Identification of genes affecting glutamate receptor expression at the Drosophila neuromuscular junction

The formation of glutamatergic synapses is essential for a number of important neurobiological processes. The identification of proteins required for synapse formation and glutamate receptor expression and localization is critical to better understand these processes. Using forward genetics, I have identified several genes that may be involved in the differentiation of the glutamatergic synapse and the formation of glutamate receptor clusters in Drosophila melanogaster. My results, in agreement with previous studies, suggest that genes encoding several types of proteins are responsible for proper formation and development of glutamatergic synapses, including ATP- and GTPases, cytoskeletal regulators, cell adhesion molecules, kinases, phosphatases, RNA regulators, regulators of protein formation, transcription factors, and transporters. Twenty one per cent of the identified genes that disrupt glutamatergic synaptogenesis are in genes encoding proteins of novel or unknown function.; One candidate gene, sec8, which was characterized by abnormal synaptic morphology and an underexpression of glutamate receptors, was chosen for further study. Sec8 is enriched at glutamatergic neuromuscular junctions (NMJs). In sec8 mutant NMJs, postsynaptic glutamate receptors are distributed diffusely throughout the cell rather than localized properly. Other synaptic proteins (synaptotagmin, CSP, DLG) appear normal. Previous studies showed that recombinant sec proteins inhibit tubulin polymerization. Drosophila sec8 mutants show increased synaptic microtubule immunoreactivity at NMJs. Genetically increasing tubulin directly causes glutamate receptor loss. I propose that transport vesicles carrying glutamate receptors are deposited at synapses due to local termination of the microtubule network by synaptic Sec8 complexes.