Roles for testis-enriched ATP synthase subunits in mitochondrial shaping during Drosophila spermatogenesis. Eric M. Sawyer, Olivia Brown, Yihharn Hwang, Lauren Ivey, Kelsey E. Sheaffer, Conroy Field, Taylor Gunnell, Karen G. Hales. Department of Biology, Davidson College, Davidson, NC.

   After meiosis in wild type Drosophila spermatids, mitochondria aggregate near the nucleus, and their membranes rearrange to form two large mitochondrial derivatives folded into a structure called the Nebenkern. During sperm tail elongation, the two derivatives unfurl and lengthen, and one derivative ultimately remains to power the sperm flagellum. Males homozygous for the ms(2)1400 mutation exhibit mitochondrial clumping during the elongation stage of spermatogenesis, leading to male sterility. A lack of mitochondrial fusion bypasses the mitochondrial elongation defect, demonstrating that ms(2)1400 does not directly cause elongation failure but instead a defect in internal Nebenkern structure. CG7813, encoding a testis-enriched paralog of the d-subunit of ATP synthase with an additional protein domain, is the gene associated with the ms(2)1400 phenotype. In addition to its paradigmatic catalytic role, ATP synthase also plays an important role in cristae shaping, a property that has been described in other models, particularly yeast. In prior research, CG7813 was investigated using RNAi knockdown via the GAL4-UAS system. The resulting phenotypes resembled the clumping during elongation found in the ms(2)1400 mutants. To further understand the function of CG7813, current efforts are focused on constructing a transgene for rescue experiments and GFP-tagged transgenes to visualize protein localization in developing spermatids. To explore the role of additional ATP synthase subunits in mitochondrial dynamics, we knocked down expression in the testis of subunits g, F6, b, and in the testis using RNAi. Results demonstrated a variety of mutant phenotypes primarily involving Nebenkern structure, such as vacuolated Nebenkerne, abnormal mitochondrial shaping, and ultimately non-motile sperm tails. The results serve as a further indication of the important role of ATP synthase in mitochondrial morphology.