IN-VITRO EXOCYTOSIS IN SEA-URCHIN EGGS REQUIRES A SYNAPTOBREVIN-RELATED PROTEIN

Sea urchin eggs provide an efficient in vitro model of exocytosis. We have identified proteins in sea urchin eggs that cross-react with anti bodies to mammalian synaptobrevin, synaptotagmin, SNAP-25, syntaxin an d rab3a. We show that these proteins are localized to the sea urchin e gg cortex, using western blotting and immunocytochemistry. Tetanus tox in light chain cleaves the synaptobrevin-related protein in vitro and inhibits calcium-induced exocytosis. These data demonstrate a conserva tion between phyla of protein sequence and molecular mechanisms though t to facilitate exocytosis and show that the sea urchin egg provides a unique in vitro exocytotic model with which to study the conserved pr otein machinery of membrane fusion during secretion.