Molecular Mechanisms of Neurotransmitter Release
Communication within the nervous system involves neurotransmitter release from synaptic vesicles that fuse with the presynaptic membrane following a calcium influx during an action potential. The biochemical and molecular events underlying neurotransmitter release and the trafficking of synaptic vesicles within the presynaptic terminal are currently being intensely investigated. We and others have shown that proteins implicated in neurotransmitter release in vertebrates have been extremely well conserved during evolution. Hence, it has been relatively straightforward to isolate the Drosophila homologues of vertebrate proteins implicated in synaptic vesicle trafficking and to create mutations in the corresponding genes using a reverse genetic approach. The fruitfly, Drosophila , is an excellent model system to study this question because the awesome power of genetics combined with the availability of several functional assays, including sophisticated electrophysiological and electron microscopy paradigms, allow us to describe the defects associated with these mutations. These studies combined with FM1-43 dye-uptake experiments allow us to determine that these proteins are also involved in endocytosis. Our laboratory presently focuses on Synaptobrevin, VAP33, Hrs and Endophilin.
Most recently, we have expanded these analyses using forward mosaic genetic approaches to systematically isolate mutations in genes that play an important role in neurotransmitter release in the eye. The genes that have been identified in this screen fall into two main categories: those in which photoreceptors fail to synapse properly with the postsynaptic neurons, and those in which neurotransmitter release is impaired or abolished. Those that display subtle defects in synaptic morphology are excellent candidates for genes that play a role in synapse maturation and plasticity. Those that do not exhibit any morphological defects and lack on and off responses in electroretinograms are excellent candidates for genes that play a role in neurotransmitter release. More than 40 novel genes have now been mapped by meiotic mapping. For each, we are presently trying to clone the gene, raise antibodies against the protein, determine the subcellular localization of the protein, and define any biochemical interactions with other proteins that are localized at the synapse.
Relevance of the project to IDDRC mission:
Understanding the molecular mechanisms of neurotransmitter release will probably be very relevant to understanding the molecular pathogenesis of some forms of MR.