EXPRESSION OF SYNAPTOTAGMIN IN DROSOPHILA REVEALS TRANSPORT AND LOCALIZATION OF SYNAPTIC VESICLES TO THE SYNAPSE

Synaptotagmin is a synaptic vesicle-specific integral membrane protein that has been suggested to play a key role in synaptic vesicle dockin g and fusion. By monitoring Synaptotagmin's cellular and subcellular d istribution during development, it is possible to study synaptic vesic le localization and transport. and synapse formation. We have initiate d the study of Synaptotagmin's expression during Drosophila neurogenes is in order to follow synaptic vesicle movement prior to and during sy napse formation, as well as to localize synaptic sites in Drosophila. In situ hybridizations to whole-mount embryos show that synaptotagmin (syt) message is present in the cell bodies of all peripheral nervous system neurons and many, if not all, central nervous system neurons du ring neurite outgrowth and synapse formation, and in mature neurons. I mmunocytochemical staining with antisera specific to Synaptotagmin ind icates that the protein is present at all stages of the Drosophila lif e cycle following germ band retraction. In embryos, Synaptotagmin is o nly transiently localized to the cell body of neurons and is transport ed rapidly along axons during axonogenesis. After synapse formation, S ynaptotagmin accumulates in a punctate pattern at all identifiable syn aptic contact sites, suggesting a general role for Synaptotagmin in sy napse function. In embryos and larvae, the most intense staining is fo und along two broad longitudinal tracts on the dorsal side of the vent ral nerve cord and the brain, and at neuromuscular junctions in the pe riphery. In the adult head, Synaptotagmin localizes to discrete region s of the neurophil where synapses are predicted to occur. These data i ndicate that synaptic vesicles are present in axons before synapse for mation, and become restricted to synaptic contact sites after synapses are formed. Since a similar expression pattern of Synaptotagmin has b een reported in mammals, we propose that the function of Synaptotagmin and the mechanisms governing localization of the synaptic vesicle bef ore and after synapse formation are conserved in invertebrate and vert ebrate species. The ability to mark synapses in Drosophila should faci litate the study of synapse formation and function, providing a new to ol to dissect the molecular mechanisms underlying these processes.