Transmembrane tethering of synaptotagmin to synaptic vesicles controls multiple modes of neurotransmitter release

Synaptotagmin 1 (Syt1) is a synaptic vesicle integral membrane protein that regulates neurotransmitter release by activating fast synchronous fusion and suppressing slower asynchronous release. The cytoplasmic C2 domains of Syt1 interact with SNAREs and plasma membrane phospholipids in a Ca[superscript 2+]-dependent manner and can substitute for full-length Syt1 in in vitro membrane fusion assays. To determine whether synaptic vesicle tethering of Syt1 is required for normal fusion in vivo, we performed a structure-function study with tethering mutants at the Drosophila larval neuromuscular junction. Transgenic animals expressing only the cytoplasmic C2 domains or full-length Syt1 tethered to the plasma membrane failed to restore synchronous synaptic vesicle fusion, and also failed to clamp spontaneous vesicle release. In addition, transgenic animals with shorter, but not those with longer, linker regions separating the C2 domains from the transmembrane segment abolished Syt1’s ability to activate synchronous vesicle fusion. Similar defects were observed when C2 domain alignment was altered to C2B-C2A from the normal C2A-C2B orientation, leaving the tether itself intact. Although cytoplasmic and plasma membrane-tethered Syt1 variants could not restore synchronous release in syt1 null mutants, they were very effective in promoting fusion through the slower asynchronous pathway. As such, the subcellular localization of Syt1 within synaptic terminals is important for the temporal dynamics that underlie synchronous and asynchronous neurotransmitter release.National Institutes of Health (U.S.) (Grant NS40296)Korea (South). Ministry of Science, ICT and Future Planning (National Research Foundation of Korea. Basic Science Research Program Grant 2013R1A1A1010839

Collaborative Epistemic Discourse in Classroom Information Seeking Tasks

We discuss the relationship between information seeking, and epistemic beliefs – beliefs about the source, structure, complexity, and stability of knowledge – in the context of collaborative information seeking discourses. We further suggest that both information seeking, and epistemic cognition research agendas have suffered from a lack of attention to how information seeking as a collaborative activity is mediated by talk between partners – an area we seek to address in this paper. A small-scale observational study using sociocultural discourse analysis was conducted with eight eleven year old pupils who carried out search engine tasks in small groups. Qualitative and quantitative analysis were performed on their discussions using sociocultural discourse analytic techniques. Extracts of the dialogue are reported, informed by concordance analysis and quantitative coding of dialogue duration. We find that 1) discourse which could be characterised as ‘epistemic’ is identifiable in student talk, 2) that it is possible to identify talk which is more or less productive, and 3) that epistemic talk is associated with positive learning outcomes

Transmission, Development, and Plasticity of Synapses

Chemical synapses are sites of contact and information transfer between a neuron and its partner cell. Each synapse is a specialized junction, where the presynaptic cell assembles machinery for the release of neurotransmitter, and the postsynaptic cell assembles components to receive and integrate this signal. Synapses also exhibit plasticity, during which synaptic function and/or structure are modified in response to activity. With a robust panel of genetic, imaging, and electrophysiology approaches, and strong evolutionary conservation of molecular components, Drosophila has emerged as an essential model system for investigating the mechanisms underlying synaptic assembly, function, and plasticity. We will discuss techniques for studying synapses in Drosophila, with a focus on the larval neuromuscular junction (NMJ), a well-established model glutamatergic synapse. Vesicle fusion, which underlies synaptic release of neurotransmitters, has been well characterized at this synapse. In addition, studies of synaptic assembly and organization of active zones and postsynaptic densities have revealed pathways that coordinate those events across the synaptic cleft. We will also review modes of synaptic growth and plasticity at the fly NMJ, and discuss how pre- and postsynaptic cells communicate to regulate plasticity in response to activity

The biological function of the Huntingtin protein and its relevance to Huntington’s Disease pathology

available in PMC 2011 December 14.Huntington’s Disease is an adult-onset dominant heritable disorder characterized by progressive psychiatric disruption, cognitive deficits, and loss of motor coordination. It is caused by expansion of a polyglutamine tract within the N-terminal domain of the Huntingtin protein. The mutation confers a toxic gain-of-function phenotype, resulting in neurodegeneration that is most severe in the striatum. Increasing experimental evidence from genetic model systems such as mice, zebrafish, and Drosophila suggest that polyglutamine expansion within the Huntingtin protein also disrupts its normal biological function. Huntingtin is widely expressed during development and has a complex and dynamic distribution within cells. It is predicted to be a protein of pleiotropic function, interacting with a large number of effector proteins to mediate a host of physiological processes. In this review, we highlight the wildtype function of Huntingtin, focusing on its postdevelopmental roles in axonal trafficking, regulation of gene transcription, and cell survival. We then discuss how potential loss-of-function phenotypes resulting in polyglutamine expansion within Huntingtin may have direct relevance to the underlying pathophysiology of Huntington’s Disease.National Institutes of Health (U.S.) (NIH Grant NS052203

