CG9723 is required for spermatogenesis in Drosophila. Robyn Rosenfeld^1,2, Helen McNeill^1,2. 1) Samuel Lunenfeld Research Institute, Mount Sinai hospital, Toronto, ON, Canada; 2) Molecuar Genetics, University of Toronto, Toronto, ON, Canada.

   In Drosophila, testes development is a complex process regulated by the interplay between germline stem cells and somatic stem cells. Through a screen to identifying regulators of growth, we found a novel gene, CG9723, that is essential for proper testes development. CG9723 was previously uncharacterized and encodes a multi-pass transmembrane protein of 450 amino acids with a highly conserved domain of unknown function (DUF2215). Antibody analysis indicates that CG9723 is a nuclear membrane protein, with high expression in the apical tip of the testes that declines basally. We generated a CG9723 null allele through ends-out gene targeting and found that homozygous mutant flies display male sterility and lethality phenotypes. Flies lacking CG9723 have small testes that lack proper cyst structure and rarely produce late stage sperm cells. The hub of the testis, the niche for the stem cells, and stem cells directly surrounding the hub appear normal. However, after this stage, the organization and morphology of the cells are abnormal. The testis contains both somatic and germ cells. By expressing CG9723 within different compartments of CG9723 null flies, we determined that CG9723 is required in the somatic cells of the testis. Interestingly, there are significantly more early somatic cells in CG9723 null males compared to wild type. The nuclear membrane structure in mutant flies is relatively normal, suggesting that CG9723 is essential for proper signalling. Interestingly, CG9723 homologues are highly expressed in mammalian spermatogenesis, suggesting that CG9723 may play a conserved role in sperm development.