a GEF for Ypt7 [14]. Ccz1 and its binding partner Mon1 have been linked to endosomal transport and maturation [15-20]. We now provide evidence that the dimeric Mon1-Ccz1 complex is the Rab7/Ypt7 GEF. The Mon1-Ccz1 complex, but neither protein alone, counteracts GAP function in vivo, rescues in vitro fusion of vacuoles carrying Ypt7-GDP, and promotes nucleotide exchange on Ypt7 independently of Vps39/HOPS. Our data indicate that the Mon1-Ccz1 complex triggers endosomal maturation by activating Ypt7 on late endosomes.

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Hos1 Is a Lysine Deacetylase for the Smc3 Subunit of Cohesin.

Publication Date: 2010 Aug 25 PMID: 20797861
Authors: Xiong, B. - Lu, S. - Gerton, J. L.
Journal: Curr Biol

Chromosome cohesion is a cell-cycle-regulated process in which sister chromatids are held together from the time of replication until the time of separation at the metaphase-to-anaphase transition, ensuring accurate chromosome segregation [1-9]. Chromosome cohesion is established during S phase, and this process requires the four subunits of the cohesin complex (Smc1, Smc3, Mcd1/Scc1, and Irr1/Scc3) and the acetyltransferase Eco1 [10-13]. Acetylation of Smc3 by Eco1 at two evolutionarily conserved lysine residues promotes cohesion establishment during S phase in budding yeast and humans [14-16]. Here we report that Hos1, a member of the evolutionarily conserved class I histone deacetylase family, acts as a deacetylase for Smc3 in S. cerevisiae. We examine the Smc3 acetylation level in nine histone deacetylase deletion strains and find that the acetylation level is increased specifically in a hos1Delta strain post-S phase. Coimmunoprecipitation experiments show that Hos1 interacts with Smc3 and that the interaction is most pronounced as cells reach anaphase. We provide direct evidence that Hos1 can deacetylate Smc3 and retains a soluble pool of deacetylated Smc3. Overexpression of Hos1 results in less acetylation of Smc3 and cohesion defects in both WT and eco1 mutant strains; mutation of the Hos1 active site abolishes the defects. Hos1 may help to maintain a pool of unacetylated Smc3 that can be used for new chromosome cohesion.

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Social learning: the importance of copying others.

Publication Date: 2010 Aug 24 PMID: 20728057
Authors: Gruter, C. - Leadbeater, E. - Ratnieks, F. L.
Journal: Curr Biol

A new study argues that social learning is adaptive because 'demonstrators' inadvertently filter information, so that copiers learn behaviours that have proved successful. There are remarkable parallels between these findings and data on how social insects share information about food locations.

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Plant fertilization: bursting pollen tubes!

Publication Date: 2010 Aug 24 PMID: 20728056
Authors: Franklin-Tong, N.
Journal: Curr Biol

Higher plants don't have motile sperm; they rely on pollen tubes to deliver them. Recent research has identified key components involved in pollen tube tip bursting that allow sperm release and fertilization.

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Neurophysiology: recording from neurons in action.

Publication Date: 2010 Aug 24 PMID: 20728055
Authors: Borst, A.
Journal: Curr Biol

Sensory neurons have mostly been studied in fixed animals, but how do they behave when the animal is free to move? A recent study shows that, during locomotor activity, besides there being a general enhancement in responsiveness, the tuning curves of neurons can also change, altering their optimal stimuli.

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Bacterial invasion: entry through the exocyst door.

Publication Date: 2010 Aug 24 PMID: 20728054
Authors: Braun, V. - Brumell, J. H.
Journal: Curr Biol

Salmonella entry into host cells involves rearrangements of actin and mobilization of membranes. Here we discuss new findings showing that Salmonella recruits the exocyst complex, which plays a role in vesicle secretion, to the site of invasion to promote its entry.

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Synthetic biology: now that we're creators, what should we create?

Publication Date: 2010 Aug 24 PMID: 20728053
Authors: Cohan, F. M.
Journal: Curr Biol

A 'synthetic' microbe has been created by introducing the artificially produced genome of one species into the cytoplasm of another. The technology allows the introduction of easily transferable adaptive units, as well as sets of genes that have likely never been transferred successfully.

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Neuronal morphogenesis: worms get an EFF in dendritic arborization.

Publication Date: 2010 Aug 24 PMID: 20728052
Authors: Shrestha, B. R. - Grueber, W. B.
Journal: Curr Biol

The development of neuronal dendritic trees involves positive and negative control of growth and branching, as well as modulation of the spacing and orientation of branches. A new study reveals the importance of a membrane fusogen in the dendrite arborization of a pair of highly-branched worm sensory neurons.

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Sexual selection: the weevils of inbreeding.

Publication Date: 2010 Aug 24 PMID: 20728051
Authors: Booksmythe, I. - Kokko, H. - Jennions, M. D.
Journal: Curr Biol

A recent study has used inbreeding depression to gain insight into the maintenance of additive genetic variation in populations, with intriguing implications for good genes models of sexual selection.

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Cell-matrix adhesion: slip and immobilization under force.

Publication Date: 2010 Aug 24 PMID: 20728050
Authors: Verkhovsky, A. B.
Journal: Curr Biol

When force is applied to cell-matrix adhesion complexes, they respond by growing larger and stronger. It emerges that strengthening involves transient motion of the transmembrane integrin receptors and their eventual immobilization to the extracellular matrix.

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Biomechanics: an army marching with its stomach.

Publication Date: 2010 Aug 24 PMID: 20728049
Authors: Sutton, G. P.
Journal: Curr Biol

A novel X-ray technique shows that the internal organs of crawling caterpillars slide past the body walls like pistons in a new kind of legged locomotion.

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Tudor domain.

Publication Date: 2010 Aug 24 PMID: 20728048
Authors: Lasko, P.
Journal: Curr Biol

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Visual filling-in.

Publication Date: 2010 Aug 24 PMID: 20728047
Authors: Anstis, S.
Journal: Curr Biol

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Visual Control of Altitude in Flying Drosophila.

Publication Date: 2010 Aug 18 PMID: 20727759
Authors: Straw, A. D. - Lee, S. - Dickinson, M. H.
Journal: Curr Biol

Unlike creatures that walk, flying animals need to control their horizontal motion as well as their height above the ground. Research on insects, the first animals to evolve flight, has revealed several visual reflexes that are used to govern horizontal course. For example, insects orient toward prominent vertical features in their environment [1-5] and generate compensatory reactions to both rotations [6, 7] and translations [1, 8-11] of the visual world. Insects also avoid impending collisions by veering away from visual expansion [9, 12-14]. In contrast to this extensive understanding of the visual reflexes that regulate horizontal course, the sensory-motor mechanisms that animals use to control altitude are poorly understood. Using a 3D virtual reality environment, we found that Drosophila utilize three reflexes-edge tracking, wide-field stabilization, and expansion avoidance-to control altitude. By implementing a dynamic visual clamp, we found that flies do not regulate altitude by maintaining a fixed value of optic flow beneath them, as suggested by a recent model [15]. The results identify a means by which insects determine their absolute height above the ground and uncover a remarkable correspondence between the sensory-motor algorithms used to regulate motion in the horizontal and vertical domains.

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Warts and Yorkie Mediate Intestinal Regeneration by Influencing Stem Cell Proliferation.

Publication Date: 2010 Aug 18 PMID: 20727758
Authors: Staley, B. K. - Irvine, K. D.
Journal: Curr Biol

Homeostasis in the Drosophila midgut is maintained by stem cells [1, 2]. The intestinal epithelium contains two types of differentiated cells that are lost and replenished: enteroendocrine (EE) cells and enterocytes (ECs). Intestinal stem cells (ISCs) are the only cells in the adult midgut that proliferate [3, 4], and ISC divisions give rise to an ISC and an enteroblast (EB), which differentiates into an EC or an EE cell [3-5]. If the midgut epithelium is damaged, then ISC proliferation increases [6-12]. Damaged ECs express secreted ligands (Unpaired proteins) that activate Jak-Stat signaling in ISCs and EBs to promote their proliferation and differentiation [7, 9, 13, 14]. We show that the Hippo pathway components Warts and Yorkie mediate a transition from low- to high-level ISC proliferation to facilitate regeneration. The Hippo pathway regulates growth in diverse organisms and has been linked to cancer [15, 16]. Yorkie is activated in ECs in response to tissue damage or activation of the damage-sensing Jnk pathway. Activation of Yorkie promotes expression of unpaired genes and triggers a nonautonomous increase in ISC proliferation. Our observations uncover a role for Hippo pathway components in regulating stem cell proliferation and intestinal regeneration.

