Monday, March 21, 2011

Hot off the presses! Mar 22 curr biol

The Mar 22 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:

  • Third Genetic Code Anyone?
    - curr biol 21(6):R203 (2011)
  • Riding the wave of biological data
    - curr biol 21(6):R204-R206 (2011)
    As the influx of biological data is swelling faster than the available computer capacity, scientists need to find new ways of sustainable data management. Michael Gross reports
  • Michael Dickinson
    - curr biol 21(6):R206-R207 (2011)
  • Myrmecophiles
    - curr biol 21(6):R208-R209 (2011)
  • Why should biomedical scientists care about biodiversity?
    - curr biol 21(6):R210-R211 (2011)
  • Force nanoscopy of living cells
    - curr biol 21(6):R212-R216 (2011)
    The emerging field of 'live cell nanoscopy' has revolutionized the way biologists explore the living cell at molecular resolution. Whereas far-field fluorescence nanoscopy enables the study of the nanoscale localization and dynamics of biomolecules in cells, recent developments in atomic force microscopy (AFM) techniques offer unprecedented opportunities for imaging the structural heterogeneity of cell surfaces, and for probing the functional properties of their molecular machineries (Figure 1). In the past few years, AFM-based force nanoscopy has enabled key breakthroughs in cell biology, including: deciphering the nanoscale architecture of cell surfaces and their remodelling upon changes to the cell's functional state; understanding cellular mechanics and their functional implications; quantifying the cell adhesion forces that contribute to processes like tissue development, cell division, and bacterial infection; unravelling the molecular elasticity of cellular ! proteins; and elucidating how cells reassemble membrane receptors into nanodomains and modulate their functional state. In this Primer, we explain the basic principles of AFM and provide a snapshot of some of the exciting work being done in cell biology using this multifunctional tool.
  • Invertebrate Neurobiology: Visual Direction of Arm Movements in an Octopus
    - curr biol 21(6):R217-R218 (2011)
    An operant task in which octopuses learn to locate food by a visual cue in a three-choice maze shows that they are capable of integrating visual and mechanosensory information to direct their arm movements to a goal.
  • Immunology: The Origin of Sweetbreads in Lampreys?
    - curr biol 21(6):R218-R220 (2011)
    The thymus is required for the differentiation of T lymphocytes. A new study in lampreys indicates that the pharyngeal epithelium of the gill basket supports the development of T-like cells, suggesting the existence of a primitive thymus in these oldest of vertebrates.
  • Prokaryotic Cytokinesis: Little Rings Bring Big Cylindrical Things
    - curr biol 21(6):R221-R223 (2011)
    At the division site, most bacteria assemble filaments of the tubulin homolog FtsZ that recruit other proteins into a functional divisome. A recent study describes the in vitro assembly of the divisome component SepF into small rings that organize FtsZ filaments into microtubule-like structures, possibly facilitating efficient septal growth and cytokinesis.
  • Chromatin: Bind at Your Own RSC
    - curr biol 21(6):R223-R225 (2011)
    Recent work has identified a novel RSC–nucleosome complex that both strongly phases flanking nucleosomes and presents regulatory sites for ready access. These results challenge several widely held views.
  • Animal Navigation: Longitude at Last
    - curr biol 21(6):R225-R227 (2011)
    Newly hatched sea turtles exposed to artificially generated magnetic fields with parameters characteristic of two sites 3700 km apart, differing only in longitude, can distinguish the two apparent locations and orient appropriately.
  • Autophagy: Regulation by Energy Sensing
    - curr biol 21(6):R227-R229 (2011)
    Autophagy is inhibited by the mTOR signaling pathway, which is stimulated by increased amino acid levels. When cellular energy production is compromised, AMP-activated protein kinase is activated, mTOR is inhibited and autophagy is stimulated. Two recent studies have shed light on the molecular mechanism by which AMPK controls autophagic flux.
  • Multisensory Integration: What You See Is Where You Hear
    - curr biol 21(6):R229-R231 (2011)
    Recent studies of multisensory integration compel a redefinition of fundamental sensory processes, including, but not limited to, how visual inputs influence the localization of sounds and suppression of their echoes.
  • Oogenesis: Matrix Revolutions
    - curr biol 21(6):R231-R233 (2011)
    The mechanism of egg-chamber elongation during Drosophila oogenesis has always been mysterious. A new study shows that the egg chambers spin around their long axis laying down polarised extracellular matrix, which acts as a molecular corset to restrict radial expansion.
  • Sexual Selection: Do Flies Lie with Asymmetric Legs?
