Showing papers by "Thomas Martin published in 2007"
TL;DR: The results suggest that CAPS/UNC-31 and UNC-13 serve parallel and dedicated roles in dense-core vesicle and synaptic vesicles exocytosis, respectively, in the C. elegans nervous system.
Abstract: Previous studies indicated that CAPS (calcium-dependent activator protein for secretion) functions as an essential component for the Ca2+-dependent exocytosis of dense-core vesicles in neuroendocrine cells. However, recent mouse knock-out studies suggested an alternative role in the vesicular uptake or storage of catecholamines. To genetically assess the functional role of CAPS, we characterized the sole Caenorhabditis elegans CAPS ortholog UNC-31 (uncoordinated family member) and determined its role in dense-core vesicle-mediated peptide secretion and in synaptic vesicle recycling. Novel assays for dense-core vesicle exocytosis were developed by expressing a prepro-atrial natriuretic factor-green fluorescent protein fusion protein in C. elegans. unc-31 mutants exhibited reduced peptide release in vivo and lacked evoked peptide release in cultured neurons. In contrast, cultured neurons from unc-31 mutants exhibited normal stimulated synaptic vesicle recycling measured by FM4-64 [N-(3-triethylammoniumpropyl)-4-(6-(4-diethylamino)phenyl)hexatrienyl)pyridinium dibromide] dye uptake. Conversely, UNC-13, which exhibits sequence homology to CAPS/UNC-31, was found to be essential for synaptic vesicle but not dense-core vesicle exocytosis. These findings indicate that CAPS/UNC-31 function is not restricted to catecholaminergic vesicles but is generally required for and specific to dense-core vesicle exocytosis. Our results suggest that CAPS/UNC-31 and UNC-13 serve parallel and dedicated roles in dense-core vesicle and synaptic vesicle exocytosis, respectively, in the C. elegans nervous system.
267 citations
TL;DR: Results provide direct evidence that Ca(2+)-dependent SNARE binding by synaptotagmin is essential for Ca( 2+)-triggered vesicle exocytosis and that Ca (2+)+)-dependent membrane binding by itself is insufficient to trigger fusion.
Abstract: Synaptotagmins contain tandem C2 domains and function as Ca2+ sensors for vesicle exocytosis but the mechanism for coupling Ca2+ rises to membrane fusion remains undefined. Synaptotagmins bind SNAREs, essential components of the membrane fusion machinery, but the role of these interactions in Ca2+-triggered vesicle exocytosis has not been directly assessed. We identified sites on synaptotagmin−1 that mediate Ca2+-dependent SNAP25 binding by zero-length cross-linking. Mutation of these sites in C2A and C2B eliminated Ca2+-dependent synaptotagmin−1 binding to SNAREs without affecting Ca2+-dependent membrane binding. The mutants failed to confer Ca2+ regulation on SNARE-dependent liposome fusion and failed to restore Ca2+-triggered vesicle exocytosis in synaptotagmin-deficient PC12 cells. The results provide direct evidence that Ca2+-dependent SNARE binding by synaptotagmin is essential for Ca2+-triggered vesicle exocytosis and that Ca2+-dependent membrane binding by itself is insufficient to trigger fusion. A structure-based model of the SNARE-binding surface of C2A provided a new view of how Ca2+-dependent SNARE and membrane binding occur simultaneously.
73 citations
TL;DR: It is found that full downregulation of synaptotagmin I and IX, which co-reside on vesicles in PC12 cells, completely abolished Ca2+-dependent vesicle exocytosis, which indicated a redundancy in function for these isoforms.
Abstract: Synaptotagmin I is considered to be a Ca2+ sensor for fast vesicle exocytosis. Because Ca2+-dependent vesicle exocytosis persists in synaptotagmin I mutants, there must be additional Ca2+ sensors. Multiple synaptotagmin isoforms co-reside on vesicles, which suggests that other isoforms complement synaptotagmin I function. We found that full downregulation of synaptotagmins I and IX, which co-reside on vesicles in PC12 cells, completely abolished Ca2+-dependent vesicle exocytosis. By contrast, Ca2+-dependent exocytosis persisted in cells expressing only synaptotagmin I or only synaptotagmin IX, which indicated a redundancy in function for these isoforms. Although either isoform was sufficient to confer Ca2+ regulation on vesicle exocytosis, synaptotagmins I and IX conferred faster and slower release rates, respectively, indicating that individual isoforms impart distinct kinetic properties to vesicle exocytosis. The downregulation of synaptotagmin I but not synaptotagmin IX impaired compensatory vesicle endocytosis, which revealed a lack of isoform redundancy and functional specialization of synaptotagmin I for endocytic retrieval.
