Monday, July 25, 2011

Hot off the presses! Jul 26 Curr Biol

The Jul 26 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:

  • Valuing Nature
    - Curr Biol 21(14):R525-R527 (2011)
    After decades of environmentalist campaigning, businesses still pollute and destroy the natural environment because these 'externalities' don't enter their balance sheets. Now politicians, NGOs, academics and business leaders are coming together to save what remains of the natural environment by working out just how valuable it is for us. Michael Gross reports.
  • Electric fish
    - Curr Biol 21(14):R528-R529 (2011)
  • Desmosomes
    - Curr Biol 21(14):R529-R531 (2011)
  • Laurent Keller
    - Curr Biol 21(14):R532-R533 (2011)
  • Phagocytosis
    - Curr Biol 21(14):R533-R538 (2011)
    Phagocytosis is defined as the receptor-mediated engulfment of large (≥0.5 μm) particles into plasma membrane-derived vacuoles called phagosomes. Following scission from the plasma membrane, the phagosomes undergo a maturation process, sequentially fusing with endosomes and lysosomes, ultimately becoming phagolysosomes — highly acidic and hydrolase-rich organelles that degrade the internalized particles. This brief description is a gross oversimplification of a highly complex and precisely choreographed process. Indeed, phagosome formation and maturation have emerged as paradigms to investigate many key questions in cell biology, including signal transduction, cytoskeletal remodeling, membrane dynamics and trafficking, and even gene expression.
  • Brief periods of monocular deprivation disrupt ocular balance in human adult visual cortex
    - Curr Biol 21(14):R538-R539 (2011)
    Neuroplasticity is a fundamental property of the developing mammalian visual system, with residual potential in adult human cortex [1]. A short period of abnormal visual experience (such as occlusion of one eye) before closure of the critical period has dramatic and permanent neural consequences, reshaping visual cortical organization in favour of the non-deprived eye [2] and [3]. We used binocular rivalry [4] — a sensitive probe of neural competition — to demonstrate that adult human visual cortex retains a surprisingly high degree of neural plasticity, with important perceptual consequences. We report that 150 minutes of monocular deprivation strongly affects the dynamics of binocular rivalry, unexpectedly causing the deprived eye to prevail in conscious perception twice as much as the non-deprived eye, with significant effects for up to 90 minutes. Apparent contrast of stimuli presented to the deprived eye was also increased, suggesting that the deprivation acts! by up-regulation of cortical gain-control mechanisms of the deprived eye. The results suggest that adult visual cortex retains a good deal of plasticity that could be important in reaction to sensory loss.
  • Stomata: Active Portals for Flourishing on Land
    - Curr Biol 21(14):R540-R541 (2011)
    Two studies suggest early land plants could actively control stomata, facilitating gas exchange while limiting water loss, a critical adaption to life on land.
  • Gene Regulation: Piecing Together the Puzzle of Enhancer Evolution
    - Curr Biol 21(14):R542-R543 (2011)
    The sequences of some gene regulatory elements diverge considerably, even between closely related species. A detailed analysis of the fast-evolving sparkling enhancer in Drosophila now identifies key compensatory mechanisms and 'grammar' elements that are critical for maintaining functional integrity.
  • Speech Perception: A Language-Trained Chimpanzee Weighs In
    - Curr Biol 21(14):R543-R546 (2011)
    A language-trained chimpanzee is able to interpret synthetic 'auditory caricatures' as speech. Important components of human speech perception thus rely upon general auditory mechanisms that predated the evolution of spoken language.
  • Seed Dispersal: Same Gene, Different Organs
    - Curr Biol 21(14):R546-R548 (2011)
    A single nucleotide change in a conserved promoter element is responsible for both human-selected retention of rice grains on pedicels and for naturally selected differences in dehiscence-associated fruit structures in mustards.
