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Molecular mechanisms of the biogenesis and exocytosis of regulated-secretory granules

Fertilization triggers the rapid and synchronous exocytosis of a number of secretory vesicles from the newly fertilized embryo. These vesicles deliver various components that have essential functions in the physical block of polyspermy, egg activation, and embryonic development by quickly changing the extracellular environment around the embryo. Despite the fundamental nature of these events, the molecular machinery that mediates exocytosis of these vesicles is largely unknown.
C. elegans is emerging as an amenable model system for the study of oogenesis, fertilization, and embryogenesis because all of these processes can be observed easily in a living animal. We have identified a novel type of developmentally regulated secretory granules (CAV-1 body) in C. elegans oocytes. These vesicles undergo synchronous fusion with the plasma membrane just after fertilization, as has been reported for cortical granules in other animals. We are trying to clarify the molecular mechanisms of the biogenesis and exocytosis of the cortical granules as a model of regulated secretion.