    - curr biol 21(6):R233-R234 (2011)
    A newly described species of empidid or 'dance fly' shows a bizarre polymorphism in their forelegs, which presumably serve as a mating lure. This trait may have evolved by frequency-dependent deceptive male signalling.
  • Transport of Germ Plasm on Astral Microtubules Directs Germ Cell Development in Drosophila
    - curr biol 21(6):439-448 (2011)
    Background In many organisms, germ cells are segregated from the soma through the inheritance of the specialized germ plasm, which contains mRNAs and proteins that specify germ cell fate and promote germline development. Whereas germ plasm assembly has been well characterized, mechanisms mediating germ plasm inheritance are poorly understood. In the Drosophila embryo, germ plasm is anchored to the posterior cortex, and nuclei that migrate into this region give rise to the germ cell progenitors, or pole cells. How the germ plasm interacts with these nuclei for pole cell induction and is selectively incorporated into the forming pole cells is not known. Results Live imaging of two conserved germ plasm components, nanos mRNA and Vasa protein, revealed that germ plasm segregation is a dynamic process involving active transport of germ plasm RNA-protein complexes coordinated with nuclear migration. We show that centrosomes accompanying posterior nuclei induce release of germ plasm from the cortex and recruit these components by dynein-dependent transport on centrosome-nucleated microtubules. As nuclei divide, continued transport on astral microtubules partitions germ plasm to daughter nuclei, leading to its segregation into pole cells. Disruption of these transport events prevents incorporation of germ plasm into pole cells and impairs germ cell development. Conclusions Our results indicate that active transport of germ plasm is essential for its inheritance and ensures the production of a discrete population of germ cell progenitors endowed with requisite factors for germline development. Transport on astral microtubules may provide a general mechanism for the segregation of cell fate determinants.
  • EGO-1, a C. elegans RdRP, Modulates Gene Expression via Production of mRNA-Templated Short Antisense RNAs
    - curr biol 21(6):449-459 (2011)
    Background The development of the germline in Caenorhabditis elegans is a complex process involving the regulation of thousands of genes in a coordinated manner. Several genes required for small RNA biogenesis and function are among those required for the proper organization of the germline. EGO-1 is a putative RNA-directed RNA polymerase (RdRP) that is required for multiple aspects of C. elegans germline development and efficient RNA interference (RNAi) of germline-expressed genes. RdRPs have been proposed to act through a variety of mechanisms, including the posttranscriptional targeting of specific mRNAs, as well as through a direct interaction with chromatin. Despite extensive investigation, the molecular role of EGO-1 has remained enigmatic. Results Here we use high-throughput small RNA and messenger RNA sequencing to investigate EGO-1 function. We found that EGO-1 is required to produce a distinct pool of small RNAs antisense to a number of germline-expressed mRNAs through several developmental stages. These potential mRNA targets fall into distinct classes, including genes required for kinetochore and nuclear pore assembly, histone-modifying activities, and centromeric proteins. We also found several RNAi-related genes to be targets of EGO-1. Finally, we show a strong association between the loss of small RNAs and the rise of mRNA levels in ego-1(−) animals. Conclusions Our data support the conclusion that EGO-1 produces triphosphorylated small RNAs derived from mRNA templates and that these small RNAs modulate gene expression through the targeting of their cognate mRNAs.
  • Octopus vulgaris Uses Visual Information to Determine the Location of Its Arm
    - curr biol 21(6):460-462 (2011)
    Octopuses are intelligent, soft-bodied animals with keen senses that perform reliably in a variety of visual and tactile learning tasks [[1], [2], [3], [4], [5] and [6]]. However, researchers have found them disappointing in that they consistently fail in operant tasks that require them to combine central nervous system reward information with visual and peripheral knowledge of the location of their arms [[6], [7] and [8]]. Wells [6] claimed that in order to filter and integrate an abundance of multisensory inputs that might inform the animal of the position of a single arm, octopuses would need an exceptional computing mechanism, and "There is no evidence that such a system exists in Octopus, or in any other soft bodied animal." Recent electrophysiological experiments, which found no clear somatotopic organization in the higher motor centers, support this claim [9]. We developed a three-choice maze that required an octopus to use a single arm to reach a visually m! arked goal compartment. Using this operant task, we show for the first time that Octopus vulgaris is capable of guiding a single arm in a complex movement to a location. Thus, we claim that octopuses can combine peripheral arm location information with visual input to control goal-directed complex movements. 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 (29194 K)
  • Longitude Perception and Bicoordinate Magnetic Maps in Sea Turtles
    - curr biol 21(6):463-466 (2011)
    Long-distance animal migrants often navigate in ways that imply an awareness of both latitude and longitude [[1], [2] and [3]]. Although several species are known to use magnetic cues as a surrogate for latitude [[4], [5], [6], [7] and [8]], it is not known how any animal perceives longitude [[1], [9], [10] and [11]]. Magnetic parameters appear to be unpromising as longitudinal markers because they typically vary more in a north-south rather than an east–west direction [[1], [2], [9] and [10]]. Here we report, however, that hatchling loggerhead sea turtles (Caretta caretta) from Florida, USA, when exposed to magnetic fields that exist at two locations with the same latitude but on opposite sides of the Atlantic Ocean, responded by swimming in different directions that would, in each case, help them advance along their circular migratory route. The results demonstrate for the first time that longitude can be encoded into the magnetic positioning system of a migratory ! animal. Because turtles also assess north-south position magnetically [[4], [8] and [12]], the findings imply that loggerheads have a navigational system that exploits the Earth's magnetic field as a kind of bicoordinate magnetic map from which both longitudinal and latitudinal information can be extracted.
