Monday, November 22, 2010

Hot off the presses! Nov 23 curr biol

The Nov 23 issue of the curr biol is now up on Pubget (About curr biol): if you're at a subscribing institution, just click the link in the latest link at the home page. (Note you'll only be able to get all the PDFs in the issue if your institution subscribes to Pubget.)

Latest Articles Include:

  • Market forces drive biological diversity deal
    - curr biol 20(22):R953-R954 (2010)
    Providing benefits for countries holding genetic resources exploited elsewhere has been the linchpin of new biodiversity negotiations. Nigel Williams reports.
  • Red List reveals conservation pay-offs
    - curr biol 20(22):R954-R955 (2010)
    Efforts to protect species are paying off amid otherwise widespread declines. Nigel Williams reports
  • Rapid baseline changes challenge biodiversity insights
    - curr biol 20(22):R956-R957 (2010)
    Human developments, climate change and other factors present an increasing problem for efforts to conserve and protect native species. Nigel Williams reports.
  • Lights up for new Berlin natural history display
    - curr biol 20(22):R958-R959 (2010)
    Berlin's store of biological specimens are back in the limelight. Nigel Williams reports.
  • Randolph Blake
    - curr biol 20(22):R959-R961 (2010)
  • Audubon set to hit the record books
    - curr biol 20(22):R961-R962 (2010)
  • Meiotic sex chromosome inactivation
    - curr biol 20(22):R962-R963 (2010)
  • Hydra
    - curr biol 20(22):R964-R965 (2010)
  • The natural history of Caenorhabditis elegans
    - curr biol 20(22):R965-R969 (2010)
    In the laboratory, the nematode Caenorhabditis elegans lives on the surface of nutrient agar in Petri dishes, feeding on a lawn of the uracil auxotroph strain OP50, an Escherichia coli mutant strain. This sentence sums up the fundamentals of C. elegans ecology, as most of us know it. While over 15,000 articles on diverse biological aspects of C. elegans attest to the worm's undisputable virtues as a major model organism, its biology in the wild remains mysterious. To properly interpret and fully understand the available wealth of genetic, molecular and other biological observations made in the laboratory, it will be important to know its natural history and to place the species in its ecological and evolutionary context. With the aim of connecting the discoveries that have been made about C. elegans biology to its 'real life', we shall discuss recent studies on the worm's natural habitat and population biology, and outline key issues in attaining a modern natural h! istory of C. elegans.
  • Estimating human age from T-cell DNA rearrangements
    - curr biol 20(22):R970-R971 (2010)
    Predicting human phenotypes from genotypes is a newly emerging field with relevance for personalized medicine [1] and forensics [2]. However, only a few phenotypic traits can currently be identified from DNA information with accuracies sufficient for practical applications [1], most notably human eye (iris) color [3]. It could be expected that individual age is too biologically complex to allow a simple and accurate molecular estimation from biological materials. Indeed, previously proposed genetic methods for human age estimation, based on the accumulation of mitochondrial DNA deletions or on telomere shortening, show low accuracies and various technical problems, and are therefore not suitable for practical applications [4]. Proposed biochemical methods, such as those based on the accumulation of D-aspartic acid, involve the destructive analysis of specific body parts (such as bones, teeth and ligaments), and suffer from technical issues and bio-degradation [4]. In t! he present study, we demonstrate that human individual age can be estimated accurately and reliably from blood using T-cell DNA rearrangements, and we provide a robust and sensitive real-time quantitative PCR protocol for application in various areas of bioscience.
  • Sexual Dimorphism: Why the Sexes Are (and Are Not) Different
    - curr biol 20(22):R972-R973 (2010)
    Sex differences often call sexual selection to mind; however, a new damselfly study cautions on being too hasty, and implicates viability selection in the evolution of male and female colouration.
  • Vascular Lumen Formation: Negativity Will Tear Us Apart
    - curr biol 20(22):R973-R975 (2010)
    Functional blood vessels are essential for vertebrate development, but how endothelial cells initiate lumen formation during vasculogenesis is not known. A new study now reveals that electrostatic repulsion is key.
  • Numerical Processing: Stimulating Numbers
    - curr biol 20(22):R975-R977 (2010)
    A new study using transcranial direct current stimulation shows that modulating parietal cortex activity during the learning of abstract numerical material can enhance numerical competency for up to six months.
