Monday, May 9, 2011

Hot off the presses! May 10 Curr Bio

The May 10 issue of the Curr Bio is now up on Pubget (About Curr Bio): 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:

  • Myrmecomorphomania
    - Curr Bio 21(9):R291-R293 (2011)
    Ants are so abundant that mimicking them has become a profitable way of life for many species. Florian Maderspacher and Marcus Stensmyr take a trip into the world of ant mimicry.
  • Genomics in permanent revolution
    - Curr Bio 21(9):R294-R297 (2011)
    Only six years after 'next generation' sequencing sent the cost of a human genome spiralling downwards, a third generation now promises single molecule read-out and electronic detection. Michael Gross reports.
  • Neutrophil extracellular traps
    - Curr Bio 21(9):R297-R298 (2011)
  • Iva Tolic-Nørrelykke
    - Curr Bio 21(9):R299-R300 (2011)
  • Appetitive Learning: Memories Need Calories
    - Curr Bio 21(9):R301-R302 (2011)
    Recent studies of the way animals learn challenge the idea that food learning relies mainly on how food tastes. Work on Drosophila has now shown that flies must ingest food with a metabolic benefit to form a lasting memory for a learned odour.
  • Cell Migration: Katanin Gives Microtubules a Trim
    - Curr Bio 21(9):R302-R304 (2011)
    New evidence suggests that katanin — best known for severing microtubules in their more stable regions — localizes at the leading edge of migratory cells and trims microtubules at their dynamic plus ends.
  • Circadian Rhythms: Biological Clocks Work in Phospho-Time
    - Curr Bio 21(9):R305-R307 (2011)
    The 24 hour molecular oscillator requires precisely calibrated degradation of core clock proteins, like PERIOD. New studies shed light on a sequential series of PERIOD phosphorylation events that first inhibits, then accelerates PERIOD degradation.
  • Pollinator Attraction: The Importance of Looking Good and Smelling Nice
    - Curr Bio 21(9):R307-R309 (2011)
    Flowers entice animal pollinators using a complex array of attractions. Reciprocal transfer of traits between Petunia species now shows that colour and scent are equally important to hawkmoths in choosing between different flowers.
  • Mechanotransduction: Getting Morphogenesis Down Pat
    - Curr Bio 21(9):R309-R311 (2011)
    Embryonic morphogenesis requires the coordination of forces across multiple tissues and their associated extracellular matrices. A new study reports a mechanical feedback loop in the Caenorhabditis elegans embryo between muscle and epidermis that may provide a model for understanding how tissues coordinate morphogenetic events in the embryo.
  • Animal Cognition: Monkeys Recall Previously Seen Images
    - Curr Bio 21(9):R311-R313 (2011)
    A recent study has found that rhesus macaques can recall newly presented shapes: this demonstration of recall in non-human primates suggests that some animals have recollection processes similar to those of humans.
  • Circadian Biology: The Supporting Cast Takes On a Starring Role
    - Curr Bio 21(9):R313-R314 (2011)
    Brain circuits are generally thought to consist solely of neurons communicating with other neurons. In Drosophila, glia-to-neuron signaling has now been shown to be critical to the function of the circadian circuit.
  • Malaria: Surprising Mechanism of Merozoite Egress Revealed
    - Curr Bio 21(9):R314-R316 (2011)
    A recent study reveals that the intraerythrocytic asexual reproduction cycle of Plasmodium falciparum ends with the ruptured erythrocyte membrane curling outwards, buckling, everting and vesiculating. Analogy with the sequence seen during spontaneous inside-out vesiculation of erythrocyte membranes suggests that the parasite co-opts pre-existing cytoskeletal conformations to facilitate terminal merozoite dispersal.