Pathogenic Huntington Alters BMP Signaling and Synaptic Growth through Local Disruptions of Endosomal Compartments

Huntington’s disease (HD) is a neurodegenerative disorder caused by expansion of a polyglutamine (polyQ) stretch within the Huntingtin (Htt) protein. Pathogenic Htt disrupts multiple neuronal processes, including gene expression, axonal trafficking, proteasome and mitochondrial activity, and intracellular vesicle trafficking. However, the primary pathogenic mechanism and subcellular site of action for mutant Htt are still unclear. Using a Drosophila HD model, we found that pathogenic Htt expression leads to a profound overgrowth of synaptic connections that correlates directly with the levels of Htt at nerve terminals. Branches of the same nerve containing different levels of Htt show distinct phenotypes, indicating that Htt acts locally to disrupt synaptic growth. The effects of pathogenic Htt on synaptic growth arise from defective synaptic endosomal trafficking, leading to expansion of a recycling endosomal signaling compartment containing Sorting Nexin 16 and a reduction in late endosomes containing Rab11. The disruption of endosomal compartments leads to elevated BMP signaling within nerve terminals, driving excessive synaptic growth. Blocking aberrant signaling from endosomes or reducing BMP activity ameliorates the severity of HD pathology and improves viability. Pathogenic Htt is present largely in a nonaggregated form at synapses, indicating that cytosolic forms of the protein are likely to be the toxic species that disrupt endosomal signaling. Our data indicate that pathogenic Htt acts locally at nerve terminals to alter trafficking between endosomal compartments, leading to defects in synaptic structure that correlate with pathogenesis and lethality in the Drosophila HD model.National Institutes of Health (U.S.) (Grant NS40296)National Institutes of Health (U.S.) (Grant MH104536

Synapse development in health and disease

Recent insights into the genetic basis of neurological disease have led to the hypothesis that molecular pathways involved in synaptic growth, development, and stability are perturbed in a variety of mental disorders. Formation of a functional synapse is a complex process requiring stabilization of initial synaptic contacts by adhesive protein interactions, organization of presynaptic and postsynaptic specializations by scaffolding proteins, regulation of growth by intercellular signaling pathways, reorganization of the actin cytoskeleton, and proper endosomal trafficking of synaptic growth signaling complexes. Many neuropsychiatric disorders, including autism, schizophrenia, and intellectual disability, have been linked to inherited mutations which perturb these processes. Our understanding of the basic biology of synaptogenesis is therefore critical to unraveling the pathogenesis of neuropsychiatric disorders

Comparative analysis of Drosophila and mammalian complexins as fusion clamps and facilitators of neurotransmitter release

The SNARE-binding protein complexin (Cpx) has been demonstrated to regulate synaptic vesicle fusion. Previous studies are consistent with Cpx functioning either as a synaptic vesicle fusion clamp to prevent premature exocytosis, or as a facilitator to directly stimulate release. Here we examined conserved roles of invertebrate and mammalian Cpx isoforms in the regulation of neurotransmitter release using the Drosophila neuromuscular junction as a model synapse. We find that SNARE binding by Cpx is required for its role as a fusion clamp. All four mammalian Cpx proteins (mCpx), which have been demonstrated to facilitate release, also function as fusion clamps when expressed in Drosophila cpx null mutants, though their clamping abilities vary between isoforms. Moreover, expression of mCpx I, II or III isoforms dramatically enhance evoked release compared to mCpx IV or Drosophila Cpx. Differences in the clamping and facilitating properties of complexin isoforms can be partially attributed to differences in the C-terminal membrane tethering domain. Our findings indicate that the function of complexins as fusion clamps and facilitators of fusion are conserved across evolution, and that these roles are genetically separable within an isoform and across different isoforms.National Institutes of Health (U.S.) (NIH Grant NS064750)National Institutes of Health (U.S.) (NIH Grant NS40296

JULES-BE:Representation of bioenergy crops and harvesting in the Joint UK Land Environment Simulator vn5.1

We describe developments to the land surface model JULES, allowing for flexible user-prescribed harvest regimes of various perennial bioenergy crops or natural vegetation types. Our aim is to integrate the most useful aspects of dedicated bioenergy models into dynamic global vegetation models, in order that assessment of bioenergy options can benefit from state-of-the-art Earth system modelling. A new plant functional type (PFT) representing Miscanthus is also presented. The Miscanthus PFT fits well with growth parameters observed at a site in Lincolnshire, UK; however, global observed yields of Miscanthus are far more variable than is captured by the model, primarily owing to the model's lack of representation of crop age and establishment time. Global expansion of bioenergy crop areas under a 2 ?C emissions scenario and balanced greenhouse gas mitigation strategy from the IMAGE integrated assessment model (RCP2.6- SSP2) achieves a mean yield of 4.3 billion tonnes of dry matter per year over 2040-2099, around 30 % higher than the biomass availability projected by IMAGE. In addition to perennial grasses, JULES-BE can also be used to represent short-rotation coppicing, residue harvesting from cropland or forestry and rotation forestry