  • Inflammation: Cell Recruitment versus Local Proliferation
    - Curr Biol 21(14):R548-R550 (2011)
    Inflammation leads to local accumulation of macrophages. A new study shows that macrophage accumulation in inflammatory reactions dominated by type 2 immune responses is a result of local cell proliferation as opposed to recruitment of monocytes from the blood.
  • Mycorrhizal Symbioses: How to Be Seen as a Good Fungus
    - Curr Biol 21(14):R550-R552 (2011)
    Plants continually encounter many microorganisms. Some are good, but many are bad. Two studies show how beneficial fungi tell the plant to let them in and how the fungus avoids setting off the plant's defense reaction.
  • Cell Biology: Actin Keeps Endocytosis on a Short Leash
    - Curr Biol 21(14):R552-R554 (2011)
    High-resolution structural analysis of branched actin networks at the sites of clathrin-mediated endocytosis sheds light on the role of actin in endocytosis and mechanisms controlling actin assembly.
  • Plant Genomics: Homoplasy Heaven in a Lycophyte Genome
    - Curr Biol 21(14):R554-R556 (2011)
    The recent genomic sequencing of Selaginella, a member of the lycophyte lineage of vascular plants, opens up all kinds of new opportunities to examine the patterns of evolutionary innovation and the creation of the basic bauplan of plants.
  • Cell Division: Aurora B Illuminates a Checkpoint Pathway
    - Curr Biol 21(14):R557-R559 (2011)
    Separating mitotic error correction, chromosome biorientation and the spindle assembly checkpoint (SAC) is complicated by their interconnected relationships. New research finds that Aurora B kinase, which drives error correction and promotes biorientation, also directly regulates the SAC.
  • Building Distinct Actin Filament Networks in a Common Cytoplasm
    - Curr Biol 21(14):R560-R569 (2011)
    Eukaryotic cells generate a diversity of actin filament networks in a common cytoplasm to optimally perform functions such as cell motility, cell adhesion, endocytosis and cytokinesis. Each of these networks maintains precise mechanical and dynamic properties by autonomously controlling the composition of its interacting proteins and spatial organization of its actin filaments. In this review, we discuss the chemical and physical mechanisms that target distinct sets of actin-binding proteins to distinct actin filament populations after nucleation, resulting in the assembly of actin filament networks that are optimized for specific functions.
  • Structural Organization of the Actin Cytoskeleton at Sites of Clathrin-Mediated Endocytosis
    - Curr Biol 21(14):1167-1175 (2011)
    Background The dynamic actin cytoskeleton plays an important role in clathrin-mediated endocytosis (CME). However, its exact functions remain uncertain as a result of a lack of high-resolution structural information regarding actin architecture at endocytic sites. Results Using platinum replica electron microscopy in combination with electron tomography, we found that actin patches associated with clathrin-coated structures (CCSs) in cultured mouse cells consist of a densely branched actin network, in which actin filament barbed ends are oriented toward the CCS. The shape of the actin network varied from a small lateral patch at the periphery of shallow CCSs, to a collar-like arrangement around partly invaginated CCSs with actin filament barbed ends abutting the CCS neck, to a polarized comet tail in association with highly constricted or fully endocytosed CCSs. Conclusions Our data suggest that the primary role of the actin cytoskeleton in CME is to constrict and elongate the bud neck and drive the endocytosed vesicles from the plasma membrane. Moreover, in these processes, barbed ends directly push onto the load, as in a conventional propulsion mechanism. Based on our findings, we propose a model for initiation, evolution, and function of the dendritic actin network at CCSs.