  • Plant Signalling Pathways: A Comparative Evolutionary Overview
    - Curr Bio 21(9):R317-R319 (2011)
  • Two-Component Systems and Their Co-Option for Eukaryotic Signal Transduction
    - Curr Bio 21(9):R320-R330 (2011)
    Two-component signaling pathways involve histidine kinases, response regulators, and sometimes histidine-containing phosphotransfer proteins. Prevalent in prokaryotes, these signaling elements have also been co-opted to meet the needs of signal transduction in eukaryotes such as fungi and plants. Here we consider the evolution of such regulatory systems, with a particular emphasis on the roles they play in signaling by the plant hormones cytokinin and ethylene, in phytochrome-mediated perception of light, and as integral components of the circadian clock.
  • Auxin, Self-Organisation, and the Colonial Nature of Plants
    - Curr Bio 21(9):R331-R337 (2011)
    Evolution has provided at least two particularly successful independent solutions to the problems of multicellularity — animals and higher plants. An obvious requirement for successful multicellularity is communication between different parts of the organism, both locally, for example between neighbouring cells, and over very long distances. Recent advances in understanding hormone signalling networks in plants are beginning to reveal how co-ordination of activity across the whole plant body can be achieved despite the lack of a control centre, typical of animal systems. Of particular importance in this distributed regulatory approach are the self-organising properties of the transport system for the plant hormone auxin. This review examines the integrative role of the auxin transport network in co-ordinating plant growth and development.
  • The Molecular Mechanism and Evolution of the GA–GID1–DELLA Signaling Module in Plants
    - Curr Bio 21(9):R338-R345 (2011)
    Bioactive gibberellins (GAs) are diterpene phytohormones that modulate growth and development throughout the whole life cycle of the flowering plant. Impressive advances have been made in elucidating the GA pathway with the cloning and characterization of genes encoding most GA biosynthesis and catabolism enzymes, GA receptors (GIBBERELLIN INSENSITIVE DWARF1, GID1) and early GA signaling components. Recent biochemical, genetic and structural analyses demonstrate that GA de-represses its signaling pathway by GID1-induced degradation of DELLA proteins, which are master growth repressors, via a ubiquitin–proteasome pathway. Multiple endogenous signals and environmental cues also interact with the GA–GID1–DELLA regulatory module by affecting the expression of GA metabolism genes, and hence GA content and DELLA levels. Importantly, DELLA integrates different signaling activities by direct protein–protein interaction with multiple key regulatory proteins from other p! athways. Comparative studies suggest that the functional GA–GID1–DELLA module is highly conserved among vascular plants, but not in the bryophytes. Interestingly, differentiation of the moss Physcomitrella patens is regulated by as yet unidentified ent-kaurene-derived diterpenes, which are distinct from the common active GAs in vascular plants.
  • Evolution of Abscisic Acid Synthesis and Signaling Mechanisms
    - Curr Bio 21(9):R346-R355 (2011)
    The plant hormone abscisic acid (ABA) mediates seed dormancy, controls seedling development and triggers tolerance to abiotic stresses, including drought. Core ABA signaling components consist of a recently identified group of ABA receptor proteins of the PYRABACTIN RESISTANCE (PYR)/REGULATORY COMPONENT OF ABA RECEPTOR (RCAR) family that act as negative regulators of members of the PROTEIN PHOSPHATASE 2C (PP2C) family. Inhibition of PP2C activity enables activation of SNF1-RELATED KINASE 2 (SnRK2) protein kinases, which target downstream components, including transcription factors, ion channels and NADPH oxidases. These and other components form a complex ABA signaling network. Here, an in depth analysis of the evolution of components in this ABA signaling network shows that (i) PYR/RCAR ABA receptor and ABF-type transcription factor families arose during land colonization of plants and are not found in algae and other species, (ii) ABA biosynthesis enzymes have evolve! d to plant- and fungal-specific forms, leading to different ABA synthesis pathways, (iii) existing stress signaling components, including PP2C phosphatases and SnRK kinases, were adapted for novel roles in this plant-specific network to respond to water limitation. In addition, evolutionarily conserved secondary structures in the PYR/RCAR ABA receptor family are visualized.