  • IQGAP-Related Rng2p Organizes Cortical Nodes and Ensures Position of Cell Division in Fission Yeast
    - curr biol 21(6):467-472 (2011)
    Correct positioning of the cell division machinery is crucial for genomic stability and cell fate determination. The fission yeast Schizosaccharomyces pombe, like animal cells, divides using an actomyosin ring and is an attractive model to study eukaryotic cytokinesis. In S. pombe, positioning of the actomyosin ring depends on the anillin-related protein Mid1p [[1], [2] and [3]]. Mid1p arrives first at the medial cortex and recruits actomyosin ring components to node-like structures [[4], [5], [6] and [7]], although how this is achieved is unknown. Here we show that the IQGAP-related protein Rng2p, an essential component of the actomyosin ring [[8] and [9]], is a key element downstream of Mid1p. Rng2p physically interacts with Mid1p and is required for the organization of other actomyosin ring components into cortical nodes. Failure of localization of Rng2p to the nodes prevents medial retention of Mid1p and leads to actomyosin ring assembly in a node-independent manne! r at nonmedial locations. We conclude that Mid1p recruits Rng2p to cortical nodes at the division site and that Rng2p, in turn, recruits other components of the actomyosin ring to cortical nodes, thereby ensuring correct placement of the division site.
  • Temporal Control of Contractile Ring Assembly by Plo1 Regulation of Myosin II Recruitment by Mid1/Anillin
    - curr biol 21(6):473-479 (2011)
    In eukaryotes, cytokinesis generally involves an actomyosin ring, the contraction of which promotes daughter cell segregation. Assembly of the contractile ring is tightly controlled in space and time [[1], [2], [3] and [4]]. In the fission yeast, contractile ring components are first organized by the anillin-like protein Mid1 into medial cortical nodes [[5], [6], [7], [8] and [9]]. These nodes then coalesce laterally into a functional contractile ring [[10], [11], [12] and [13]]. Although Mid1 is present at the medial cortex throughout G2 [14], recruitment of contractile ring components to nodes starts only at mitotic onset [12], indicating that this event is cell-cycle regulated. Polo kinases are key temporal coordinators of mitosis and cytokinesis [1], and the Polo-like kinase Plo1 is known to activate Mid1 nuclear export at mitotic onset [[15] and [16]], coupling division plane specification to nuclear position [7]. Here we provide evidence that Plo1 also triggers t! he recruitment of contractile ring components into medial cortical nodes. Plo1 binds at least two independent sites on Mid1, including a consensus site phosphorylated by Cdc2. Plo1 phosphorylates several residues within the first 100 amino acids of Mid1, which directly interact with the IQGAP Rng2 [17], and influences the timing of myosin II recruitment. Plo1 thereby facilitates contractile ring assembly at mitotic onset.
  • The Role of GABA in Human Motor Learning
    - curr biol 21(6):480-484 (2011)
    GABA modification plays an important role in motor cortical plasticity [[1], [2], [3] and [4]]. We therefore hypothesized that interindividual variation in the responsiveness of the GABA system to modification influences learning capacity in healthy adults. We assessed GABA responsiveness by transcranial direct current stimulation (tDCS), an intervention known to decrease GABA [[5] and [6]]. The magnitude of M1 GABA decrease induced by anodal tDCS correlated positively with both the degree of motor learning and the degree of fMRI signal change within the left M1 during learning. This study therefore suggests that the responsiveness of the GABAergic system to modification may be relevant to short-term motor learning behavior and learning-related brain activity.
  • Interkinetic Nuclear Migration Is a Broadly Conserved Feature of Cell Division in Pseudostratified Epithelia
    - curr biol 21(6):485-491 (2011)
    Animal development requires tight integration between the processes of proliferative growth and epithelial morphogenesis, both of which play out at the level of individual cells. In this respect, not only must polarized epithelial cells assume complex morphologies, these distinct forms must be radically and repeatedly transformed to permit mitosis. A dramatic illustration of this integration between epithelial morphogenesis and cell proliferation is interkinetic nuclear migration (IKNM), wherein the nuclei of pseudostratified epithelial cells translocate to the apical epithelial surface to execute cell division [[1] and [2]]. IKNM is widely considered a hallmark of pseudostratified vertebrate neuroepithelia, and prior investigations have proposed both actomyosin- and microtubule-dependent mechanisms for apical localization of the mitotic nucleus [[3], [4], [5], [6], [7] and [8]]. Here, using comparative functional analysis in arthropod and cnidarian systems (Drosophila! melanogaster and Nematostella vectensis), we show that actomyosin-dependent IKNM is likely to be a general feature of mitosis in pseudostratified epithelia throughout Eumetazoa. Furthermore, our studies suggest a mechanistic link between IKNM and the fundamental process of mitotic cell rounding.
  • Non-Bayesian Contour Synthesis
    - curr biol 21(6):492-496 (2011)
    Recent research has witnessed an explosive increase in models that treat percepts as optimal probabilistic inference [[1], [2], [3], [4], [5], [6], [7], [8], [9], [10], [11], [12] and [13]]. The ubiquity of partial camouflage and occlusion in natural scenes, and the demonstrated capacity of the visual system to synthesize coherent contours and surfaces from fragmented image data, has inspired numerous attempts to model visual interpolation processes as rational inference [[9], [10], [11], [12] and [13]]. Here, we report striking new forms of visual interpolation that generate highly improbable percepts. We present motion displays depicting simple occlusion sequences that elicit vivid percepts of illusory contours (ICs) in displays for which they play no necessary explanatory role. These ICs define a second, redundant occluding surface, even though all of the image data can be fully explained by an occluding surface that is clearly visible. The formation of ICs in these! images therefore entails an extraordinarily improbable co-occurrence of two occluding surfaces that arise from the same local occlusion events. The perceived strength of the ICs depends on simple low-level image properties, which suggests that they emerge as the outputs of mechanisms that automatically synthesize contours from the pattern of occlusion and disocclusion of local contour segments. These percepts challenge attempts to model visual interpolation as a form of rational inference and suggest the need to consider a broader space of computational problems and/or implementation level constraints to understand their genesis.
  • Live-Cell Imaging Reveals the Dynamics of Two Sperm Cells during Double Fertilization in Arabidopsis thaliana
    - curr biol 21(6):497-502 (2011)
    Flowering plants have evolved a unique reproductive process called double fertilization, whereby two dimorphic female gametes are fertilized by two immotile sperm cells conveyed by the pollen tube [[1] and [2]]. The two sperm cells are arranged in tandem with a leading pollen tube nucleus to form the male germ unit and are placed under the same genetic controls [3]. Genes controlling double fertilization have been identified [[4], [5] and [6]], but whether each sperm cell is able to fertilize either female gamete is still unclear [[7], [8] and [9]]. The dynamics of individual sperm cells after their release in the female tissue remain largely unknown. In this study, we photolabeled individual isomorphic sperm cells before their release and analyzed their fate during double fertilization in Arabidopsis thaliana. We found that sperm delivery was composed of three steps. Sperm cells were projected together to the boundary between the two female gametes. After a long perio! d of immobility, each sperm cell fused with either female gamete in no particular order, and no preference was observed for either female gamete. Our results suggest that the two sperm cells at the front and back of the male germ unit are functionally equivalent and suggest unexpected cell-cell communications required for sperm cells to coordinate double fertilization of the two female gametes.
  • Hepatocyte Growth Factor Acutely Perturbs Actin Filament Anchorage at the Epithelial Zonula Adherens
    - curr biol 21(6):503-507 (2011)
    Cadherin adhesion molecules function in close cooperation with the actin cytoskeleton. At the zonula adherens (ZA) of polarized epithelial cells, E-cadherin adhesion induces the cortical recruitment of many key cytoskeletal regulators, which act in a dynamic integrated system to regulate junctional integrity and cell-cell interactions [[1], [2] and [3]]. This capacity for the cytoskeleton to support the ZA carries the implication that regulators of the junctional cytoskeleton might also be targeted to perturb junctional integrity. In this report, we now provide evidence for this hypothesis. We show that hepatocyte growth factor (HGF), which is well-known to disrupt cell-cell interactions, acutely perturbs ZA integrity much more rapidly than generally appreciated. This is accompanied by significant loss of junctional F-actin, a process that reflects loss of filament anchorage at the junctions. We demonstrate that this involves uncoupling of the unconventional motor myos! in VI from junctional E-cadherin, a novel effect of HGF that is mediated by intracellular calcium. We conclude that regulators of the junctional cytoskeleton are likely to be major targets for cadherin junctions to be acutely modulated in development and perturbed in disease.
  • The AP2/ERF Transcription Factor WIND1 Controls Cell Dedifferentiation in Arabidopsis
    - curr biol 21(6):508-514 (2011)
    Many multicellular organisms have remarkable capability to regenerate new organs after wounding. As a first step of organ regeneration, adult somatic cells often dedifferentiate to reacquire cell proliferation potential, but mechanisms underlying this process remain unknown in plants. Here we show that an AP2/ERF transcription factor, WOUND INDUCED DEDIFFERENTIATION 1 (WIND1), is involved in the control of cell dedifferentiation in Arabidopsis. WIND1 is rapidly induced at the wound site, and it promotes cell dedifferentiation and subsequent cell proliferation to form a mass of pluripotent cells termed callus. We further demonstrate that ectopic overexpression of WIND1 is sufficient to establish and maintain the dedifferentiated status of somatic cells without exogenous auxin and cytokinin, two plant hormones that are normally required for cell dedifferentiation [1]. In vivo imaging of a synthetic cytokinin reporter [2] reveals that wounding upregulates the B-type ARABI! DOPSIS RESPONSE REGULATOR (ARR)-mediated cytokinin response and that WIND1 acts via the ARR-dependent signaling pathway to promote cell dedifferentiation. This study provides novel molecular insights into how plants control cell dedifferentiation in response to wounding.
  • Hosts Improve the Reliability of Chick Recognition by Delaying the Hatching of Brood Parasitic Eggs
    - curr biol 21(6):515-519 (2011)
    The reliability of information that animals use to make decisions has fitness consequences. Accordingly, selection should favor the evolution of strategies that enhance the reliability of information used in learning and decision making. For example, hosts of avian brood parasites should be selected to increase the reliability of the information they use to learn to recognize their own eggs and chicks [[1], [2] and [3]]. The American coot (Fulica americana), a conspecific brood parasite, uses cues learned from the first-hatched chicks of each brood to recognize and reject parasitic chicks [3]. However, if parasitic eggs are among the first to hatch, recognition cues are confounded and parents then fail to distinguish parasitic chicks from their own chicks. Therefore, hosts could ensure correct chick recognition by delaying parasitic eggs from hatching until after the first host eggs. Here we demonstrate that discriminatory incubation, whereby coots specifically delay t! he hatching of parasitic eggs, improves the reliability of parasitic chick recognition. In effect, coots gain fitness benefits by enhancing the reliability of information they later use for learning. Our study shows that a positive interaction between two host adaptations in coots—egg recognition and chick recognition—increases the overall effectiveness of host defense.
  • The AFB4 Auxin Receptor Is a Negative Regulator of Auxin Signaling in Seedlings
    - curr biol 21(6):520-525 (2011)
    The plant hormone auxin is perceived by a family of F box proteins called the TIR1/auxin-signaling F box proteins (AFBs). Phylogenetic studies reveal that these proteins fall into four clades in flowering plants called TIR1, AFB2, AFB4, and AFB6 [1]. Genetic studies indicate that members of the TIR1 and AFB2 groups act as positive regulators of auxin signaling [[1] and [2]]. In this report, we demonstrate a unique role for the AFB4 clade. Both AFB4 and AFB5 function as auxin receptors based on in vitro assays. However, unlike other members of the family, loss of AFB4 results in a range of growth defects that are consistent with auxin hypersensitivity, including increased hypocotyl and petiole elongation and increased numbers of lateral roots. Indeed, qRT-PCR experiments show that afb4-2 is hypersensitive to indole-3-acetic acid (IAA) in the hypocotyl, indicating that AFB4 is a negative regulator of auxin response. Furthermore, we show that AFB4 has a particularly impor! tant role in the response of seedlings to elevated temperature. Finally, we provide evidence that the AFB4 clade is the major target of the picloram family of auxinic herbicides. These results reveal a previously unknown aspect of auxin receptor function.
  • Repeated colonization and hybridization in Lake Malawi cichlids
    - curr biol 21(6):526 (2011)

No comments: