The effect of altered mitochondrial function on larval development and adult lifespan. Rachel T. Cox, Aditya Sen. Dept Biochemistry and Molecular Bio, Uniformed Services University, Bethesda, MD.

   Mitochondria are highly dynamic organelles that are responsible for making ATP. The structural and functional integrity of mitochondria are vital for proper cellular function. During development, different tissues at different stages vary in their need for mitochondrial output. In order to understand how mitochondrial requirements and dynamics change during development, we are characterizing the gene clueless (clu). Homologs for clu are found in all eukaryotes for which there is genomic sequence available. clu mutant adults are small, highly uncoordinated and have greatly reduced lifespans. Part of the coordination deficits are caused by defects in muscle mitochondria, however we have found Clu is highly expressed in larval neuroblasts and other regions of the dividing larval brain. Mitochondria in clu mutant neuroblasts are mislocalized during the cell cycle, but overall brain morphology appears to be normal. Mutations in two other genes important for mitochondrial function, technical knockout and stress sensitive B, do not mislocalize neuroblast mitochondria, suggesting this defect in mitochondrial dynamics is clu specific. Even though there are high levels of Clu expression in the brain, and very few clu mutant adults in any given culture, Clu does not appear to be required for overall larval development. In uncrowded conditions, larval development and pupation are only slightly delayed. However, only 40% of the flies are able to eclose, and clu mutant adults die after only three days. In addition, ATP levels are normal in clu mutant larvae and they do not suffer mitochondrial oxidative damage. In contrast, when the flies eclose, ATP levels plummet and mitochondria accumulate oxidative damage. These results support that Clu functions upstream of electron transport and oxidative phosphorylation and helps to suppress mitochondrial oxidative damage in the cell. In addition, these results support previous work indicating larvae do not use their mitochondria for oxidative phosphorylation, but rather rely on aerobic glycolysis for ATP (Tennessen et al, 2011).