  • Peptide Signaling in Plant Development
    - Curr Bio 21(9):R356-R364 (2011)
    Cell-to-cell communication is integral to the evolution of multicellularity. In plant development, peptide signals relay information coordinating cell proliferation and differentiation. These peptides are often encoded by gene families and bind to corresponding families of receptors. The precise spatiotemporal expression of signals and their cognate receptors underlies developmental patterning, and expressional and biochemical changes over evolutionary time have likely contributed to the refinement and complexity of developmental programs. Here, we discuss two major plant peptide families which have central roles in plant development: the CLAVATA3/ENDOSPERM SURROUNDING REGION (CLE) peptide family and the EPIDERMAL PATTERNING FACTOR (EPF) family. We discuss how specialization has enabled the CLE peptides to modulate stem cell differentiation in various tissue types, and how differing activities of EPF peptides precisely regulate the stomatal developmental program, and w! e examine the contributions of these peptide families to plant development from an evolutionary perspective.
  • Hormone Signalling Crosstalk in Plant Growth Regulation
    - Curr Bio 21(9):R365-R373 (2011)
    The remarkable plasticity of plant ontogeny is shaped by hormone pathways, which not only orchestrate intrinsic developmental programs, but also convey environmental inputs. Several classes of plant hormones exist, and among them auxin, brassinosteroid and gibberellin are central for the regulation of growth in general and of cell elongation in particular. Various growth phenomena can be modulated by each of the three hormones, in a sometimes synergistic fashion, suggesting physiological redundancy and/or crosstalk between the different pathways. Whether this means that they target a common and unique transcriptome module, or rather separate growth-promoting transcriptome modules, remains unclear, however. Nevertheless, while surprisingly few molecular mediators of direct crosstalk in the proper sense have been isolated, evidence is accumulating for complex cross-regulatory relations between hormone pathways at the level of transcription, as exemplified in root meriste! m growth. The growing number of available genome sequences from the green lineage offers first glimpses at the evolution of hormone pathways, which can aid in understanding the multiple relationships observed between these pathways in angiosperms. The available analyses suggest that auxin, gibberellin and brassinosteroid signalling arose during land plant evolution in this order, correlating with increased morphological complexity and possibly conferring increased developmental flexibility.
  • FT, A Mobile Developmental Signal in Plants
    - Curr Bio 21(9):R374-R378 (2011)
    Plants synchronise their flowering with the seasons to maximise reproductive fitness. While plants sense environmental conditions largely through the leaves, the developmental decision to flower occurs in the shoot apex, requiring the transmission of flowering information, sometimes over quite long distances. Interestingly, despite the enormous diversity of reproductive strategies and lifestyles of higher plants, a key component of this mobile flowering signal, or florigen, is contributed by a highly conserved gene: FLOWERING LOCUS T (FT). The FT gene encodes a small globular protein that is able to translocate from the leaves to the shoot apex through the phloem. Plants have evolved a variety of regulatory networks that control FT expression in response to diverse environmental signals, enabling flowering and other developmental responses to be seasonally timed. As well as playing a key role in flowering, recent discoveries indicate FT is also involved in other develo! pmental processes in the plant, including dormancy and bud burst.
  • QUASIMODO, a Novel GPI-Anchored Zona Pellucida Protein Involved in Light Input to the Drosophila Circadian Clock
    - Curr Bio 21(9):719-729 (2011)
    Background Circadian clocks are synchronized to the solar day via visual and specialized photoreceptors. In Drosophila, CRYPTOCHROME (CRY) is a major photoreceptor that mediates resetting of the circadian clock via light-dependent degradation of the clock protein TIMELESS (TIM). However, in the absence of CRY, this TIM-mediated resetting still occurs in some pacemaker neurons, resulting in synchronized behavioral rhythms when flies are exposed to light-dark cycles. Even in the additional absence of visual photoreception, partial molecular and behavioral light synchronization persists. Therefore, other important clock-related photoreceptive and synchronization mechanisms must exist. Results We identified a novel clock-controlled gene (quasimodo) that encodes a light-responsive and membrane-anchored Zona Pellucida domain protein that supports light-dependent TIM degradation. Whereas wild-type flies become arrhythmic in constant light (LL), quasimodo mutants elicit rhythmic expression of clock proteins and behavior in LL. QUASIMODO (QSM) can function independently of CRY and is predominantly expressed within CRY-negative clock neurons. Interestingly, downregulation of qsm in the clock circuit restores LL clock protein rhythms in qsm-negative neurons, indicating that qsm-mediated light input is not entirely cell autonomous and can be accessed by the clock circuit. Conclusions Our findings indicate that QSM constitutes part of a novel and CRY-independent light input to the circadian clock. Like CRY, this pathway targets the clock protein TIM. QSM's light-responsive character in conjunction with the predicted localization at the outer neuronal membrane suggests that its function is linked to a yet unidentified membrane-bound photoreceptor.
