Identification of cytoskeletal genes that are essential for lifelong maintenance of muscle function. Guy Tanentzapf, Alexander D. Perkins, Michael Lee, Fayeza Islam. CPS Dept, Univ British Columbia, Vancouver, BC, Canada.

   In the adult animal, muscles maintain their function while bearing substantial mechanical loads and undergoing numerous contraction/extension cycles. How muscles are able to maintain function for long periods of time is presently not well understood. Drosophila melanogaster provides an attractive system in which to study the genetics of muscle tissue maintenance. The basic unit of muscle is the sarcomere which is primarily composed of cytoskeletal proteins. We therefore hypothesised that cytoskeletal proteins are required to maintain muscle function in the adult fly. A recently developed gene expression system, TARGET, has made it possible to limit gene expression to adults. We used the TARGET system to carry out a systematic RNAi-meditated knockdown screen of cytoskeletal genes in the adult fly. We used robust and sensitive behavioural assays to perform high-time resolution analysis of fly muscle function. This approach identified 48 genes that caused a significant decline in adult muscle function and of these, 40 had not been previously implicated in muscle maintenance. Detailed analysis of candidate genes using confocal and electron microscopy showed that while muscle architecture was largely maintained after gene knockdown, defects in sarcomere length were observed suggesting that that these genes are required to maintain tension in sarcomere. Consistent with this hypothesis we used pulse-chase experiments to show that some of the candidate hits we identified undergo turnover in sarcomeres at the Z-disc. Together, our results provide direct evidence of in vivo muscle protein turnover, identify new candidate genes required for muscle tissue maintenance, and identify specific functional defects associated with knockdown of key sarcomeric components in the adult animal.