Drosophila Cyclin J And The Somatic Pirna Pathway Cooperate To Regulate Germline Stem Cells

Cyclin J (CycJ) is a highly conserved cyclin that is uniquely expressed specifically in ovaries in Drosophila. Deletion of the genomic region containing CycJ and adjacent genes resulted in a genetic interaction with neighboring piRNA pathway gene, armitage (armi). Here I assessed oogenesis in CycJ null in the presence or absence of mutations in armi or other piRNA pathway genes. Although CycJ null flies had decreased egg laying and hatching rates, ovaries appeared normal indicating that CycJ is dispensable for oogenesis under normal conditions. Further double mutant analysis of CycJ and neighbor armi, as well as two other piRNA pathway members (piwi and aub), revealed that CycJ genetically interacts with the piRNA pathways by enhancing their ability to regulate oogenesis. Double mutants of CycJ and mutants of piwi or armi produced mispackaged egg chambers containing an overabundance of germline cells, while double mutants of CycJ and piwi or armi had more severe defects. CycJ mutants also genetically interacted with mutants of the germline piRNA pathway member aub, resulting in unique oogenesis defects, though they were less severe than defects in double mutants of CycJ and piwi or armi. Piwi and Armi are known to function in both the germline and germline-associated somatic cells. Here I show that the somatic function of armi and piwi promote egg chamber packaging in part by limiting BMP signaling and the accumulation of excess germline stem cells (GSCs) and that CycJ appears to cooperate with the somatic piRNA pathway. The increase of GSCs in armi, piwi, or CycJ double mutants depends on increased BMP signaling. Finally, CycJ promotes follicle cell proliferation in the absence of armi. My results suggest that CycJ genetically interacts with the somatic piRNA pathway to promote egg chamber packaging, limit BMP signaling, limit GSC accumulation, and promote proliferation of follicle cells