  • Pollinator Choice in Petunia Depends on Two Major Genetic Loci for Floral Scent Production
    - Curr Bio 21(9):730-739 (2011)
    Background Differences in floral traits, such as petal color, scent, morphology, or nectar quality and quantity, can lead to specific interactions with pollinators and may thereby cause reproductive isolation. Petunia provides an attractive model system to study the role of floral characters in reproductive isolation and speciation. The night-active hawkmoth pollinator Manduca sexta relies on olfactory cues provided by Petunia axillaris. In contrast, Petunia exserta, which displays a typical hummingbird pollination syndrome, is devoid of scent. The two species can easily be crossed in the laboratory, which makes it possible to study the genetic basis of the evolution of scent production and the importance of scent for pollinator behavior. Results In an F2 population derived from an interspecific cross between P. axillaris and P. exserta, we identified two quantitative trait loci (QTL) that define the difference between the two species' ability to produce benzenoid volatiles. One of these loci was identified as the MYB transcription factor ODORANT1. Reciprocal introgressions of scent QTL were used for choice experiments under controlled conditions. These experiments demonstrated that the hawkmoth M. sexta prefers scented plants and that scent determines choice at a short distance. When exposed to conflicting cues of color versus scent, the insects display no preference, indicating that color and scent are equivalent cues. Conclusion Our results show that scent is an important flower trait that defines plant-pollinator interactions at the level of individual plants. The genetic basis underlying such a major phenotypic difference appears to be relatively simple and may enable rapid loss or gain of scent through hybridization. Video Abstract To view the video inline, enable JavaScript on your browser. However, you can download and view the video by clicking on the icon below Download this Video (15441 K)
  • Visual Motion Induces a Forward Prediction of Spatial Pattern
    - Curr Bio 21(9):740-745 (2011)
    Cortical motion analysis continuously encodes image velocity but might also be used to predict future patterns of sensory input along the motion path. We asked whether this predictive aspect of motion is exploited by the human visual system. Targets can be more easily detected at the leading as compared to the trailing edge of motion [1], but this effect has been attributed to a nonspecific boost in contrast gain at the leading edge, linked to motion-induced shifts in spatial position [[1], [2], [3] and [4]]. Here we show that the detectability of a local sinusoidal target presented at the ends of a region containing motion is phase dependent at the leading edge, but not at the trailing edge. These two observations rule out a simple gain control mechanism that modulates contrast energy and passive filtering explanations, respectively. By manipulating the relative orientation of the moving pattern and target, we demonstrate that the resulting spatial variation in detect! ion threshold along the edge closely resembles the superposition of sensory input and an internally generated predicted signal. These findings show that motion induces a forward prediction of spatial pattern that combines with the cortical representation of the future stimulus.
  • Remembering Nutrient Quality of Sugar in Drosophila
    - Curr Bio 21(9):746-750 (2011)
    Taste is an early stage in food and drink selection for most animals [[1] and [2]]. Detecting sweetness indicates the presence of sugar and possible caloric content. However, sweet taste can be an unreliable predictor of nutrient value because some sugars cannot be metabolized. In addition, discrete sugars are detected by the same sensory neurons in the mammalian [3] and insect [[4] and [5]] gustatory systems, making it difficult for animals to readily distinguish the identity of different sugars using taste alone [[6], [7] and [8]]. Here we used an appetitive memory assay in Drosophila [[9], [10] and [11]] to investigate the contribution of palatability and relative nutritional value of sugars to memory formation. We show that palatability and nutrient value both contribute to reinforcement of appetitive memory. Nonnutritious sugars formed less robust memory that could be augmented by supplementing with a tasteless but nutritious substance. Nutrient information is con! veyed to the brain within minutes of training, when it can be used to guide expression of a sugar-preference memory. Therefore, flies can rapidly learn to discriminate between sugars using a postingestive reward evaluation system, and they preferentially remember nutritious sugars.