  • Rhythmic TMS Causes Local Entrainment of Natural Oscillatory Signatures
    - Curr Biol 21(14):1176-1185 (2011)
    Background Neuronal elements underlying perception, cognition, and action exhibit distinct oscillatory phenomena, measured in humans by electro- or magnetoencephalography (EEG/MEG). So far, the correlative or causal nature of the link between brain oscillations and functions has remained elusive. A compelling demonstration of causality would primarily generate oscillatory signatures that are known to correlate with particular cognitive functions and then assess the behavioral consequences. Here, we provide the first direct evidence for causal entrainment of brain oscillations by transcranial magnetic stimulation (TMS) using concurrent EEG. Results We used rhythmic TMS bursts to directly interact with an MEG-identified parietal α-oscillator, activated by attention and linked to perception. With TMS bursts tuned to its preferred α-frequency (α-TMS), we confirmed the three main predictions of entrainment of a natural oscillator: (1) that α-oscillations are induced during α-TMS (reproducing an oscillatory signature of the stimulated parietal cortex), (2) that there is progressive enhancement of this α-activity (synchronizing the targeted, α-generator to the α-TMS train), and (3) that this depends on the pre-TMS phase of the background α-rhythm (entrainment of natural, ongoing α-oscillations). Control conditions testing different TMS burst profiles and TMS-EEG in a phantom head confirmed specificity of α-boosting to the case of synchronization between TMS train and neural oscillator. Conclusions The periodic electromagnetic force that is generated during rhythmic TMS can cause local entrainment of natural brain oscillations, emulating oscillatory signatures activated by cognitive tasks. This reveals a new mechanism of online TMS action on brain activity and can account for frequency-specific behavioral TMS effects at the level of biologically relevant rhythms.
  • Rapid Evolutionary Rewiring of a Structurally Constrained Eye Enhancer
    - Curr Biol 21(14):1186-1196 (2011)
    Background Enhancers are genomic cis-regulatory sequences that integrate spatiotemporal signals to control gene expression. Enhancer activity depends on the combination of bound transcription factors as well as—in some cases—the arrangement and spacing of binding sites for these factors. Here, we examine evolutionary changes to the sequence and structure of sparkling, a Notch/EGFR/Runx-regulated enhancer that activates the dPax2 gene in cone cells of the developing Drosophila eye. Results Despite functional and structural constraints on its sequence, sparkling has undergone major reorganization in its recent evolutionary history. Our data suggest that the relative strengths of the various regulatory inputs into sparkling change rapidly over evolutionary time, such that reduced input from some factors is compensated by increased input from different regulators. These gains and losses are at least partly responsible for the changes in enhancer structure that we observe. Furthermore, stereotypical spatial relationships between certain binding sites ("grammar elements") can be identified in all sparkling orthologs—although the sites themselves are often recently derived. We also find that low binding affinity for the Notch-regulated transcription factor Su(H), a conserved property of sparkling, is required to prevent ectopic responses to Notch in noncone cells. Conclusions Rapid DNA sequence turnover does not imply either the absence of critical cis-regulatory information or the absence of structural rules. Our findings demonstrate that even a severely constrained cis-regulatory sequence can be significantly rewired over a short evolutionary timescale.
  • A Secreted Effector Protein of Laccaria bicolor Is Required for Symbiosis Development
    - Curr Biol 21(14):1197-1203 (2011)
    Soil-borne mutualistic fungi, such as the ectomycorrhizal fungi, have helped shape forest communities worldwide over the last 180 million years through a mutualistic relationship with tree roots in which the fungal partner provides a large array of nutrients to the plant host in return for photosynthetically derived sugars [[1] and [2]]. This exchange is essential for continued growth and productivity of forest trees, especially in nutrient-poor soils. To date, the signals from the two partners that mediate this symbiosis have remained uncharacterized. Here we demonstrate that MYCORRHIZAL iNDUCED SMALL SECRETED PROTEIN 7 (MiSSP7), the most highly symbiosis-upregulated gene from the ectomycorrhizal fungus Laccaria bicolor [3], encodes an effector protein indispensible for the establishment of mutualism. MiSSP7 is secreted by the fungus upon receipt of diffusible signals from plant roots, imported into the plant cell via phosphatidylinositol 3-phosphate-mediated endocyto! sis, and targeted to the plant nucleus where it alters the transcriptome of the plant cell. L. bicolor transformants with reduced expression of MiSSP7 do not enter into symbiosis with poplar roots. MiSSP7 resembles effectors of pathogenic fungi, nematodes, and bacteria that are similarly targeted to the plant nucleus to promote colonization of the plant tissues [[4], [5], [6], [7], [8] and [9]] and thus can be considered a mutualism effector.