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Human Parietal Cortex Structure Predicts Individual Differences in Perceptual Rivalry.

Publication Date: 2010 Aug 18 PMID: 20727757
Authors: Kanai, R. - Bahrami, B. - Rees, G.
Journal: Curr Biol

When visual input has conflicting interpretations, conscious perception can alternate spontaneously between competing interpretations [1]. There is a large amount of unexplained variability between individuals in the rate of such spontaneous alternations in perception [2-5]. We hypothesized that variability in perceptual rivalry might be reflected in individual differences in brain structure, because brain structure can exhibit systematic relationships with an individual's cognitive experiences and skills [6-9]. To test this notion, we examined in a large group of individuals how cortical thickness, local gray-matter density, and local white-matter integrity correlate with individuals' alternation rate for a bistable, rotating structure-from-motion stimulus [10]. All of these macroscopic measures of brain structure consistently revealed that the structure of bilateral superior parietal lobes (SPL) could account for interindividual variability in perceptual alternation rate. Furthermore, we examined whether the bilateral SPL regions play a causal role in the rate of perceptual alternations by using transcranial magnetic stimulation (TMS) and found that transient disruption of these areas indeed decreases the rate of perceptual alternations. These findings demonstrate a direct relationship between structure of SPL and individuals' perceptual switch rate.

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Social Punishment of Dishonest Signalers Caused by Mismatch between Signal and Behavior.

Publication Date: 2010 Aug 18 PMID: 20727756
Authors: Tibbetts, E. A. - Izzo, A.
Journal: Curr Biol

Many animals use conventional signals of fighting ability to mediate aggressive conflict. Given the apparent benefits of signaling inaccurately high fighting ability, there is extensive interest in why animals communicate their abilities honestly [1]. One hypothesis is that inaccurate signalers receive social punishment that disfavors inaccuracy. Although the idea that social punishment can prevent dishonesty is appealing, questions about the evolutionary stability of this hypothesis remain [2]. For example, how do individuals know a rival is cheating? We independently manipulated a signal of fighting ability and agonistic behavior in Polistes dominulus wasps to test the behavioral mechanisms underlying social punishment. Remarkably, a mismatch between signal and behavior caused social punishment. Individuals with experimentally altered signals received more aggression from rivals. Individuals with experimentally altered behavior were less able to establish dominance relationships. In contrast, control individuals and those with experimentally altered signal and behavior suffered neither cost. They received little aggression and established stable dominance relationships. Therefore, individuals use information about the match between signal and behavior to assess the accuracy of rival signals. A mismatch produces costly social interactions. This simple behavioral mechanism provides a clear cost to signal inaccuracy that may maintain honest communication over evolutionary time.

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An Aerial-Hawking Bat Uses Stealth Echolocation to Counter Moth Hearing.

Publication Date: 2010 Aug 18 PMID: 20727755
Authors: Goerlitz, H. R. - Ter Hofstede, H. M. - Zeale, M. R. - Jones, G. - Holderied, M. W.
Journal: Curr Biol

Ears evolved in many nocturnal insects, including some moths, to detect bat echolocation calls and evade capture [1, 2]. Although there is evidence that some bats emit echolocation calls that are inconspicuous to eared moths, it is difficult to determine whether this was an adaptation to moth hearing or originally evolved for a different purpose [2, 3]. Aerial-hawking bats generally emit high-amplitude echolocation calls to maximize detection range [4, 5]. Here we present the first example of an echolocation counterstrategy to overcome prey hearing at the cost of reduced detection distance. We combined comparative bat flight-path tracking and moth neurophysiology with fecal DNA analysis to show that the barbastelle, Barbastella barbastellus, emits calls that are 10 to 100 times lower in amplitude than those of other aerial-hawking bats, remains undetected by moths until close, and captures mainly eared moths. Model calculations demonstrate that only bats emitting such low-amplitude calls hear moth echoes before their calls are conspicuous to moths. This stealth echolocation allows the barbastelle to exploit food resources that are difficult to catch for other aerial-hawking bats emitting calls of greater amplitude.

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Q&A: Elizabeth C. Raff.

Publication Date: 2010 Aug 10 PMID: 20705542
Authors: Raff, E. C.
Journal: Curr Biol

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Panama's frog decline.

Publication Date: 2010 Aug 10 PMID: 20705541
Authors: Williams, N.
Journal: Curr Biol

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Local moulding.

Publication Date: 2010 Aug 10 PMID: 20705540
Authors: Williams, N.
Journal: Curr Biol

New studies suggest the extent to which fungi are local to their indoor habitats.

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Arctic reality.

Publication Date: 2010 Aug 10 PMID: 20705539
Authors: Williams, N.
Journal: Curr Biol

The threat to the Hudson Bay polar bears highlights the reality of a changing climate under attack from sceptics.

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Cuts spark university rethink.

Publication Date: 2010 Aug 10 PMID: 20705538
Authors: Gross, M.
Journal: Curr Biol

Britain's new government is thinking aloud about radical changes to university funding and other countries are also considering the future.

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Population in the spotlight.

Publication Date: 2010 Aug 10 PMID: 20705537
Authors: Williams, N.
Journal: Curr Biol

A new inquiry hopes to highlight the issue of population, ignored by most politicians.

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Gulf braced for the big clean-up.

Publication Date: 2010 Aug 10 PMID: 20705536
Authors: Williams, N.
Journal: Curr Biol

Earlier oil spills suggest the Gulf may be in for the long haul to recover from this year's disaster.

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Differential regulation of unconventional fission yeast myosins via the actin track.

Publication Date: 2010 Aug 24 PMID: 20705471
Authors: Clayton, J. E. - Sammons, M. R. - Stark, B. C. - Hodges, A. R. - Lord, M.
Journal: Curr Biol

BACKGROUND: Fission yeast possesses three unconventional myosins: Myo1p (a class I myosin that functions at endocytic actin patches) and Myo51p and Myo52p (class V myosins that function at contractile rings and actin cables, respectively). Here we used a combination of in vivo and in vitro approaches to investigate how changes in the actin track influence the motor activity and spatial regulation of these myosins. RESULTS: We optimized the isolation of Myo1p, Myo51p, and Myo52p. All three myosins exhibited robust motor activity in ATPase and actin filament gliding assays. However, decoration of actin with tropomyosin differentially regulates the activity of these motors. Tropomyosin inhibits Myo1p by blocking its ability to form productive associations with actin filaments, whereas tropomyosin increases the actin affinity and ATPase activity of Myo51p and Myo52p. The actin filament crosslinking protein fimbrin rescues Myo1p motor activity by displacing tropomyosin from actin filaments. Consistent with our in vitro findings, fimbrin and tropomyosin have opposing effects on Myo1p function at actin patches. Defects in tropomyosin function led to shorter Myo1p patch lifetimes, whereas loss of fimbrin extended Myo1p lifetimes. Furthermore, defects in tropomyosin function decreased the efficiency of Myo52p-directed motility along actin cables in the cell. CONCLUSION: Tropomyosin promotes myosin-V motility along actin cables. Accumulation of fimbrin at actin patches relieves Myo1p from tropomyosin-mediated inhibition, ensuring maximal myosin-I motor activity at these sites. Thus, spatial regulation of myosin motor function is in part controlled by specific changes in the composition of the actin track.

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Membrane Thickness Cue for Cold Sensing in a Bacterium.

Publication Date: 2010 Aug 12 PMID: 20705470
Authors: Cybulski, L. E. - Martin, M. - Mansilla, M. C. - Fernandez, A. - de Mendoza, D.
Journal: Curr Biol

Thermosensors are ubiquitous integral membrane proteins found in all kinds of life. They are involved in many physiological roles, including membrane remodeling, chemotaxis, touch, and pain [1-3], but, the mechanism by which their transmembrane (TM) domains transmit temperature signals is largely unknown. The histidine kinase DesK from Bacillus subtilis is the paradigmatic example of a membrane-bound thermosensor suited to remodel membrane fluidity when the temperature drops below approximately 30 degrees C [1, 4] providing, thus, a tractable system for investigating the mechanism of TM-mediated input-output control of thermal adaptation. Here we show that the multimembrane-spanning domain from DesK can be simplified into a chimerical single-membrane-spanning minimal sensor (MS) that fully retains, in vivo and in vitro, the sensing properties of the parental system. The MS N terminus contains three hydrophilic amino acids near the lipid-water interface creating an instability hot spot. Mutational analysis of this boundary-sensitive beacon revealed that membrane thickness controls the signaling state of the sensor by dictating the hydration level of the metastable hydrophilic spot. Guided by these results we biochemically demonstrated that the MS signal transmission activity is sensitive to bilayer thickness. Membrane thickness could be a general cue for sensing temperature in many organisms.

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Evolution of a Behavioral Shift Mediated by Superficial Neuromasts Helps Cavefish Find Food in Darkness.

Publication Date: 2010 Aug 11 PMID: 20705469
Authors: Yoshizawa, M. - Goricki, S. - Soares, D. - Jeffery, W. R.
Journal: Curr Biol

How cave animals adapt to life in darkness is a poorly understood aspect of evolutionary biology [1]. Here we identify a behavioral shift and its morphological basis in Astyanax mexicanus, a teleost with a sighted surface-dwelling form (surface fish) and various blind cave-dwelling forms (cavefish) [2-4]. Vibration attraction behavior (VAB) is the ability of fish to swim toward the source of a water disturbance in darkness. VAB was typically seen in cavefish, rarely in surface fish, and was advantageous for feeding success in the dark. The potential for showing VAB has a genetic component and is linked to the mechanosensory function of the lateral line. VAB was evoked by vibration stimuli peaking at 35 Hz, blocked by lateral line inhibitors, first detected after developmental increases in superficial neuromast (SN) number and size [5-7], and significantly reduced by bilateral ablation of SN. We conclude that VAB and SN enhancement coevolved to compensate for loss of vision and to help blind cavefish find food in darkness.

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SPATULA links daytime temperature and plant growth rate.

Publication Date: 2010 Aug 24 PMID: 20705468
Authors: Sidaway-Lee, K. - Josse, E. M. - Brown, A. - Gan, Y. - Halliday, K. J. - Graham, I. A. - Penfield, S.
Journal: Curr Biol

Plants exhibit a wide variety of growth rates that are known to be determined by genetic and environmental factors, and different plants grow optimally at different temperatures, indicating that this is a genetically determined character. Moderate decreases in ambient temperature inhibit vegetative growth, but the mechanism is poorly understood, although a decrease in gibberellin (GA) levels is known to be required. Here we demonstrate that the basic helix-loop-helix transcription factor SPATULA (SPT), previously known to be a regulator of low temperature-responsive germination, mediates the repression of growth by cool daytime temperatures but has little or no growth-regulating role under warmer conditions. We show that only daytime temperatures affect vegetative growth and that SPT couples morning temperature to growth rate. In seedlings, warm temperatures inhibit the accumulation of the SPT protein, and SPT autoregulates its own transcript abundance in conjunction with diurnal effects. Genetic data show that repression of growth by SPT is independent of GA signaling and phytochrome B, as previously shown for PIF4. Our data suggest that SPT integrates time of day and temperature signaling to control vegetative growth rate.

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Dosage compensation and demasculinization of X chromosomes in Drosophila.

Publication Date: 2010 Aug 24 PMID: 20705467
Authors: Bachtrog, D. - Toda, N. R. - Lockton, S.
Journal: Curr Biol

The X chromosome of Drosophila shows a deficiency of genes with male-biased expression, whereas mammalian X chromosomes are enriched for spermatogenesis genes expressed premeiosis and multicopy testis genes. Meiotic X-inactivation and sexual antagonism can only partly account for these patterns. Here, we show that dosage compensation (DC) in Drosophila may contribute substantially to the depletion of male genes on the X. To equalize expression between X-linked and autosomal genes in the two sexes, male Drosophila hypertranscribe their single X, whereas female mammals silence one of their two X chromosomes. We combine fine-scale mapping data of dosage compensated regions with genome-wide expression profiles and show that most male-biased genes on the D. melanogaster X are located outside dosage compensated regions. Additionally, X-linked genes that have newly acquired male-biased expression in D. melanogaster are less likely to be dosage compensated, and parental X-linked genes that gave rise to an autosomal male-biased retrocopy are more likely located within compensated regions. This suggests that DC contributes to the observed demasculinization of X chromosomes in Drosophila, both by limiting the emergence of male-biased expression patterns of existing X genes, and by contributing to gene trafficking of male genes off the X.

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Fimbrin and tropomyosin competition regulates endocytosis and cytokinesis kinetics in fission yeast.

Publication Date: 2010 Aug 24 PMID: 20705466
Authors: Skau, C. T. - Kovar, D. R.
Journal: Curr Biol

BACKGROUND: Tropomyosin is an important actin filament-stabilizing protein that controls the access of other essential proteins to filaments, including myosin motors, Arp2/3 complex, formin, and cofilin. It is therefore critical to establish mechanisms for regulating the actin filament binding of tropomyosin. We examined how the actin filament crosslinking protein fimbrin Fim1p and tropomyosin Cdc8p affect each other's ability to bind filaments, localize to particular cellular structures, and regulate filament severing by cofilin Adf1p in fission yeast Schizosaccharomyces pombe. RESULTS: We discovered a novel mechanism for regulating actin filament dynamics in fission yeast. Fim1p inhibits Cdc8p binding to actin filaments in vitro, which permits Adf1p-mediated severing in the presence of Cdc8p. In cells, the balance between Fim1p and Cdc8p is important for both endocytic actin patch kinetics and contractile ring assembly during cytokinesis. High Fim1p concentrations prevent Cdc8p from associating with actin patches, allowing rapid patch turnover and motility. In the absence of Fim1p, ectopic localization of Cdc8p to actin patches increases patch lifetime while decreasing patch motility. Fim1p and Cdc8p also play antagonistic roles during cytokinesis, in which the deletion of Fim1p rescues the contractile ring assembly defects caused by mutation of Cdc8p. CONCLUSION: Fimbrin Fim1p dissociates tropomyosin Cdc8p from actin filaments, permitting cofilin Adf1p-mediated severing. Therefore, we propose that in addition to actin filament crosslinking, Fim1p has a novel role as a positive actin-binding "selector" protein that promotes the access of other proteins to actin filaments by inhibiting Cdc8p.

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Enslavement in the Water Body by Toxic Aphanizomenon ovalisporum, Inducing Alkaline Phosphatase in Phytoplanktons.

Publication Date: 2010 Aug 11 PMID: 20705465
Authors: Bar-Yosef, Y. - Sukenik, A. - Hadas, O. - Viner-Mozzini, Y. - Kaplan, A.
Journal: Curr Biol

The hepatotoxin cylindrospermopsin (CYN) produced by certain cyanobacteria, including Aphanizomenon ovalisporum (hereafter Aphanizomenon) [1], seriously affects lake water quality [2], but its biological role is not known. Strong correlation between Aphanizomenon abundance in Lake Kinneret, Israel, and alkaline phosphatase (APase) activity suggests that inorganic phosphate (Pi) limitation induces the PHO regulon and APase secretion [3]. Staining lake samples with DAPI [4] revealed a high level of polyphosphate bodies (PPB) in Aphanizomenon. Application of enzyme-labeled fluorescence (ELF-APase) [5] showed APase in various organisms, but not in Aphanizomenon. ELF-APase signals and extracellular APase activity in Aphanizomenon were detected only after exploiting PPB under prolonged Pi deprivation in cultures or toward the end of its autumn bloom. Pi deprivation of Aphanizomenon induces CYN production, high-affinity Pi uptake, and an internal, not external, APase. Addition of Aphanizomenon spent media or CYN to various phytoplanktons, including Chlamydomonas reinhardtii, induced genes typically upregulated under Pi limitation and a rise in extracellular APase activity, despite ample surrounding Pi. Coculturing Aphanizomenon with Chlamydomonas or with Debarya sp. showed positive ELF-APase signals, but not in Aphanizomenon. CYN producers promote Pi supply by inducing APase secretion by other phytoplanktons, possibly explaining their increased abundance despite reduced Pi supply from watersheds.

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Cytoskeletal cross-linking and bundling in motor-independent contraction.

Publication Date: 2010 Aug 10 PMID: 20692617
Authors: Sun, S. X. - Walcott, S. - Wolgemuth, C. W.
Journal: Curr Biol

Eukaryotic and prokaryotic cells use cytoskeletal proteins to regulate and modify cell shape. During cytokinesis or eukaryotic cell crawling, contractile forces are generated inside the cell to constrict the division site or to haul the rear of the cell forward, respectively. In many cases, these forces have been attributed to the activity of molecular motors, such as myosin II, which, by pulling on actin filaments, can produce contraction of the actin cytoskeleton. However, prokaryotic division is driven by the tubulin-like protein FtsZ and does not seem to require additional molecular motors to constrict the division site. Likewise, Dictyostelium discoideum and Saccharomyces cerevisiae can perform cytokinesis under motor-free conditions. In addition, many crawling cells can translocate when myosin is inhibited or absent. In this review, we point out another force-generation mechanism that can play a significant role in driving these processes in eukaryotes and prokaryotes. This mechanism is mediated by cross-linking and bundling proteins that form effective interactions between cytoskeletal filaments. Some recent studies in this area are reviewed and the physical underpinnings of this force-generation mechanism are explained.

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Cell polarity: keeping worms LeGaL.

Publication Date: 2010 Aug 10 PMID: 20692616
Authors: Prehoda, K. E. - Bowerman, B.
Journal: Curr Biol

The protein Lethal giant larvae (LGL) regulates cell polarity in diverse animal models. Now, an LGL orthologue has been identified in the worm Caenorhabditis elegans and is shown to function redundantly with a worm-specific polarity protein, PAR-2.

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Visual consciousness: the binocular rivalry explosion.

Publication Date: 2010 Aug 10 PMID: 20692615
Authors: Baker, D. H.
Journal: Curr Biol

A new behavioural technique solves a long-standing puzzle of binocular suppression, demonstrating that adapting reciprocal inhibition governs visual sensitivity and raising key questions about visual awareness.

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Sensory learning: rapid extraction of meaning from noise.

Publication Date: 2010 Aug 10 PMID: 20692614
Authors: Seitz, A. R.
Journal: Curr Biol

Recent studies show that humans can rapidly learn to differentiate originally meaningless sounds into long-lasting memories, illustrating the flexibility of sensory processes and raising important questions about how sensory memories are formed.

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Axonal transport: CDKs as traffic signals for motor-ists along the axon?

Publication Date: 2010 Aug 10 PMID: 20692613
Authors: Holzbaur, E.
Journal: Curr Biol

A screen for axonal cargo mislocalization in Caenorhabditis elegans neurons implicates the cyclin-dependent kinases CDK-5 and PCT-1 and the cyclin CCY-1 in the regulation of the microtubule motor cytoplasmic dynein.

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Animal cognition: multi-modal interactions in ant learning.

Publication Date: 2010 Aug 10 PMID: 20692612
Authors: Graham, P. - Philippides, A. - Baddeley, B.
Journal: Curr Biol

A recent study shows that desert ants use a precise behaviour, based on the internal cues of path integration, to facilitate the learning of visual landmark information. This raises fascinating questions about how insects encode familiar terrain.

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Evolutionary genetics: desperate times call for more sex.

Publication Date: 2010 Aug 10 PMID: 20692611
Authors: Zeyl, C.
Journal: Curr Biol

A new study has found that strains of the fungus Aspergillus nidulans produce more of their spores sexually in environments where they are less fit, resembling a hypothesized transitional stage in the evolution of sex.

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Cell cycle: deconstructing tension.

Publication Date: 2010 Aug 10 PMID: 20692610
Authors: Musacchio, A.
Journal: Curr Biol

Prior to anaphase, sister chromatids must be attached to microtubules and under tension, a condition that satisfies the spindle checkpoint. Removal of sister chromatid cohesion is predicted to cause a fall in tension. Two studies shed light on how cells avoid re-activation of the spindle checkpoint when cohesion is lost.

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Primatology: "a faithful friend is the medicine of life".

Publication Date: 2010 Aug 10 PMID: 20692609
Authors: Alberts, S. C.
Journal: Curr Biol

Close, stable social bonds enhance longevity in wild baboons, providing clues about the importance of social bonds in our own evolutionary history.

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Signal transduction: RABGEF1 fingers RAS for ubiquitination.

Publication Date: 2010 Aug 10 PMID: 20692608
Authors: Colicelli, J.
Journal: Curr Biol

RAS proteins conduct signaling from surface receptors to cytoplasmic effectors, and RAS gain-of-function mutations are pervasive in cancer. A new mechanism for RAS signal attenuation with implications for receptor trafficking has been uncovered.

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Mammalian herbivore breath alerts aphids to flee host plant.

Publication Date: 2010 Aug 10 PMID: 20692607
Authors: Gish, M. - Dafni, A. - Inbar, M.
Journal: Curr Biol

Mammalian herbivores profoundly influence plant-dwelling insects [1]. Most studies have focused on the indirect effect of herbivory on insect populations via damage to the host plant [2,3]. Many insects, however, are in danger of being inadvertently ingested during herbivore feeding. Here, we report that pea aphids (Acyrthosiphon pisum) are able to sense the elevated heat and humidity of the breath of an approaching herbivore and thus salvage most of the colony by simultaneously dropping off the plant in large numbers immediately before the plant is eaten. Dropping entails the risk of losing the host plant and becoming desiccated or preyed upon on the ground [4,5], yet pea aphids may sporadically drop when threatened by insect enemies [6]. The immediate mass dropping, however, is an adaptation to the potential destructive impact of mammalian herbivory on the entire aphid colony. The combination of heat and humidity serves as a reliable cue to impending mammalian herbivory, enabling the aphids to avoid unnecessary dropping. No defensive behavior against incidental predation by herbivores has ever been demonstrated. The pea aphids' highly adaptive escape behavior uniquely demonstrates the strength of the selective pressure large mammalian herbivores impose on insect herbivores.

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Spontaneous brain rhythms predict sleep stability in the face of noise.

Publication Date: 2010 Aug 10 PMID: 20692606
Authors: Dang-Vu, T. T. - McKinney, S. M. - Buxton, O. M. - Solet, J. M. - Ellenbogen, J. M.
Journal: Curr Biol

Quality sleep is an essential part of health and well-being. Yet fractured sleep is disturbingly prevalent in our society, partly due to insults from a variety of noises [1]. Common experience suggests that this fragility of sleep is highly variable between people, but it is unclear what mechanisms drive these differences. Here we show that it is possible to predict an individual's ability to maintain sleep in the face of sound using spontaneous brain rhythms from electroencephalography (EEG). The sleep spindle is a thalamocortical rhythm manifested on the EEG as a brief 11-15 Hz oscillation and is thought to be capable of modulating the influence of external stimuli [2]. Its rate of occurrence, while variable across people, is stable across nights [3]. We found that individuals who generated more sleep spindles during a quiet night of sleep went on to exhibit higher tolerance for noise during a subsequent, noisy night of sleep. This result shows that the sleeping brain's spontaneous activity heralds individual resilience to disruptive stimuli. Our finding sets the stage for future studies that attempt to augment spindle production to enhance sleep continuity when confronted with noise.

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Spider monkeys.

Publication Date: 2010 Aug 10 PMID: 20692605
Authors: Aureli, F. - Schaffner, C. M.
Journal: Curr Biol

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Mosquito-specialist spiders.

Publication Date: 2010 Aug 10 PMID: 20692604
Authors: Cross, F. R. - Jackson, R. R.
Journal: Curr Biol

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Bicaudal-D regulates fragile X mental retardation protein levels, motility, and function during neuronal morphogenesis.

Publication Date: 2010 Aug 24 PMID: 20691595
Authors: Bianco, A. - Dienstbier, M. - Salter, H. K. - Gatto, G. - Bullock, S. L.
Journal: Curr Biol

The expression of the RNA-binding factor Fragile X mental retardation protein (FMRP) is disrupted in the most common inherited form of cognitive deficiency in humans. FMRP controls neuronal morphogenesis by mediating the translational regulation and localization of a large number of mRNA targets, and these functions are closely associated with transport of FMRP complexes within neurites by microtubule-based motors. However, the mechanisms that link FMRP to motors and regulate its transport are poorly understood. Here we show that FMRP is complexed with Bicaudal-D (BicD) through a domain in the latter protein that mediates linkage of cargoes with the minus-end-directed motor dynein. We demonstrate in Drosophila that the motility and, surprisingly, levels of FMRP protein are dramatically reduced in BicD mutant neurons, leading to a paucity of FMRP within processes. We also provide functional evidence that BicD and FMRP cooperate to control dendritic morphogenesis in the larval nervous system. Our findings open new perspectives for understanding localized mRNA functions in neurons.

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Biological bifocal lenses with image separation.

Publication Date: 2010 Aug 24 PMID: 20691594
Authors: Stowasser, A. - Rapaport, A. - Layne, J. E. - Morgan, R. C. - Buschbeck, E. K.
Journal: Curr Biol

Almost all animal eyes follow a few, relatively well-understood functional plans. Only rarely do researchers discover an eye that diverges fundamentally from known types. The principal eye E2 of sunburst diving beetle (Thermonectus marmoratus) larvae clearly falls into the rarer category. On the basis of two different tests, we here report that it has truly bifocal lenses, something that has been previously suggested only for certain trilobites. Our evidence comes from (1) the relative contrast in images of a square wave grating and (2) the refraction of a narrow laser beam projected through the lens. T. marmoratus larvae have two retinas at different depths behind the lens, and these are situated so that each can receive its own focused image. This is consistent with a novel eye organization that possibly comprises "two eyes in one." Moreover, we find that in contrast to most commercial bifocal lenses, the lens of E2 exhibits asymmetry, which results in separation of the images both dorsoventrally and rostrocaudally within the layered retina. Visual contrast might thus be improved over conventional bifocal lenses because the unfocused version of one image is shifted away from the focused version of the other, an organization which could potentially be exploited in optical engineering.

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The Role of the Magnetite-Based Receptors in the Beak in Pigeon Homing.

Publication Date: 2010 Aug 4 PMID: 20691593
Authors: Wiltschko, R. - Schiffner, I. - Fuhrmann, P. - Wiltschko, W.
Journal: Curr Biol

Magnetite-containing structures in the upper beak of birds have been described as putative magnetoreceptors [1-4], but so far, all positive evidence indicating their influence on behavior has come from laboratory studies using rather unnatural stimuli (e.g., [5-7]). Here, we demonstrate these receptors' possible role in a natural situation: we released pigeons with these receptors deactivated by a local anesthetic within and outside a magnetic anomaly, together with untreated control birds. Within the anomaly, the untreated birds showed unusually long vanishing intervals and scattered bearings, indicating confusion by the anomalous magnetic conditions. Anesthesia of the beak suppressed this adverse effect. Outside the anomaly, in contrast, the treatment had little effect. These findings indicate that the receptors in the beak mediate magnetic "map" information and that this information is normally included in the navigational process yet can be replaced by nonmagnetic factors at most sites.

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Sequential Activation of Apical and Basolateral Contractility Drives Ascidian Endoderm Invagination.

Publication Date: 2010 Aug 4 PMID: 20691592
Authors: Sherrard, K. - Robin, F. - Lemaire, P. - Munro, E.
Journal: Curr Biol

BACKGROUND: Epithelial invagination is a fundamental morphogenetic behavior that transforms a flat cell sheet into a pit or groove. Previous studies of invagination have focused on the role of actomyosin-dependent apical contraction; other mechanisms remain largely unexplored. RESULTS: We combined experimental and computational approaches to identify a two-step mechanism for endoderm invagination during ascidian gastrulation. During Step 1, which immediately precedes invagination, endoderm cells constrict their apices because of Rho/Rho-kinase-dependent apical enrichment of 1P-myosin. Our data suggest that endoderm invagination itself occurs during Step 2, without further apical shrinkage, via a novel mechanism we call collared rounding: Rho/Rho-kinase-independent basolateral enrichment of 1P-myosin drives apico-basal shortening, whereas Rho/Rho-kinase-dependent enrichment of 1P and 2P myosin in circumapical collars is required to prevent apical expansion and for deep invagination. Simulations show that boundary-specific tension values consistent with these distributions of active myosin can explain the cell shape changes observed during invagination both in normal embryos and in embryos treated with pharmacological inhibitors of either Rho-kinase or Myosin II ATPase. Indeed, we find that the balance of strong circumapical and basolateral tension is the only mechanism based on differential cortical tension that can explain ascidian endoderm invagination. Finally, simulations suggest that mesectoderm cells resist endoderm shape changes during both steps, and we confirm this prediction experimentally. CONCLUSIONS: Our findings suggest that early ascidian gastrulation is driven by the coordinated apposition of circumapical and lateral endoderm contraction, working against a resisting mesectoderm. We propose that similar mechanisms may operate during other invaginations.

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Experience-driven plasticity in binocular vision.

Publication Date: 2010 Aug 24 PMID: 20674360
Authors: Klink, P. C. - Brascamp, J. W. - Blake, R. - van Wezel, R. J.
Journal: Curr Biol

Experience-driven neuronal plasticity allows the brain to adapt its functional connectivity to recent sensory input. Here we use binocular rivalry, an experimental paradigm in which conflicting images are presented to the individual eyes, to demonstrate plasticity in the neuronal mechanisms that convert visual information from two separated retinas into single perceptual experiences. Perception during binocular rivalry tended to initially consist of alternations between exclusive representations of monocularly defined images, but upon prolonged exposure, mixture percepts became more prevalent. The completeness of suppression, reflected in the incidence of mixture percepts, plausibly reflects the strength of inhibition that likely plays a role in binocular rivalry. Recovery of exclusivity was possible but required highly specific binocular stimulation. Documenting the prerequisites for these observed changes in perceptual exclusivity, our experiments suggest experience-driven plasticity at interocular inhibitory synapses, driven by the correlated activity (and also the lack thereof) of neurons representing the conflicting stimuli. This form of plasticity is consistent with a previously proposed but largely untested anti-Hebbian learning mechanism for inhibitory synapses in vision. Our results implicate experience-driven plasticity as one governing principle in the neuronal organization of binocular vision.

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Seeing mutations in living cells.

Publication Date: 2010 Aug 24 PMID: 20674359
Authors: Elez, M. - Murray, A. W. - Bi, L. J. - Zhang, X. E. - Matic, I. - Radman, M.
Journal: Curr Biol

BACKGROUND: Evolution depends on mutations: rare errors in the transmission of genetic information. Experimentally, mutations have been found by detecting altered phenotypes or sequencing complete genomes, but most mutations do not have overt phenotypes, and sequencing is expensive and has limited time resolution. The major source of mutations is DNA replication errors. Nearly all mistakes in DNA replication are detected and repaired by the mismatch repair machinery. RESULTS: We use a functional, fluorescently labeled derivative of one of the key mismatch repair proteins (MutL) to see and count the small fraction of errors in Escherichia coli that does not get repaired and is converted into stable mutations by the next round of DNA replication. Over a 300-fold range, there is a linear relationship between the frequency of fluorescent foci and the genetically measured mutation frequency, and the mean frequency of fluorescent foci agrees well with estimates of the global mutation rate. CONCLUSION: We describe a method for detecting the majority of genomic mutations emerging in living cells, independently of their potential phenotype. The distribution of emerging mutations per cell is roughly Poisson distributed, suggesting that all the cells in the population have roughly the same mutation rate.

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Feedback regulation of Ras signaling by Rabex-5-mediated ubiquitination.

Publication Date: 2010 Aug 10 PMID: 20655225
Authors: Xu, L. - Lubkov, V. - Taylor, L. J. - Bar-Sagi, D.
Journal: Curr Biol

Ras proteins play a central role in transducing signals that control cell proliferation, differentiation, motility, and survival. The location-specific signaling activity of Ras has been previously shown to be regulated by ubiquitination [1]. However, the molecular machinery that controls Ras ubiquitination has not been defined. Here we demonstrate through biochemical and functional analyses that Rabex-5 (also known as RabGEF1) [2, 3] functions as an E3 ligase for Ras. Rabex-5-mediated Ras ubiquitination promotes Ras endosomal localization and leads to the suppression of ERK activation. Moreover, the Ras effector RIN1 [4, 5] is required for Rabex-5-dependent Ras ubiquitination, suggesting a feedback mechanism by which Ras activation can be coupled to ubiquitination. These findings define new elements in the regulatory circuitry that link Ras compartmentalization to signaling output.

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Rabex-5 ubiquitin ligase activity restricts Ras signaling to establish pathway homeostasis in Drosophila.

Publication Date: 2010 Aug 10 PMID: 20655224
Authors: Yan, H. - Jahanshahi, M. - Horvath, E. A. - Liu, H. Y. - Pfleger, C. M.
Journal: Curr Biol

The Ras signaling pathway allows cells to translate external cues into diverse biological responses. Depending on context and the threshold reached, Ras signaling can promote growth, proliferation, differentiation, or cell survival. Failure to maintain precise control of Ras can have adverse physiological consequences. Indeed, excess Ras signaling disrupts developmental patterning and causes developmental disorders [1, 2], and in mature tissues, it can lead to cancer [3-5]. We identify Rabex-5 as a new component of Ras signaling crucial for achieving proper pathway outputs in multiple contexts in vivo. We show that Drosophila Rabex-5 restricts Ras signaling to establish organism size, wing vein pattern, and eye versus antennal fate. Rabex-5 has both Rab5 guanine nucleotide exchange factor (GEF) activity that regulates endocytic trafficking [6] and ubiquitin ligase activity [7, 8]. Surprisingly, overexpression studies demonstrate that Rabex-5 ubiquitin ligase activity, not its Rab5 GEF activity, is required to restrict wing vein specification and to suppress the eye phenotypes of oncogenic Ras expression. Furthermore, genetic interaction experiments indicate that Rabex-5 acts at the step of Ras, and tissue culture studies show that Rabex-5 promotes Ras ubiquitination. Together, these findings reveal a new mechanism for attenuating Ras signaling in vivo and suggest an important role for Rabex-5-mediated Ras ubiquitination in pathway homeostasis.

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Visceral-locomotory pistoning in crawling caterpillars.

Publication Date: 2010 Aug 24 PMID: 20655223
Authors: Simon, M. A. - Woods, W. A. Jr - Serebrenik, Y. V. - Simon, S. M. - van Griethuijsen, L. I. - Socha, J. J. - Lee, W. K. - Trimmer, B. A.
Journal: Curr Biol

Animals with an open coelom do not fully constrain internal tissues, and changes in tissue or organ position during body movements cannot be readily discerned from outside of the body. This complicates modeling of soft-bodied locomotion, because it obscures potentially important changes in the center of mass as a result of internal tissue movements. We used phase-contrast synchrotron X-ray imaging and transmission light microscopy to directly visualize internal soft-tissue movements in freely crawling caterpillars. Here we report a novel visceral-locomotory piston in crawling Manduca sexta larvae, in which the gut slides forward in advance of surrounding tissues. The initiation of gut sliding is synchronous with the start of the terminal prolegs' swing phase, suggesting that the animal's center of mass advances forward during the midabdominal prolegs' stance phase and is therefore decoupled from visible translations of the body. Based on synchrotron X-ray data and transmission light microscopy results, we present evidence for a two-body mechanical system with a nonlinear elastic gut that changes size and translates between the anterior and posterior of the animal. The proposed two-body system--the container and the contained--is unlike any form of legged locomotion previously reported and represents a new feature in our emerging understanding of crawling.

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Walking modulates speed sensitivity in Drosophila motion vision.

Publication Date: 2010 Aug 24 PMID: 20655222
Authors: Chiappe, M. E. - Seelig, J. D. - Reiser, M. B. - Jayaraman, V.
Journal: Curr Biol

Changes in behavioral state modify neural activity in many systems. In some vertebrates such modulation has been observed and interpreted in the context of attention and sensorimotor coordinate transformations. Here we report state-dependent activity modulations during walking in a visual-motor pathway of Drosophila. We used two-photon imaging to monitor intracellular calcium activity in motion-sensitive lobula plate tangential cells (LPTCs) in head-fixed Drosophila walking on an air-supported ball. Cells of the horizontal system (HS)--a subgroup of LPTCs--showed stronger calcium transients in response to visual motion when flies were walking rather than resting. The amplified responses were also correlated with walking speed. Moreover, HS neurons showed a relatively higher gain in response strength at higher temporal frequencies, and their optimum temporal frequency was shifted toward higher motion speeds. Walking-dependent modulation of HS neurons in the Drosophila visual system may constitute a mechanism to facilitate processing of higher image speeds in behavioral contexts where these speeds of visual motion are relevant for course stabilization.

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DNA methylation is dispensable for the growth and survival of the extraembryonic lineages.

Publication Date: 2010 Aug 24 PMID: 20637626
Authors: Sakaue, M. - Ohta, H. - Kumaki, Y. - Oda, M. - Sakaide, Y. - Matsuoka, C. - Yamagiwa, A. - Niwa, H. - Wakayama, T. - Okano, M.
Journal: Curr Biol

DNA methylation regulates development and many epigenetic processes in mammals, and it is required for somatic cell growth and survival. In contrast, embryonic stem (ES) cells can self-renew without DNA methylation. It remains unclear whether any lineage-committed cells can survive without DNA-methylation machineries. Unlike in somatic cells, DNA methylation is dispensable for imprinting and X-inactivation in the extraembryonic lineages. In ES cells, DNA methylation prevents differentiation into the trophectodermal fate. Here, we created triple-knockout (TKO) mouse embryos deficient for the active DNA methyltransferases Dnmt1, Dnmt3a, and Dnmt3b (TKO) by nuclear transfer (NT), and we examined their development. In chimeric TKO-NT and WT embryos, few TKO cells were found in the embryo proper, but they contributed to extraembryonic tissues. TKO ES cells showed increasing cell death during their differentiation into epiblast lineages, but not during differentiation into extraembryonic lineages. Furthermore, we successfully established trophoblastic stem cells (ntTS cells) from TKO-NT blastocysts. These TKO ntTS cells could self-renew, and they retained the fundamental gene expression patterns of stem cells. Our findings indicated that extraembryonic-lineage cells can survive and proliferate in the absence of DNA methyltransferases and that a cell's response to the stress of epigenomic damage is cell type dependent.

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Specific dopaminergic neurons for the formation of labile aversive memory.

Publication Date: 2010 Aug 24 PMID: 20637624
Authors: Aso, Y. - Siwanowicz, I. - Bracker, L. - Ito, K. - Kitamoto, T. - Tanimoto, H.
Journal: Curr Biol

A paired presentation of an odor and electric shock induces aversive odor memory in Drosophila melanogaster. Electric shock reinforcement is mediated by dopaminergic neurons, and it converges with the odor signal in the mushroom body (MB). Dopamine is synthesized in approximately 280 neurons that form distinct cell clusters and is involved in a variety of brain functions. Recently, one of the dopaminergic clusters (PPL1) that includes MB-projecting neurons was shown to signal reinforcement for aversive odor memory. As each dopaminergic cluster contains multiple types of neurons with different projections and physiological characteristics, functional understanding of the circuit for aversive memory requires cellular identification. Here, we show that MB-M3, a specific type of dopaminergic neurons in the PAM cluster, is preferentially required for the formation of labile memory. Strikingly, flies formed significant aversive odor memory without electric shock when MB-M3 was selectively stimulated together with odor presentation. In addition, we identified another type of dopaminergic neurons in the PPL1 cluster, MB-MP1, which can induce aversive odor memory. As MB-M3 and MB-MP1 target the distinct subdomains of the MB, these reinforcement circuits might induce different forms of aversive memory in spatially segregated synapses in the MB.

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The hippocampus plays a selective role in the retrieval of detailed contextual memories.

Publication Date: 2010 Aug 10 PMID: 20637623
Authors: Wiltgen, B. J. - Zhou, M. - Cai, Y. - Balaji, J. - Karlsson, M. G. - Parivash, S. N. - Li, W. - Silva, A. J.
Journal: Curr Biol

BACKGROUND: It is widely believed that the hippocampus plays a temporary role in the retrieval of episodic and contextual memories. Initial research indicated that damage to this structure produced amnesia for newly acquired memories but did not affect those formed in the distant past. A number of recent studies, however, have found that the hippocampus is required for the retrieval of episodic and contextual memories regardless of their age. These findings are currently the subject of intense debate, and a satisfying resolution has yet to be identified. RESULTS: The current experiments address this issue by demonstrating that detailed memories require the hippocampus, whereas memories that lose precision become independent of this structure. First, we show that the dorsal hippocampus is preferentially activated by the retrieval of detailed contextual fear memories. We then establish that the hippocampus is necessary for the retrieval of detailed memories by using a context-generalization procedure. Mice that exhibit high levels of generalization to a novel environment show no memory loss when the hippocampus is subsequently inactivated. In contrast, mice that discriminate between contexts are significantly impaired by hippocampus inactivation. CONCLUSIONS: Our data suggest that detailed contextual memories require the hippocampus, whereas memories that lose precision can be retrieved without this structure. These findings can account for discrepancies in the literature-memories of our distant past can be either lost or retained after hippocampus damage depending on their quality-and provide a new framework for understanding memory consolidation.

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Determinants of divergent adaptation and dobzhansky-muller interaction in experimental yeast populations.

