It became possible several years ago to purify synaptic vesicles in reasonable yield and with high purity from the electric organ of fish. Because of a lack of suitable markers synaptic vesicles demonstrated to have similar purity could not be obtained from mammalian brain. We have discovered an antigen, SV2, that is present in synaptic vesicles in electric fish and also in the mammalian peripheral and central nervous system. Another antigen, SV4, is an intravesicular proteoglycan that carries pathway-specific antigens, also found in the synaptic cleft. in this funding period we will use the SV2 antigen as a marker to ask if a newly-synthesized synaptic vesicle membrane protein is targeted directly to the synaptic vesicle, and if so where the address information lies. We will also use the SV2 antigen to purify mammalian brain synaptic vesicles to look for other proteins common to all vesicles. With antibodies to the shared proteins of mammalian synaptic vesicles, it will become possible to explore the function of the proteins by generating mutants in exocytosis, by microinjection of antibodies, and by an in vitro reconstitution of fast axonal transport that we have recently developed. The synapse-specific antigen we have discovered (SV4) is not found in mammalian nerve terminals. To ask if in mammalian systems synaptic vesicles contribute unique proteoglycans to the synaptic junction, we will generate monoclonal antibodies to vesicle and synaptic junction proteoglycans from mammalian brain. We will be looking for a unique proteoglycan that travels by fast axonal transport, is found in synaptic vesicles and becomes a component of the synaptic junctional complex.
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