Mitochondria in post-meiotic early round Drosophila spermatids aggregate and fuse into the Nebenkern, which consists of two interwoven large mitochondrial derivatives that together form a spherical structure equal in size to the nucleus. Homozygous knon males are sterile, showing defective internal Nebenkern structure and subsequent faulty elongation of mitochondrial derivatives along the growing spermatid axoneme. knon encodes a testis-specific isoform of an ATP synthase subunit that, based on its size and structure, may alter ATP synthase dimerization, a phenomenon known to mediate cristae morphology in many systems. We hypothesize that tissue-specific ATP synthase dimerization dynamics may underlie the unusual mitochondrial shaping within the Nebenkern. To test the role of Knon in mitochondrial dynamics and ATP synthase dimerization, we exogenously expressed it in flight muscle and larval brain using the GAL4-UAS system; we assessed mitochondrial structure via fluorescence microscopy, and ATP synthase dimerization via immunoblots of blue native gels. While preliminary data in flight muscle show no large scale alteration of mitochondrial shape, Knon exogenous expression did shift the balance of ATP synthase dimers and monomers, though less than when peripheral stalk components are knocked down via RNAi. Knon expression in flight muscle with simultaneous knockdown of the paralogous broadly-expressed subunit does not restore wild type ATP synthase complex formation as detected by BN PAGE, suggesting that Knon cannot substitute for its paralog in this tissue. Further studies of knon and other testis-specific ATP synthase subunit paralogs may help elucidate the basis for unusual mitochondrial dynamics in the Nebenkern.