  • Evolution: Plastic Sociality in a Sweat Bee
    - curr biol 20(22):R977-R979 (2010)
    How and why do bees become social? A transplant experiment shows that sweat bees can adopt a solitary or social lifestyle in response to their environment.
  • Gene Regulation: Global Transcription Rates Scale with Size
    - curr biol 20(22):R979-R981 (2010)
    Is bigger better? Scientists have long puzzled over the potential relationship between cell size and the rate of mRNA production. A recent report builds a strong case that global transcription rates scale with size.
  • Life History: The Energy-Efficient Orangutan
    - curr biol 20(22):R981-R983 (2010)
    A study of orangutans' daily energy expenditure confirmed exceptionally slow metabolism. It suggests they evolved a lifestyle designed to minimize energy use. If so, shifting to a higher energy-use strategy may help explain how humans evolved.
  • Palaeoecology: Different Dinosaur Ecologies in Deep Time?
    - curr biol 20(22):R983-R985 (2010)
    Do dinosaurs from the Moroccan Kem Kem formation provide evidence for an ecosystem dramatically different from anything seen today? More likely the common palaeontological problem of time-averaging has had a part to play.
  • Social Evolution: War of the Worms
    - curr biol 20(22):R985-R987 (2010)
    The discovery of a non-reproductive soldier caste in a clonally reproducing trematode greatly extends the taxonomic distribution of eusociality and reaffirms the importance of relatedness in the evolution of reproductive altruism.
  • Signaling and Transcriptional Control of Reproductive Development in Arabidopsis
    - curr biol 20(22):R988-R997 (2010)
    Plant reproductive development is a complex process with diploid and haploid phases, including male and female organogenesis, meiosis, gametogenesis, pollination and fertilization. A number of regulatory mechanisms control both diploid and haploid cell division and differentiation, especially cell–cell signaling pathways mediated by receptor-linked protein kinases with prominent roles in early male development, and hormonal signaling pathways crucial for later events in male and female reproductive development. Furthermore, transcriptional networks control the proper formation of specific cell layers and embryo sac cell specification.
  • Rab-Family GTPase Regulates TOR Complex 2 Signaling in Fission Yeast
    - curr biol 20(22):1975-1982 (2010)
    Background From yeast to human, TOR (target of rapamycin) kinase plays pivotal roles in coupling extracellular stimuli to cell growth and metabolism. TOR kinase functions in two distinct protein complexes, TOR complex 1 (TORC1) and 2 (TORC2), which phosphorylate and activate different AGC-family protein kinases. TORC1 is controlled by the small GTPase Rheb, but little is known about TORC2 regulators. Results We have identified the Ryh1 GTPase, a human Rab6 ortholog, as an activator of TORC2 signaling in the fission yeast Schizosaccharomyces pombe. Mutational inactivation of Ryh1 or its guanine nucleotide exchange factor compromises the TORC2-dependent phosphorylation of the AGC-family Gad8 kinase. In addition, the effector domain of Ryh1 is important for its physical interaction with TORC2 and for stimulation of TORC2 signaling. Thus, GTP-bound Ryh1 is likely to be the active form stimulatory to TORC2-Gad8 signaling. Consistently, expression of the GTP-locked mutant Ryh1 is sufficient to promote interaction between TORC2 and Gad8 and to induce Gad8 hyperphosphorylation. The loss of functional Ryh1, TORC2, or Gad8 brings about similar vacuolar fragmentation and stress sensitivity, further corroborating their involvement in a common cellular process. Human Rab6 can substitute Ryh1 in S. pombe, and therefore Rab6 may be a potential activator of TORC2 in mammals. Conclusions In its GTP-bound form, Ryh1, an evolutionarily conserved Rab GTPase, activates TORC2 signaling to the AGC kinase Gad8. The Ryh1 GTPase and the TORC2-Gad8 pathway are required for vacuolar integrity and cellular stress resistance in S. pombe.