  • Drosophila Evaluates and Learns the Nutritional Value of Sugars
    - Curr Bio 21(9):751-755 (2011)
    Living organisms need to search for and ingest nutritional chemicals, and gustation plays a major role in detecting and discriminating between chemicals present in the environment. Using Drosophila as a model organism, we asked whether animals have the ability to evaluate the nutritional value of sugars. In flies, chemosensilla on the tarsi and labellum are the gustatory organs used to discriminate between edible and nonedible compounds [[1] and [2]]. We noticed that Drosophila do not assign nutritional values to all sweet chemicals. D-arabinose is sweet to flies, but it provides them with no nutrition. By contrast, the sugar alcohol D-sorbitol is not sensed as sweet, but flies can live on it. We performed behavioral and electrophysiological measurements to confirm these gustatory and feeding responses. We found that Drosophila can learn the nutritional value of nonsweet D-sorbitol when it is associated with an odor cue. The learning process involved the synapsin molec! ule, suggesting that a neuronal mechanism is involved. We propose that Drosophila uses neural machinery to detect, evaluate, and learn the nutritional value of foods after ingestion.
  • NEMO Kinase Contributes to Core Period Determination by Slowing the Pace of the Drosophila Circadian Oscillator
    - Curr Bio 21(9):756-761 (2011)
    The Drosophila circadian oscillator is comprised of transcriptional feedback loops that are activated by CLOCK (CLK) and CYCLE (CYC) and repressed by PERIOD (PER) and TIMELESS (TIM) [1]. The timing of CLK-CYC activation and PER-TIM repression is regulated posttranslationally, in part through rhythmic phosphorylation of CLK, PER, and TIM [[2], [3] and [4]]. Although kinases that control PER and TIM levels and subcellular localization have been identified [[5], [6], [7], [8], [9] and [10]], additional kinases are predicted to target PER, TIM, and/or CLK to promote time-specific transcriptional repression. We screened for kinases that alter circadian behavior via clock cell-directed RNA interference (RNAi) and identified the proline-directed kinase nemo (nmo) as a novel component of the circadian oscillator. Both nmo RNAi knockdown and a nmo hypomorphic mutant shorten circadian period, whereas nmo overexpression lengthens circadian period. CLK levels increase when nmo exp! ression is knocked down in clock cells, whereas CLK levels decrease and PER and TIM accumulation are delayed when nmo is overexpressed in clock cells. These data suggest that nmo slows the pace of the circadian oscillator by altering CLK, PER, and TIM expression, thereby contributing to the generation of an 24 hr circadian period.
  • Resurrecting Extinct Interactions with Extant Substitutes
    - Curr Bio 21(9):762-765 (2011)
    There is increasing evidence that restoration ecologists should be most concerned with restoring species interactions rather than species diversity per se [1]. Rewilding with taxon substitutes, the intentional introduction of exotic species to replace the ecosystem functions of recently extinct species, is one way to reverse ecosystem dysfunction following the loss of species interactions [2]. This is highly controversial [3], in part because of a lack of rigorous scientific studies [4]. Here we present the first empirical evidence of an in situ rewilding project undertaken as a hypothesis-driven ecosystem management option. On Ile aux Aigrettes, a 25-hectare island off Mauritius, the critically endangered large-fruited endemic ebony, Diospyros egrettarum (Ebenaceae), was seed-dispersal limited after the extinction of all native large-bodied frugivores, including giant tortoises. We introduced exotic Aldabra giant tortoises, Aldabrachelys gigantea, to disperse the ebon! y seeds. Not only did the tortoises ingest the large fruits and disperse substantial numbers of ebony seeds, but tortoise gut passage also improved seed germination, leading to the widespread, successful establishment of new ebony seedlings. Our results demonstrate that the introduction of these exotic frugivores is aiding the recovery of ebonies. We argue for more reversible rewilding experiments to investigate whether extinct species interactions can be restored.