52 citations
TL;DR: While an AZ-based regimen is associated with increased cost, the reduced rate of nephrotoxicity and availability of oral dosage forms, suggests that azoles be used preferentially over AMB, however, an increased rate of severe hepatic toxicity may be associated with VOR.
Abstract: Background
In August 2002, the antifungal prophylaxis algorithm for neutropenic hematology/oncology (NHO) patients at the Medical Center was changed from conventional amphotericin (AMB) to an azole (AZ) based regimen (fluconazole [FLU] in low-risk and voriconazole [VOR] in high-risk patients). The aim of our study was to compare outcomes associated with the two regimens, including breakthrough fungal infection, adverse drug events, and costs.
18 citations
TL;DR: This review predominantly focuses on transporters of the plastid inner envelope membrane and their roles are discussed within an overview of starch synthesis.
Abstract: Starch is synthesised and stored in plastids. In autotrophic tissues, the carbon skeletons and energy required for starch synthesis are directly available from photosynthesis. However, plastids of heterotrophic tissues require the metabolites for starch synthesis to be imported. Depending on plant species and tissue type, import is facilitated by several different plastid inner envelope metabolite transporters. Commonly, glucose-6-phosphate/phosphate translocators and adenylate translocators are used, but in the cereal endosperm, the role is carried out by ADP glucose transporters (Brittle1, BT1). This review predominantly focuses on transporters of the plastid inner envelope membrane. Their roles are discussed within an overview of starch synthesis. We also examine additional functions of these transporters according to our current knowledge.
6 citations
25 Jun 2007
TL;DR: This paper presents the use of multimodal content analysis in the MARVEL (multimodal analysis of recorded video for e-learning) project, and gives some ideas about multimodality analysis and its formalization.
Abstract: In this paper, we present the use of multimodal content analysis in the MARVEL (multimodal analysis of recorded video for e-learning) project. In this project, we record teachers giving their lectures in class and semi-automatically analyze the video-audio content in order to help transfer this lecture into a multimedia course for e-learning. We distinguish two primary goals in this application: scenario extraction (mostly from video) and content indexing (mostly from text and speech). Three objects take place in these goals: the teacher, the screen (for slide projection) and the whiteboard (for handwriting). These goals and the roles of all objects are explained in details, as well as our preliminary results. Through this application, we are giving some ideas about multimodality analysis and its formalization.
4 citations
01 Jan 2007
TL;DR: This chapter reviews recent developments in understanding the mechanisms underlying the trafficking and targeting of DCVs to, and their fusion with, the plasma membrane.
Abstract: Publisher Summary The major signaling role of neuroendocrine cells is mediated by the secretion of peptide and biogenic amine hormones Peptides, as well as amine transporters, are delivered in the Golgi to dense-core secretory vesicles (DCVs), which are conveyed to the plasma membrane where they undergo exocytic fusion triggered by Ca2+ elevations Neuroendocrine and endocrine cells rely primarily on larger DCVs (∼100–300 nm) that mediate the release of a broad array of contents, such as biogenic amines, neuropeptides, neurotrophins, and peptide hormones into the extracellular space The anterograde exocytic pathway of vesicles consists of their biogenesis, trafficking to the plasma membrane, tethering or docking at the plasma membrane, priming in preparation for fusion, and Ca2+-triggered fusion Following exocytosis, vesicles are retrieved by endocytosis and either recycled locally for Ca2+-dependent exocytosis or reclaimed by retrograde endosomal pathways Studies of the DCV exocytic pathway have been greatly facilitated by the availability of immortalized cell lines of adrenal and pancreatic P cell origin, the utility of cell lines for reverse genetic strategies, the development of permeable cell secretion systems, the exploitation of capacitance to detect DCV–plasma membrane merger, the use of amperometry to detect oxidizable content release, and the large size of DCVs for microscope imaging studies This chapter reviews recent developments in understanding the mechanisms underlying the trafficking and targeting of DCVs to, and their fusion with, the plasma membrane