  • Demographic History of Oceania Inferred from Genome-wide Data
    - curr biol 20(22):1983-1992 (2010)
    Background The human history of Oceania comprises two extremes: the initial colonizations of Near Oceania, one of the oldest out-of-Africa migrations, and of Remote Oceania, the most recent expansion into unoccupied territories. Genetic studies, mostly using uniparentally inherited DNA, have shed some light on human origins in Oceania, particularly indicating that Polynesians are of mixed East Asian and Near Oceanian ancestry. Here, we use 1 million single nucleotide polymorphisms (SNPs) to investigate the demographic history of Oceania in a more detailed manner. Results We developed a new approach to account for SNP ascertainment bias, used approximate Bayesian computation simulations to choose the best-fitting model of population history, and estimated demographic parameters. We find that the ancestors of Near Oceanians diverged from ancestral Eurasians 27 thousand years ago (kya), suggesting separate initial occupations of both territories. The genetic admixture in Polynesian history between East Asians (87%) and Near Oceanians (13%) occurred 3 kya, prior to the colonization of Polynesia. Fijians are of Polynesian (65%) and additional Near Oceanian (35%) ancestry not found in Polynesians, with this admixture occurring considerably after the initial settlement of Remote Oceania. Our data support a greater contribution of East Asian women than men in the admixture history of Remote Oceania and highlight population substructure in Polynesia and New Guinea. Conclusions Despite the inherent ascertainment bias, genome-wide SNP data provide new insights into the genetic history of Oceana. Our approach to correct for ascertainment bias and obtain reliable inferences concerning demographic history should prove useful in other such studies.
  • WNT5A/JNK and FGF/MAPK Pathways Regulate the Cellular Events Shaping the Vertebrate Limb Bud
    - curr biol 20(22):1993-2002 (2010)
    Background The vertebrate limb is a classical model for understanding patterning of three-dimensional structures during embryonic development. Although decades of research have elucidated the tissue and molecular interactions within the limb bud required for patterning and morphogenesis of the limb, the cellular and molecular events that shape the limb bud itself have remained largely unknown. Results We show that the mesenchymal cells of the early limb bud are not disorganized within the ectoderm as previously thought but are instead highly organized and polarized. Using time-lapse video microscopy, we demonstrate that cells move and divide according to this orientation. The combination of oriented cell divisions and movements drives the proximal-distal elongation of the limb bud necessary to set the stage for subsequent morphogenesis. These cellular events are regulated by the combined activities of the WNT and FGF pathways. We show that WNT5A/JNK is necessary for the proper orientation of cell movements and cell division. In contrast, the FGF/MAPK signaling pathway, emanating from the apical ectodermal ridge, does not regulate cell orientation in the limb bud but instead establishes a gradient of cell velocity enabling continuous rearrangement of the cells at the distal tip of the limb. Conclusions Together, these data shed light on the cellular basis of vertebrate limb bud morphogenesis and uncover new layers to the sequential signaling pathways acting during vertebrate limb development.
  • Electrostatic Cell-Surface Repulsion Initiates Lumen Formation in Developing Blood Vessels
    - curr biol 20(22):2003-2009 (2010)
    Blood vessels function in the uptake, transport, and delivery of gases and nutrients within the body. A key question is how the central lumen of blood vessels develops within a cord of vascular endothelial cells. Here, we demonstrate that sialic acids of apical glycoproteins localize to apposing endothelial cell surfaces and generate repelling electrostatic fields within an endothelial cell cord. Both in vitro and in vivo experiments show that the negative charge of sialic acids is required for the separation of endothelial cell surfaces and subsequent lumen formation. We also demonstrate that sulfate residues can substitute for sialic acids during lumen initiation. These results therefore reveal a key step in the creation of blood vessels, the most abundant conduits in the vertebrate body. Because negatively charged mucins and proteoglycans are often found on luminal cell surfaces, it is possible that electrostatic repulsion is a general principle also used to initiat! e lumen formation in other organs.