  • PP1/Repo-Man Dephosphorylates Mitotic Histone H3 at T3 and Regulates Chromosomal Aurora B Targeting
    - Curr Bio 21(9):766-773 (2011)
    The transient mitotic histone H3 phosphorylation by various protein kinases regulates chromosome condensation and segregation, but the counteracting phosphatases have been poorly characterized [[1], [2], [3], [4], [5], [6], [7] and [8]]. We show here that PP1γ is the major histone H3 phosphatase acting on the mitotically phosphorylated (ph) residues H3T3ph, H3S10ph, H3T11ph, and H3S28ph. In addition, we identify Repo-Man, a chromosome-bound interactor of PP1γ [9], as a selective regulator of H3T3ph and H3T11ph dephosphorylation. Repo-Man promotes H3T11ph dephosphorylation by an indirect mechanism but directly and specifically targets H3T3ph for dephosphorylation by associated PP1γ. The PP1γ/Repo-Man complex opposes the protein kinase Haspin-mediated spreading of H3T3ph to the chromosome arms until metaphase and catalyzes the net dephosphorylation of H3T3ph at the end of mitosis. Consistent with these findings, Repo-Man modulates in a PP1-dependent manner the H3T3ph! -regulated chromosomal targeting of Aurora kinase B and its substrate MCAK. Our study defines a novel mechanism by which PP1 counteracts Aurora B.
  • Monkeys Recall and Reproduce Simple Shapes from Memory
    - Curr Bio 21(9):774-778 (2011)
    If you draw from memory a picture of the front of your childhood home, you will have demonstrated recall. You could also recognize this house upon seeing it. Unlike recognition, recall demonstrates memory for things that are not present. Recall is necessary for planning and imagining, and it can increase the flexibility of navigation, social behavior, and other cognitive skills. Without recall, memory is more limited to recognition of the immediate environment. Amnesic patients are impaired on recall tests [[1] and [2]], and recall performance often declines with aging [3]. Despite its importance, we know relatively little about nonhuman animals' ability to recall information; we lack suitable recall tests for them and depend instead on recognition tests to measure nonhuman memory. Here we report that rhesus monkeys can recall simple shapes from memory and reproduce them on a touchscreen. As in humans [[4] and [5]], monkeys remembered less in recall than recognition te! sts, and their recall performance deteriorated more slowly. Transfer tests showed that monkeys used a flexible memory mechanism rather than memorizing specific actions for each shape. Observation of recall in Old World monkeys suggests that it has been adaptive for over 30 million years [6] and does not depend on language.
  • Amphiregulin Exosomes Increase Cancer Cell Invasion
    - Curr Bio 21(9):779-786 (2011)
    Autocrine, paracrine, and juxtacrine are recognized modes of action for mammalian EGFR ligands including EGF, TGF-α (TGFα), amphiregulin (AREG), heparin-binding EGF-like growth factor (HB-EGF), betacellulin, epiregulin, and epigen. We identify a new mode of EGFR ligand signaling via exosomes. Human breast and colorectal cancer cells release exosomes containing full-length, signaling-competent EGFR ligands. Exosomes isolated from MDCK cells expressing individual full-length EGFR ligands displayed differential activities; AREG exosomes increased invasiveness of recipient breast cancer cells 4-fold over TGFα or HB-EGF exosomes and 5-fold over equivalent amounts of recombinant AREG. Exosomal AREG displayed significantly greater membrane stability than TGFα or HB-EGF. An average of 24 AREG molecules are packaged within an individual exosome, and AREG exosomes are rapidly internalized by recipient cells. Whether the composition and behavior of exosomes differ between non! transformed and transformed cells is unknown. Exosomes from DLD-1 colon cancer cells with a mutant KRAS allele exhibited both higher AREG levels and greater invasive potential than exosomes from isogenically matched, nontransformed cells in which mutant KRAS was eliminated by homologous recombination. We speculate that EGFR ligand signaling via exosomes might contribute to diverse cancer phenomena such as field effect and priming of the metastatic niche.