Publication Date: 2010 Aug 10 PMID: 20637622
Authors: Anderson, J. B. - Funt, J. - Thompson, D. A. - Prabhu, S. - Socha, A. - Sirjusingh, C. - Dettman, J. R. - Parreiras, L. - Guttman, D. S. - Regev, A. - Kohn, L. M.
Journal: Curr Biol

Divergent adaptation can be associated with reproductive isolation in speciation [1]. We recently demonstrated the link between divergent adaptation and the onset of reproductive isolation in experimental populations of the yeast Saccharomyces cerevisiae evolved from a single progenitor in either a high-salt or a low-glucose environment [2]. Here, whole-genome resequencing and comparative genome hybridization of representatives of three populations revealed 17 mutations, six of which explained the adaptive increases in mitotic fitness. In two populations evolved in high salt, two different mutations occurred in the proton efflux pump gene PMA1 and the global transcriptional repressor gene CYC8; the ENA genes encoding sodium efflux pumps were overexpressed once through expansion of this gene cluster and once because of mutation in the regulator CYC8. In the population from low glucose, one mutation occurred in MDS3, which modulates growth at high pH, and one in MKT1, a global regulator of mRNAs encoding mitochondrial proteins, the latter recapitulating a naturally occurring variant. A Dobzhansky-Muller (DM) incompatibility between the evolved alleles of PMA1 and MKT1 strongly depressed fitness in the low-glucose environment. This DM interaction is the first reported between experimentally evolved alleles of known genes and shows how reproductive isolation can arise rapidly when divergent selection is strong.

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An olfactory subsystem that detects carbon disulfide and mediates food-related social learning.

Publication Date: 2010 Aug 24 PMID: 20637621
Authors: Munger, S. D. - Leinders-Zufall, T. - McDougall, L. M. - Cockerham, R. E. - Schmid, A. - Wandernoth, P. - Wennemuth, G. - Biel, M. - Zufall, F. - Kelliher, K. R.
Journal: Curr Biol

Olfactory signals influence social interactions in a variety of species. In mammals, pheromones and other social cues can promote mating or aggression behaviors; can communicate information about social hierarchies, genetic identity and health status; and can contribute to associative learning. However, the molecular, cellular, and neural mechanisms underlying many olfactory-mediated social interactions remain poorly understood. Here, we report that a specialized olfactory subsystem that includes olfactory sensory neurons (OSNs) expressing the receptor guanylyl cyclase GC-D, the cyclic nucleotide-gated channel subunit CNGA3, and the carbonic anhydrase isoform CAII (GC-D(+) OSNs) is required for the acquisition of socially transmitted food preferences (STFPs) in mice. Using electrophysiological recordings from gene-targeted mice, we show that GC-D(+) OSNs are highly sensitive to the volatile semiochemical carbon disulfide (CS(2)), a component of rodent breath and a known social signal mediating the acquisition of STFPs. Olfactory responses to CS(2) are drastically reduced in mice lacking GC-D, CNGA3, or CAII. Disruption of this sensory transduction cascade also results in a failure to acquire STFPs from either live or surrogate demonstrator mice or to exhibit hippocampal correlates of STFP retrieval. Our findings indicate that GC-D(+) OSNs detect chemosignals that facilitate food-related social interactions.

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Path integration provides a scaffold for landmark learning in desert ants.

Publication Date: 2010 Aug 10 PMID: 20619653
Authors: Muller, M. - Wehner, R.
Journal: Curr Biol

On leaving the nest [1-9] or a newly discovered food site [10-12] for the first time, bees and wasps perform elaborate flight maneuvers to learn the location of their goal and the lay of the land surrounding it. In all these orientation flights the insects turn back and look [13] at the goal, which they can visually locate by landmark cues directly defining the goal. Here we show that Namibian desert ants, Ocymyrmex, when learning new landmarks in the neighborhood of the goal, acquire this landmark information when they cannot see the goal. They do so by performing well-choreographed rotation movements integrated in spiral-like "learning walks." Within these rotations, short (about 150 ms) stopping phases occur, during which the ants orient themselves in the direction of the nest entrance. On the barren sand surface the nest entrance is invisible, so the ants can aim at it only by reading out the current state of their path integrator [14-17]. Hence, they could associate "snapshot" views [18-20] taken of the nest surroundings during the stopping phases with path integration coordinates. In bees and ants such associations have often been discussed, but evidence has not been obtained yet [15, 20-22].

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Shedding of the mucin-like flocculin Flo11p reveals a new aspect of fungal adhesion regulation.

Publication Date: 2010 Aug 10 PMID: 20619652
Authors: Karunanithi, S. - Vadaie, N. - Chavel, C. A. - Birkaya, B. - Joshi, J. - Grell, L. - Cullen, P. J.
Journal: Curr Biol

Cell adhesion is a key feature in the regulation of many biological processes. In the budding yeast Saccharomyces cerevisiae, Flo11p is the major adhesion molecule that controls filamentous growth [1-3] and the expansion of interconnected cells in mats or biofilms [4]. We show here that Flo11p is shed from cells. Flo11p shedding attenuated adherence and contributed to the overall balance in adherence properties that was optimal for filamentous growth and mat formation. Shed Flo11p comprised an essential component of a fluid layer surrounding yeast mats that may be functionally analogous to the mucus secretions of higher eukaryotes. Genome-wide secretion profiling of Flo11p identified new regulatory proteins, including the furin protease Kex2p, which was required for cleavage and maturation of the Flo11p protein. Secreted mucin-like proteins may play unexpected roles in the adherence properties and virulence of microbial pathogens.

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Relocation of the chromosomal passenger complex prevents mitotic checkpoint engagement at anaphase.

Publication Date: 2010 Aug 10 PMID: 20619651
Authors: Vazquez-Novelle, M. D. - Petronczki, M.
Journal: Curr Biol

The mitotic checkpoint monitors the attachment of kinetochores to microtubules and delays anaphase onset until all sister kinetochores have become attached to opposite poles [1, 2]. Correct bipolar attachment leads to kinetochore deformation and tension and satisfies the checkpoint [3-6]. What prevents mitotic checkpoint reactivation when sister centromeres are split and tension is lost at anaphase onset? Aurora B kinase, the catalytic subunit of the chromosomal passenger protein complex (CPC) [7], acts as a sensor at inner centromeres for the status of attachment [5, 8]. Phosphorylation of Aurora B targets at erroneously attached kinetochores elicits the correction of these attachments and the activation of the mitotic checkpoint. At anaphase, the CPC leaves the centromeres and relocates to the spindle midzone [7]. This iconic translocation might prevent the checkpoint from reengaging after anaphase onset. To test this hypothesis, we experimentally retained Aurora B and the CPC at the centromere throughout anaphase in human cells. Preventing CPC translocation caused the untimely recruitment of mitotic checkpoint proteins to kinetochores at anaphase in an Aurora B kinase activity-dependent manner. Our results suggest that the relocalization of the CPC, an evolutionarily conserved event in eukaryotes, is a key mechanism that incapacitates the mitotic checkpoint at anaphase.

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Sli15(INCENP) dephosphorylation prevents mitotic checkpoint reengagement due to loss of tension at anaphase onset.

Publication Date: 2010 Aug 10 PMID: 20619650
Authors: Mirchenko, L. - Uhlmann, F.
Journal: Curr Biol

The mitotic checkpoint, also known as the spindle assembly checkpoint, delays anaphase onset until all chromosomes have reached bipolar tension on the mitotic spindle [1-3]. Once this is achieved, the protease separase is activated to cleave the chromosomal cohesin complex, thereby triggering anaphase. Cohesin cleavage releases tension between sister chromatids, but why the mitotic checkpoint now remains silent is poorly understood. Here, using budding yeast as a model, we show that loss of sister chromatid cohesion at anaphase onset would engage the mitotic checkpoint if this was not prevented by concomitant separase-dependent activation of the Cdc14 phosphatase. Cdc14, in turn, inactivates the mitotic checkpoint by dephosphorylating Sli15(INCENP), a subunit of the conserved Aurora B kinase complex that forms part of the proposed chromosomal tension sensor. Dephosphorylation-dependent relocation of Sli15(INCENP) from centromeres to the central spindle during anaphase is seen in organisms from yeast to human [4-8]. Our results suggest that Sli15(INCENP) dephosphorylation is part of an evolutionarily conserved mechanism that prevents the mitotic checkpoint from reengaging when tension between sister chromatids is lost at anaphase onset.

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Others' actions reduce crossmodal integration in peripersonal space.