  • A Coordinated Global Control over Cellular Transcription
    - curr biol 20(22):2010-2015 (2010)
    Although much is known about the regulation of gene transcription in eukaryotes, it is not clear whether cells have global controls that determine overall rates of transcription. We have investigated the effects that the DNA-to-protein ratio has on both total transcription and the transcription of individual genes in the unicellular eukaryote fission yeast. Mutants altered in cell size and those blocked in cell-cycle progression were used to vary the DNA-to-protein ratio over a 5-fold range. We found that cells of sizes within 2-fold of the wild-type value regulated global transcription to maintain similar transcription rates per protein regardless of the cellular DNA content. These changes in total transcription correlated with coordinated changes in gene occupancy by RNA polymerase II. In cell-cycle-arrested mutants exceeding a certain size, total transcription rates plateaued as DNA became limiting for transcription at low DNA-to-protein ratios [1]. Unexpectedly, ex! pression levels of individual genes remained tightly coordinated with each other over the entire range of cell sizes. We propose that there is a coordinated, global control that determines the rate of transcription of most genes and that this control plays a role in regulating growth rate of the cell.
  • Modulating Neuronal Activity Produces Specific and Long-Lasting Changes in Numerical Competence
    - curr biol 20(22):2016-2020 (2010)
    Around 20% of the population exhibits moderate to severe numerical disabilities [[1], [2] and [3]], and a further percentage loses its numerical competence during the lifespan as a result of stroke or degenerative diseases [4]. In this work, we investigated the feasibility of using noninvasive stimulation to the parietal lobe during numerical learning to selectively improve numerical abilities. We used transcranial direct current stimulation (TDCS), a method that can selectively inhibit or excitate neuronal populations by modulating GABAergic (anodal stimulation) and glutamatergic (cathodal stimulation) activity [[5] and [6]]. We trained subjects for 6 days with artificial numerical symbols, during which we applied concurrent TDCS to the parietal lobes. The polarity of the brain stimulation specifically enhanced or impaired the acquisition of automatic number processing and the mapping of number into space, both important indices of numerical proficiency [[7], [8] and ! [9]]. The improvement was still present 6 months after the training. Control tasks revealed that the effect of brain stimulation was specific to the representation of artificial numerical symbols. The specificity and longevity of TDCS on numerical abilities establishes TDCS as a realistic tool for intervention in cases of atypical numerical development or loss of numerical abilities because of stroke or degenerative illnesses.
  • An Evolutionarily Conserved Autoinhibitory Molecular Switch in ELMO Proteins Regulates Rac Signaling
    - curr biol 20(22):2021-2027 (2010)
    Dedicator of cytokinesis (DOCK) proteins are guanine nucleotide exchange factors (GEFs) controlling the activity of Rac1/Cdc42 during migration, phagocytosis, and myoblast fusion [[1], [2], [3] and [4]]. Engulfment and cell motility (ELMO) proteins bind a subset of DOCK members and are emerging as critical regulators of Rac signaling [[5], [6], [7], [8], [9] and [10]]. Although formation of a DOCK180/ELMO complex is not essential for Rac1 activation, ELMO mutants deficient in binding to DOCK180 are unable to promote cytoskeleton remodeling [11]. How ELMO regulates signaling through DOCK GEFs is poorly understood. Here, we identify an autoinhibitory switch in ELMO presenting homology to a regulatory unit described for Dia formins. One part of the switch, composed of a Ras-binding domain (RBD) and Armadillo repeats, is positioned N-terminally while the other is housed in the C terminus. We demonstrate interaction between these fragments, suggesting autoinhibition of ELMO! . Using a bioluminescence resonance energy transfer biosensor, we establish that ELMO undergoes conformational changes upon disruption of autoinhibition. We found that engagement of ELMO to RhoG, or with DOCK180, promotes the relief of autoinhibition in ELMO. Functionally, we found that ELMO mutants with impaired autoregulatory activity promote cell elongation. These results demonstrate an unsuspected level of regulation for Rac1 signaling via autoinhibition of ELMO.
  • Cryptic Plasticity Underlies a Major Evolutionary Transition
    - curr biol 20(22):2028-2031 (2010)
    The origin of eusociality is often regarded as a change of macroevolutionary proportions [[1] and [2]]. Its hallmark is a reproductive division of labor between the members of a society: some individuals ("helpers" or "workers") forfeit their own reproduction to rear offspring of others ("queens"). In the Hymenoptera (ants, bees, wasps), there have been many transitions in both directions between solitary nesting and sociality [[2], [3], [4] and [5]]. How have such transitions occurred? One possibility is that multiple transitions represent repeated evolutionary gains and losses of the traits underpinning sociality. A second possibility, however, is that once sociality has evolved, subsequent transitions represent selection at just one or a small number of loci controlling developmental switches between preexisting alternative phenotypes [[2] and [6]]. We might then expect transitional populations that can express either sociality or solitary nesting, depen! ding on environmental conditions. Here, we use field transplants to directly induce transitions in British and Irish populations of the sweat bee Halictus rubicundus. Individual variation in social phenotype was linked to time available for offspring production, and to the genetic benefits of sociality, suggesting that helping was not simply misplaced parental care [7]. We thereby demonstrate that sociality itself can be truly plastic in a hymenopteran.