  • A Secreted Fungal Effector of Glomus intraradices Promotes Symbiotic Biotrophy
    - Curr Biol 21(14):1204-1209 (2011)
    Biotrophic fungi interacting with plants establish long-term relationships with their hosts to fulfill their life cycles. In contrast to necrotrophs, they need to contend with the defense mechanisms of the plant to develop within the host and feed on living cells [1]. It is generally accepted that microbial pathogens produce and deliver a myriad of effector proteins to hijack the cellular program of their hosts [[1], [2], [3], [4] and [5]]. Arbuscular mycorrhizal (AM) fungi are the most widespread biotrophs of plant roots [6]. We investigated whether AM fungi use effector proteins to short-circuit the plant defense program. Here we show that Glomus intraradices secretes a protein, SP7, that interacts with the pathogenesis-related transcription factor ERF19 in the plant nucleus. ERF19 is highly induced in roots by the fungal pathogen Colletotrichum trifolii as well as by several fungal extracts, but only transiently during mycorrhiza colonization. When constitutively ex! pressed in roots, SP7 leads to higher mycorrhization while reducing the levels of C. trifolii-mediated defense responses. Furthermore, expression of SP7 in the rice blast fungus Magnaporthe oryzae attenuates root decay symptoms. Taken together, these results suggest that SP7 is an effector that contributes to develop the biotrophic status of AM fungi in roots by counteracting the plant immune program.
  • A Chimpanzee Recognizes Synthetic Speech with Significantly Reduced Acoustic Cues to Phonetic Content
    - Curr Biol 21(14):1210-1214 (2011)
    A long-standing debate concerns whether humans are specialized for speech perception [[1], [2], [3], [4], [5], [6] and [7]], which some researchers argue is demonstrated by the ability to understand synthetic speech with significantly reduced acoustic cues to phonetic content [[2], [3], [4] and [7]]. We tested a chimpanzee (Pan troglodytes) that recognizes 128 spoken words [[8] and [9]], asking whether she could understand such speech. Three experiments presented 48 individual words, with the animal selecting a corresponding visuographic symbol from among four alternatives. Experiment 1 tested spectrally reduced, noise-vocoded (NV) synthesis, originally developed to simulate input received by human cochlear-implant users [10]. Experiment 2 tested "impossibly unspeechlike" [3] sine-wave (SW) synthesis, which reduces speech to just three moving tones [11]. Although receiving only intermittent and noncontingent reward, the chimpanzee performed well above chance level,! including when hearing synthetic versions for the first time. Recognition of SW words was least accurate but improved in experiment 3 when natural words in the same session were rewarded. The chimpanzee was more accurate with NV than SW versions, as were 32 human participants hearing these items. The chimpanzee's ability to spontaneously recognize acoustically reduced synthetic words suggests that experience rather than specialization is critical for speech-perception capabilities that some have suggested are uniquely human [[12], [13] and [14]].
  • The Same Regulatory Point Mutation Changed Seed-Dispersal Structures in Evolution and Domestication
    - Curr Biol 21(14):1215-1219 (2011)
    It is unclear whether gene regulatory changes that drive evolution at the population and species levels [[1], [2] and [3]] can be extrapolated to higher taxonomic levels [[4] and [5]]. Here, we investigated the role of cis-regulatory changes in fruit evolution within the Brassicaceae family. REPLUMLESS (RPL, At5g02030) controls development of the replum, a structure with an important role in fruit opening and seed dispersal [6]. We show that reduced repla resembling the Arabidopsis rpl mutant correlated across the Brassicaceae with a point mutation in a conserved cis-element of RPL. When introduced in Arabidopsis, this nucleotide change specifically reduced RPL expression and function in the fruit. Conversely, Brassica RPL containing the Arabidopsis version of the cis-element was sufficient to convert the Brassica replum to an Arabidopsis-like morphology. A mutation in the same nucleotide position of the same cis-element in a RPL ortholog has been independently selecte! d to reduce seed dispersal during domestication of rice [7], in spite of its very different fruit anatomy. Thus, single-nucleotide regulatory mutations at the same position explain developmental variation in seed-dispersal structures at the population and family levels and suggest that the same genetic toolkit is relevant to domestication and natural evolution in widely diverged species.
  • Early Specialization for Voice and Emotion Processing in the Infant Brain
    - Curr Biol 21(14):1220-1224 (2011)
    Human voices play a fundamental role in social communication, and areas of the adult "social brain" show specialization for processing voices and their emotional content (superior temporal sulcus, inferior prefrontal cortex, premotor cortical regions, amygdala, and insula) [[1], [2], [3], [4], [5], [6], [7] and [8]]. However, it is unclear when this specialization develops. Functional magnetic resonance (fMRI) studies suggest that the infant temporal cortex does not differentiate speech from music or backward speech [[9] and [10]], but a prior study with functional near-infrared spectroscopy revealed preferential activation for human voices in 7-month-olds, in a more posterior location of the temporal cortex than in adults [11]. However, the brain networks involved in processing nonspeech human vocalizations in early development are still unknown. To address this issue, in the present fMRI study, 3- to 7-month-olds were presented with adult nonspeech vocalizations ! (emotionally neutral, emotionally positive, and emotionally negative) and nonvocal environmental sounds. Infants displayed significant differential activation in the anterior portion of the temporal cortex, similarly to adults [1]. Moreover, sad vocalizations modulated the activity of brain regions involved in processing affective stimuli such as the orbitofrontal cortex [12] and insula [[7] and [8]]. These results suggest remarkably early functional specialization for processing human voice and negative emotions.
  • Notch-Dependent Induction of Left/Right Asymmetry in C. elegans Interneurons and Motoneurons
    - Curr Biol 21(14):1225-1231 (2011)
    Although nervous systems are largely bilaterally symmetric on a structural level, they display striking degrees of functional left/right (L/R) asymmetry. In Caenorhabditis elegans, two structurally symmetric pairs of sensory neurons, ASE and AWC, display two distinctly controlled types of functional L/R asymmetries (stereotyped versus stochastic asymmetry) [[1], [2] and [3]]. Beyond these two cases, the extent of neuronal asymmetry in the C. elegans nervous system was unclear. Here, we report that the Beta3/Olig-type bHLH transcription factor hlh-16 is L/R asymmetrically expressed in several distinct, otherwise bilaterally symmetric interneuron and motoneuron pairs that are part of a known navigation circuit. We find that hlh-16 asymmetry is generated during gastrulation by an asymmetric LAG-2/Delta signal originating from the mesoderm that promotes hlh-16 expression in neurons on the left side through direct binding of the Notch effector LAG-1/Su(H)/CBF to a cis-regul! atory element in the hlh-16 locus. Removal of hlh-16 reveals an unanticipated asymmetry in the ability of the axons of the AIY interneurons to extend into the nerve ring, with the left AIY axon requiring elevated hlh-16 expression for correct extension. Our study suggests that the extent of molecular L/R asymmetry in the C. elegans nervous system is broader than previously anticipated, establishes a novel signaling mechanism that crosses germ layers to diversify bilaterally symmetric neuronal lineages, and reveals L/R asymmetric control of axonal outgrowth of bilaterally symmetric neurons.
  • FLOWERING LOCUS T Regulates Stomatal Opening
    - Curr Biol 21(14):1232-1238 (2011)
    Stomatal pores surrounded by a pair of guard cells in the plant epidermis control gas exchange for photosynthesis in response to light, CO2, and phytohormone abscisic acid [[1] and [2]]. Phototropins (phot1 and phot2) are plant blue-light receptor kinases and mediate stomatal opening via activation of the plasma membrane H+-ATPase [[3] and [4]]. However, the signaling mechanism from phototropins to the H+-ATPase has yet to be determined. Here, we show that FLOWERING LOCUS T (FT) is expressed in guard cells and regulates stomatal opening. We isolated an scs (suppressor of closed-stomata phenotype in phot1 phot2) 1-1 mutant of Arabidopsis thaliana and showed that scs1-1 carries a novel null early flowering 3 (elf3) allele in a phot1 phot2 background. scs1-1 (elf3 phot1 phot2 triple mutant) had an open-stomata phenotype with high H+-ATPase activity and showed increased levels of FT mRNA in guard cells. Transgenic plants overexpressing FT in guard cells showed open stomata! , whereas a loss-of-function FT allele, ft-1, exhibited closed stomata and failed to activate the H+-ATPase in response to blue light. Our results define a new cell-autonomous role for FT and demonstrate that the flowering time genes ELF3 and FT are involved in the regulation of H+-ATPase by blue light in guard cells.
  • Kinesin-3 KLP-6 Regulates Intraflagellar Transport in Male-Specific Cilia of Caenorhabditis elegans
    - Curr Biol 21(14):1239-1244 (2011)
    Cilia are cellular sensory organelles whose integrity of structure and function are important to human health [1]. All cilia are assembled and maintained by kinesin-2 motors in a process termed intraflagellar transport (IFT), but they exhibit great variety of morphology and function. This diversity is proposed to be conferred by cell-specific modulation of the core IFT by additional factors, but examples of such IFT modulators are limited [[2], [3] and [4]]. Here we demonstrate that the cell-specific kinesin-3 KLP-6 acts as a modulator of both IFT dynamics and length in the cephalic male (CEM) cilia of Caenorhabditis elegans. Live imaging of GFP-tagged kinesins in CEM cilia shows partial uncoupling of the IFT motors of the kinesin-2 family, kinesin-II and OSM-3/KIF17, with a portion of OSM-3 moving independently of the IFT complex. KLP-6 moves independently of the kinesin-2 motors and acts to reduce the velocity of OSM-3 and IFT. Additionally, kinesin-II mutants displa! y a novel CEM cilia elongation phenotype that is partially dependent on OSM-3 and KLP-6. Our observations illustrate modulation of the general kinesin-2-driven IFT process by a cell-specific kinesin-3 in cilia of C. elegans male neurons.
  • UBAP1 Is a Component of an Endosome-Specific ESCRT-I Complex that Is Essential for MVB Sorting
    - Curr Biol 21(14):1245-1250 (2011)
    Endosomal sorting complexes required for transport (ESCRTs) regulate several events involving membrane invagination, including multivesicular body (MVB) biogenesis, viral budding, and cytokinesis [1]. In each case, upstream ESCRTs combine with additional factors, such as Bro1 proteins [[2], [3] and [4]], to recruit ESCRT-III and the ATPase VPS4 in order to drive membrane scission [5]. A clue to understanding how such diverse cellular processes might be controlled independently of each other has been the identification of ESCRT isoforms. Mammalian ESCRT-I comprises TSG101, VPS28, VPS37A–D [[6], [7] and [8]], and MVB12A/B [9]. These could generate several ESCRT-I complexes, each targeted to a different compartment and able to recruit distinct ESCRT-III proteins. Here we identify a novel ESCRT-I component, ubiquitin-associated protein 1 (UBAP1), which contains a region conserved in MVB12 [10]. UBAP1 binds the endosomal Bro1 protein His domain protein tyrosine phosphatas! e (HDPTP) [4], but not Alix, a Bro1 protein involved in cytokinesis [[11] and [12]]. UBAP1 is required for sorting EGFR to the MVB and for endosomal ubiquitin homeostasis, but not for cytokinesis. UBAP1 is part of a complex that contains a fraction of total cellular TSG101 and that also contains VPS37A but not VPS37C. Hence, the presence of UBAP1, in combination with VPS37A, defines an endosome-specific ESCRT-I complex.

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