Publication Date: 2010 Aug 10 PMID: 20619649
Authors: Heed, T. - Habets, B. - Sebanz, N. - Knoblich, G.
Journal: Curr Biol

Specific mechanisms integrate visual-tactile information close to the body to guide voluntary action [1, 2] and to enable rapid self-defense in peripersonal space [3-5]. In social interactions, others frequently act in one's peripersonal space, thereby changing the relevance of near-body events for one's own actions. Such changes of stimulus relevance may thus affect visual-tactile integration. Here we show that crossmodal processing in peripersonal space is reduced for perceptual events that another person acts upon. Participants performed a visual-tactile interference task [6] in which spatially incongruent visual distractors in the peripersonal space are known to interfere with judging the location of a tactile stimulus [7-10]. Participants performed the task both alone and with a partner who responded to the visual distractors. Performing the task together reduced the crossmodal interference effect on tactile judgments, but only if the partner occupied the participant's peripersonal space (experiment 1) and if she responded to all, rather than only a subset, of the visual distractors (experiment 2). These results show that others' actions can modulate multisensory integration in peripersonal space in a top-down fashion. Such modulations may serve to guide voluntary action and to allow others' actions in a space of self-defense.

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ASPP2 regulates epithelial cell polarity through the PAR complex.

Publication Date: 2010 Aug 10 PMID: 20619648
Authors: Cong, W. - Hirose, T. - Harita, Y. - Yamashita, A. - Mizuno, K. - Hirano, H. - Ohno, S.
Journal: Curr Biol

The PAR complex, consisting of the evolutionarily conserved PAR-3, PAR-6, and aPKC, regulates cell polarity in many cell types, including epithelial cells [1-4]. Consistently, genetic manipulation of its components affects tissue integrity in multiple biological systems [5-9]. However, the regulatory mechanisms of the PAR complex remain obscure. We report here that apoptosis-stimulating protein of p53 (ASPP2 or TP53BP2), which binds to the tumor suppressor p53 and stimulates its proapoptotic function [10-12], positively regulates epithelial cell polarity by associating with the PAR complex. ASPP2 interacts and colocalizes with PAR-3 at apical cell-cell junctions in the polarized epithelial cells. Depletion of ASPP2 in epithelial cells causes defects in cell polarity, such as the formation of tight junctions and the maintenance and development of apical membrane domains. Moreover, depletion of ASPP2 causes a defect in PAR-3 localization, as well as vice versa. Furthermore, disturbance in the interaction between ASPP2 and PAR-3 causes defects in cell polarity. We conclude that ASPP2 regulates epithelial cell polarity in cooperation with PAR-3 to form an active PAR complex. Our results, taken together with the known functions of ASPP2, suggest a close relationship between cell polarity and other cell regulatory mechanisms mediated by ASPP2.

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Fitness-associated sexual reproduction in a filamentous fungus.

Publication Date: 2010 Aug 10 PMID: 20598542
Authors: Schoustra, S. - Rundle, H. D. - Dali, R. - Kassen, R.
Journal: Curr Biol

Sex is a long-standing evolutionary enigma. Although the majority of eukaryotes reproduce sexually at least sometimes [1-3], the evolution of sex from an asexual ancestor has been difficult to explain because it requires sexually reproducing lineages to overcome the manifold costs of sex, including the destruction of favorable gene combinations created by selection [4, 5]. Conditions for the evolution of sex are much broader if individuals can reproduce either sexually or asexually (i.e., facultative sex) and allocate disproportionately more resources to sex when their fitness is low (fitness-associated-sex or FAS [6-10]). Although facultatively sexual organisms have been shown to engage in more sex when stressed [11], direct evidence for FAS is lacking. We provide evidence using 53 genotypes of the filamentous fungus Aspergillus nidulans in a reciprocal transplant experiment across three environments. Different genotypes achieved highest fitness in different environments and genotypes invested relatively more in sex in environments in which their fitness was lower, showing that allocation to sexual reproduction is a function of how well-adapted a genotype is to its environment. FAS in A. nidulans is unlikely to have evolved as a strategy to resist or avoid stress because asexual spores are more dispersive and equally resistant [12, 13].

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Strong and consistent social bonds enhance the longevity of female baboons.

Publication Date: 2010 Aug 10 PMID: 20598541
Authors: Silk, J. B. - Beehner, J. C. - Bergman, T. J. - Crockford, C. - Engh, A. L. - Moscovice, L. R. - Wittig, R. M. - Seyfarth, R. M. - Cheney, D. L.
Journal: Curr Biol

Longevity is a major component of variation in fitness in long-lived iteroparous species [1-4]. Among female baboons, variation in breeding lifespan accounts for approximately 50% of the variation in lifetime fitness [5, 6]. However, we know little about the causes of variation in longevity in primates or other long-lived mammals. Savannah baboons form strong, equitable, and enduring relationships with specific female partners, particularly with close relatives and agemates [7-10]. The quality of females' social relationships influences their ability to cope with stressful events [11-13] and is associated with variation in female reproductive success [9, 14]. Here we show that dominance rank and the quality of close social bonds have independent effects on the longevity of female chacma baboons (Papio hamadryas ursinus). High-ranking females live longer than lower-ranking females. In addition, females who form stronger and more stable social bonds with other females live significantly longer than females who form weaker and less stable relationships. These data extend our understanding of the adaptive value of social bonds in baboons and complement a growing body of evidence that indicates that social bonds have adaptive value in a range of taxa, from mice to humans [9, 14-19].

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Olfaction modulates visual perception in binocular rivalry.

Publication Date: 2010 Aug 10 PMID: 20598540
Authors: Zhou, W. - Jiang, Y. - He, S. - Chen, D.
Journal: Curr Biol

Vision is widely accepted as the dominant sense in larger primates including humans, whereas olfaction is often considered a vestigial sense yielding only obscure object representations [1]. It is well documented that vision drives olfactory perception [2, 3], but there has been little indication that olfaction could modulate visual perception. Here we introduce smells to a well-established visual phenomenon termed binocular rivalry, perceptual alternations that occur when distinctively different images are separately presented to the two eyes [4]. We show that an odorant congruent to one of the competing images prolongs the time that image is visible and shortens its suppression time in a manner that is automatic, essentially independent of cognitive control, and partly subconscious. Our findings provide the first direct evidence that an olfactory cue biases the dynamic process of binocular rivalry, thereby demonstrating olfactory modulation of visual perception-an effect that has been hitherto unsuspected.

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Visual sensitivity underlying changes in visual consciousness.

Publication Date: 2010 Aug 10 PMID: 20598538
Authors: Alais, D. - Cass, J. - O'Shea, R. P. - Blake, R.
Journal: Curr Biol

When viewing a different stimulus with each eye, we experience the remarkable phenomenon of binocular rivalry: alternations in consciousness between the stimuli [1, 2]. According to a popular theory first proposed in 1901, neurons encoding the two stimuli engage in reciprocal inhibition [3-8] so that those processing one stimulus inhibit those processing the other, yielding consciousness of one dominant stimulus at any moment and suppressing the other. Also according to the theory, neurons encoding the dominant stimulus adapt, weakening their activity and the inhibition they can exert, whereas neurons encoding the suppressed stimulus recover from adaptation until the balance of activity reverses, triggering an alternation in consciousness. Despite its popularity, this theory has one glaring inconsistency with data: during an episode of suppression, visual sensitivity to brief probe stimuli in the dominant eye should decrease over time and should increase in the suppressed eye, yet sensitivity appears to be constant [9, 10]. Using more appropriate probe stimuli (experiment 1) in conjunction with a new method (experiment 2), we found that sensitivities in dominance and suppression do show the predicted complementary changes.

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Synergistic activation of phospholipase C-beta3 by Galpha(q) and Gbetagamma describes a simple two-state coincidence detector.

Publication Date: 2010 Aug 10 PMID: 20579885
Authors: Philip, F. - Kadamur, G. - Silos, R. G. - Woodson, J. - Ross, E. M.
Journal: Curr Biol

BACKGROUND: Receptors that couple to G(i) and G(q) often interact synergistically in cells to elicit cytosolic Ca(2+) transients that are several-fold higher than the sum of those driven by each receptor alone. Such synergism is commonly assumed to be complex, requiring regulatory interaction between components, multiple pathways, or multiple states of the target protein. RESULTS: We show that cellular G(i)-G(q) synergism derives from direct supra-additive stimulation of phospholipase C-beta3 (PLC-beta3) by G protein subunits Gbetagamma and Galpha(q), the relevant components of the G(i) and G(q) signaling pathways. No additional pathway or proteins are required. Synergism is quantitatively explained by the classical and simple two-state (inactive<-->active) allosteric mechanism. We show generally that synergistic activation of a two-state enzyme reflects enhanced conversion to the active state when both ligands are bound, not merely the enhancement of ligand affinity predicted by positive cooperativity. The two-state mechanism also explains why synergism is unique to PLC-beta3 among the four PLC-beta isoforms and, in general, why one enzyme may respond synergistically to two activators while another does not. Expression of synergism demands that an enzyme display low basal activity in the absence of ligand and becomes significant only when basal activity is
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