  • Self-Serving Punishment of a Common Enemy Creates a Public Good in Reef Fishes
    - curr biol 20(22):2032-2035 (2010)
    A key challenge for evolutionary biologists is to determine conditions under which individuals benefit from a contribution to public goods [[1] and [2]]. For humans, it has been observed that punishment of free riders may promote contributions [[3] and [4]], but the conditions that lead to stable cooperation based on punishment remain hotly debated [[5], [6], [7] and [8]]. Here we present empirical evidence that public goods may emerge as a by-product of self-serving punishment in interactions between coral reef fishes and parasitic saber-tooth blennies that stealthily attack their fish victims from behind to take a bite [9]. We first show that chasing the blenny functions as punishment [10], because it decreases the probability of future attacks. We then provide evidence that in female scalefin anthias, a shoaling species, punishment creates a public good because it increases the probability that the parasite switches to another species for the next attack. A final ex! periment suggests that punishment is nevertheless self-serving because blennies appear to be able to discriminate between look-alike punishers and nonpunishers. Thus, individuals that do contribute to the public good may risk being identified by the parasite as easy targets for future attacks.
  • Intralocus Sexual Conflict Unresolved by Sex-Limited Trait Expression
    - curr biol 20(22):2036-2039 (2010)
    Sexually antagonistic selection generates intralocus sexual conflict, an evolutionary tug-of-war between males and females over optimal trait values [[1], [2], [3] and [4]]. Although the potential for this conflict is universal, the evolutionary importance of intralocus conflict is controversial because conflicts are typically thought to be resolvable through the evolution of sex-specific trait development [[1], [2], [3], [4], [5], [6], [7] and [8]]. However, whether sex-specific trait expression always resolves intralocus conflict has not been established. We assessed this with beetle populations subjected to bidirectional selection on an exaggerated sexually selected trait, the mandible. Mandibles are only ever developed in males for use in male-male combat, and larger mandibles increase male fitness (fighting [[9] and [10]] and mating success, as we show here). We find that females from populations selected for larger male mandibles have lower fitness, whereas femal! es in small-mandible populations have highest fitness, even though females never develop exaggerated mandibles. This is because mandible development changes genetically correlated characters, resulting in a negative intersexual fitness correlation across these populations, which is the unmistakable signature of intralocus sexual conflict [1]. Our results show that sex-limited trait development need not resolve intralocus sexual conflict, because traits are rarely, if ever, genetically independent of other characters [11]. Hence, intralocus conflict resolution is not as easy as currently thought.
  • A Model for Cleavage Plane Determination in Early Amphibian and Fish Embryos
    - curr biol 20(22):2040-2045 (2010)
    Current models for cleavage plane determination propose that metaphase spindles are positioned and oriented by interactions of their astral microtubules with the cellular cortex, followed by cleavage in the plane of the metaphase plate [[1] and [2]]. We show that in early frog and fish embryos, where cells are unusually large, astral microtubules in metaphase are too short to position and orient the spindle. Rather, the preceding interphase aster centers and orients a pair of centrosomes prior to nuclear envelope breakdown, and the spindle assembles between these prepositioned centrosomes. Interphase asters center and orient centrosomes with dynein-mediated pulling forces. These forces act before astral microtubules contact the cortex; thus, dynein must pull from sites in the cytoplasm, not the cell cortex as is usually proposed for smaller cells. Aster shape is determined by interactions of the expanding periphery with the cell cortex or with an interaction zone that ! forms between sister-asters in telophase. We propose a model to explain cleavage plane geometry in which the length of astral microtubules is limited by interaction with these boundaries, causing length asymmetries. Dynein anchored in the cytoplasm then generates length-dependent pulling forces, which move and orient centrosomes.
