Distinct regional distribution in the brain of messenger RNAs for the two isoforms of synaphin associated with the docking/fusion complex

Synaphin is a 19,000 mol. wt cytosolic protein we first found to co- purify with the docking/fusion complex crucial to neurotransmitter release from presynaptic terminals. Two isoforms of synaphin (synaphins I and 2)(also called complexins II and I, respectively) exist in the rat brain. On density gradient centrifugation of a Triton X-100 extract of brain membranes, synaphin was found to be associated with the 7S complex that contains synaptotagmin, syntaxin, synaptosomal-associated protein of 25,000 mol. wt and vesicle-associated membrane protein. A smaller complex devoid of synaphins was also identified by immunoprecipitation with a monoclonal antibody against synaptosomal-associated protein of 25,000 mol. wt. Messenger RNAs for synaphins 1 and 2 were expressed predominantly in the brain. In situ hybridization using probes specific to synaphins 1 and 2 indicated that the distribution of their mRNAs was significantly different in brain regions such as olfactory bulb, hippocampus, cerebral cortex, piriform cortex; cerebellum, thalamus and facial nuclei. These results show synaphin as a component of the 7S complex and suggest different physiological implications for the two isoforms.