A gain-of-function screen for genes controlling motor axon guidance and synaptogenesis in Drosophila

Background: The neuromuscular system of the Drosophila larva contains a sma ll number of identified motor neurons that make genetically defined synapti c connections with muscle fibers. We drove high-level expression of genes i n these motor neurons by crossing 2293 GAL4-driven EP element lines with kn own insertion site sequences to lines containing a pan-neuronal GAL4 source and UAS-green fluorescent protein elements. This allowed visualization of every synapse in the neuromuscular system in live larvae. Results: We identified 114 EPs that generate axon guidance and/or synaptoge nesis phenotypes in F1 EP x driver larvae. Analysis of genomic regions adja cent to these EPs defined 76 genes that exhibit neuromuscular gain-of-funct ion phenotypes. Forty-one of these (known genes) have published mutant alle les; the other 35 (new genes) have not yet been characterized genetically. To assess the roles of the known genes, we surveyed published data on their phenotypes and expression patterns. We also examined loss-of-function muta nts ourselves, identifying new guidance and synaptogenesis phenotypes for e ight genes. At least three quarters of the known genes are important for ne rvous system development and/orfunction in wild-type flies. Conclusions: Known genes, new genes, and a set of previously analyzed genes with phenotypes in the Adh region display similar patterns of homology to sequences in other species and have equivalent EST representations. We infe r from these results that most new genes will also have nervous system loss -of-function phenotypes. The proteins encoded by the 76 identified genes in clude GTPase regulators, vesicle trafficking proteins, kinases, and RNA bin ding proteins.