Molecular composition of transmitter release site and the mechanism of synaptic vesicle tethering

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Recent studies have paved the way for the elucidation of the molecular mechanisms of neurotransmitter release. However, many aspects of the molecular composition and synaptic vesicle tethering mechanisms of the release site remain unsolved. In this research, we first studied the mechanism of action of the cytosolic protein synaphin in the release mechanisms. By injecting a peptide that constitute the synaphin binding site to syntaxin into the squid giant presynaptic terminal, we have shown that synaphin is essential for the fast release of neurotransmitter molecules. Our results suggest that the protein act by facilitating oligomerization of SNARE complexes. Synaphin probably acts just before fusion.The study on mGluR7 binding proteins is still underway. We have not yet succeeded in obtaining full-length cDNA clones for these proteins. The mRNAs for these proteins are probably very liable to degradation.To understand the mechanisms for synaptic vesicle localization at the release site at the internal surface of the plasma membrane in the nerve terminal we have used the neuromuscular junction of Drosophila larva. Our findings indicate that unlike the reserve pool of synaptic vesicles which involves the synaptic vesicle protein synapsin, the cytoskeletal protein tubulin is important for the formation of the readily releasable pool. The dynamic movement of tubulin structures in the nerve terminal was unambiguously demonstrated by immunohistochemical staining. Our results suggest an important role for microtubules in the nerve terminal.