THE EFFECT ON SYNAPTIC PHYSIOLOGY OF SYNAPTOTAGMIN MUTATIONS IN DROSOPHILA

Synaptotagmin is a synaptic vesicle protein implicated in neurotransmi tter release. Molecular characterization of four mutant alleles of thi s protein in Drosophila melanogaster has permitted an investigation of synaptotagmin's role in synaptic physiology and of some of the struct ural requirements for its function. Reduced levels of synaptotagmin re sulted in a substantial alteration in synaptic function in the eye and at larval neuromuscular junctions. Decreased neurotransmitter release caused smaller evoked synaptic potentials. However, the frequency, bu t not the size, of spontaneous quantal events was simultaneously incre ased. These abnormalities do not appear to be secondary to a detectabl e morphological change in the arborization of the synapse. The increas ed frequency of spontaneous events was insufficient to deplete signifi cantly the vesicle supply and thereby account for reduced transmission . These data are discussed in the context of models in which synaptota gmin's function includes a role in vesicle docking.