  • The Y-Encoded Gene Zfy2 Acts to Remove Cells with Unpaired Chromosomes at the First Meiotic Metaphase in Male Mice
    - Curr Bio 21(9):787-793 (2011)
    During male but not female mammalian meiosis, there is efficient apoptotic elimination of cells with unpaired (univalent) chromosomes at the first meiotic metaphase (MI) [1]. Apoptotic elimination of MI spermatocytes is seen in response to the univalent X chromosome of XSxraO male mice [2], in which the X chromosome carries Sxra [[3] and [4]], the Y-chromosome-derived sex-reversal factor that includes the testis determinant Sry. Sxrb is an Sxra-derived variant in which a deletion has removed six Y short-arm genes and created a Zfy2/Zfy1 fusion gene spanning the deletion breakpoint [[4] and [5]]. XSxrbO males have spermatogonial arrest that can be overcome by the re-addition of Eif2s3y from the deletion as a transgene; however, XSxrbOEif2s3y transgenic males do not show the expected elimination of MI spermatocytes in response to the univalent [6]. Here we show that these XSxrbOEif2s3y males have an impaired apoptotic response with completion of the first meiotic divisio! n, but there is no second meiotic division. We then show that Zfy2 (but not the closely related Zfy1) is sufficient to reinstate the apoptotic response to the X univalent. These findings provide further insight into the basis for the much lower transmission of chromosomal errors originating at the first meiotic division in men than in women [7].
  • Subjective Socioeconomic Status Predicts Human Ventral Striatal Responses to Social Status Information
    - Curr Bio 21(9):794-797 (2011)
    The enormous influence of hierarchical rank on social interactions [1] suggests that neural mechanisms exist to process status-related information [2] and ascribe value to it. The ventral striatum is prominently implicated in processing value and salience, independent of hedonic properties [[3] and [4]], and a functional magnetic resonance imaging (fMRI) study of social status perception in humans demonstrated that viewing higher-ranked compared to lower-ranked individuals evokes a ventral striatal response [5], indicative of a greater assignment of value/salience to higher status. Consistent with this interpretation, nonhuman primates value information associated with higher-ranked conspecifics more than lower-ranked, as illustrated using a choice paradigm in which monkeys preferentially take the opportunity to view high-status monkeys [6]. Interestingly, this status-related value assignment in nonhuman primates is influenced by one's own hierarchical rank: high-statu! s monkeys preferentially attend to conspecifics of high status, whereas low-status monkeys will also attend to other low-status monkeys [7]. Complementary to these findings, using fMRI and a social status judgment task in humans, we suggest a neurobiological mechanism by which one's own relative hierarchical rank influences the value attributed to particular social status information by demonstrating that one's subjective socioeconomic status differentially influences ventral striatal activity during processing of status-related information.
  • Box Jellyfish Use Terrestrial Visual Cues for Navigation
    - Curr Bio 21(9):798-803 (2011)
    Box jellyfish have an impressive set of 24 eyes of four different types, including eyes structurally similar to those of vertebrates and cephalopods [[1] and [2]]. However, the known visual responses are restricted to simple phototaxis, shadow responses, and object avoidance responses [[3], [4], [5], [6], [7] and [8]], and it has been a puzzle why they need such a complex set of eyes. Here we report that medusae of the box jellyfish Tripedalia cystophora are capable of visually guided navigation in mangrove swamps using terrestrial structures seen through the water surface. They detect the mangrove canopy by an eye type that is specialized to peer up through the water surface and that is suspended such that it is constantly looking straight up, irrespective of the orientation of the jellyfish. The visual information is used to navigate to the preferred habitat at the edge of mangrove lagoons.

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