  • Actomyosin Tube Formation in Polar Body Cytokinesis Requires Anillin in C. elegans
    - curr biol 20(22):2046-2051 (2010)
    Polar body extrusion (PBE) is the specialized asymmetric division by which oocytes accomplish reduction in ploidy and retention of cytoplasm. During maternal gametogenesis, as in male meiosis and mitosis, cytokinesis is accomplished by a ring rich in active Rho, myosin, and formin-nucleated F-actin [[1], [2], [3], [4], [5], [6] and [7]]. However, unlike mitosis, wherein the contractile ring encircles the cell equator, the polar body ring assembles as a discoid cortical washer. Here we show that in Caenorhabditis elegans, the meiotic contractile ring transforms during closure from a disc above the spindle to a cylinder around the spindle midzone. The meiotic midbody tube comprises stacked cytoskeletal rings. This topological transition suggests a novel mechanism for constriction of an initially discoid cytokinetic ring. Analysis of mouse PBE indicates that midbody tube formation is a conserved process. Depletion of the scaffold protein anillin (ANI-1) from C. elegans re! sults in large and unstable polar bodies that often fuse with the oocyte. Anillin is dispensable for contractile ring assembly, initiation, and closure but is required for the meiotic contractile ring to transform from a disc into a tube. We propose that cytoskeletal bundling by anillin promotes formation of the midbody tube, which ensures the fidelity of PBE.
  • Synchronized Neural Input Shapes Stimulus Selectivity in a Collision-Detecting Neuron
    - curr biol 20(22):2052-2057 (2010)
    How higher-order sensory neurons generate complex selectivity from their simpler inputs is a fundamental question in neuroscience. The lobula giant movement detector (LGMD) is such a visual neuron in the locust Schistocerca americana that responds selectively to objects approaching on a collision course or their two-dimensional projections, looming stimuli [[1], [2], [3] and [4]]. To study how this selectivity arises, we designed an apparatus allowing us to stimulate, individually and independently, a sizable fraction of the 15,000 elementary visual inputs impinging retinotopically onto the LGMD's dendritic fan [[5], [6] and [7]] (Figure 1Ai). We then recorded intracellularly in vivo throughout the visual pathway, assessing the LGMD's activity and that of all three successive presynaptic stages conveying local excitatory inputs. Our results suggest that as collision becomes increasingly imminent, the strength of these inputs increases, whereas their latency decreases. ! This latency decrease favors summation of inputs activated sequentially throughout the looming sequence, making the neuron maximally sensitive to collision-bound trajectories. Thus, the LGMD's selectivity arises partially from presynaptic mechanisms that synchronize a large population of inputs during a looming stimulus and subsequent detection by postsynaptic mechanisms within the neuron itself. Analogous mechanisms are likely to underlie the tuning properties of visual neurons in other species as well.
  • TAp73 Acts via the bHLH Hey2 to Promote Long-Term Maintenance of Neural Precursors
    - curr biol 20(22):2058-2065 (2010)
    Increasing evidence suggests that deficits in adult stem cell maintenance cause aberrant tissue repair and premature aging [1]. While the mechanisms regulating stem cell longevity are largely unknown, recent studies have implicated p53 and its family member p63. Both proteins regulate organismal aging [[2], [3] and [4]] as well as survival and self-renewal of tissue stem cells [[5], [6], [7], [8] and [9]]. Intriguingly, haploinsufficiency for a third family member, p73, causes age-related neurodegeneration [10]. While this phenotype is at least partially due to loss of the ΔNp73 isoform, a potent neuronal prosurvival protein [[11], [12], [13], [14], [15] and [16]], a recent study showed that mice lacking the other p73 isoform, TAp73, have perturbations in the hippocampal dentate gyrus [17], a major neurogenic site in the adult brain. These findings, and the link between the p53 family, stem cells, and aging, suggest that TAp73 might play a previously unanticipated rol! e in maintenance of neural stem cells. Here, we have tested this hypothesis and show that TAp73 ensures normal adult neurogenesis by promoting the long-term maintenance of neural stem cells. Moreover, we show that TAp73 does this by transcriptionally regulating the bHLH Hey2, which itself promotes neural precursor maintenance by preventing premature differentiation.

No comments: