Elucidating mechanisms of spermatogonial stem cell competition - Project Summary The broad, long-term objectives of this application are to characterize mechanisms that allow a competitive germline stem cell (GSC) and its descendants to dominate the GSC population and cause super-Mendelian inheritance. The proposal will determine how a GSC in the Drosophila testis remodels its niche and causes the selective loss of WT neighbor GSCs. To accomplish this, the proposal will utilize immunofluorescence, genetics, RNA interference, extended ex vivo live-cell imaging, transcriptomics, chromatin labelling, and innovative assays of GSC competition and allele inheritance in F1 offspring. We will capitalize upon the powerful genetics available in Drosophila, as well as the ability to unequivocally identify the niche, GSCs, differentiating germline cells, and somatic stem cells (CySCs) and their lineage in the Drosophila testes. This proposal is supported by our published results demonstrating that (1) loss of the transcription factor Chinmo in a GSC causes the ectopic secretion of the extracellular matrix (ECM) protein Perlecan (Pcan), (2) this Pcan accumulates around the endogenous niche resulting in an ectopic ECM termed the moat within the testis lumen; (3) the moat causes the selective loss of WT neighbor GSCs, which no longer have strong adhesion with niche cells; (4) chinmo-/- GSCs remain in the resculpted niche because they upregulate ECM-binding proteins. This proposal is also supported by our unpublished results showing that Chinmo protein expression is promoted by an RNA-binding protein (RBP) in GSCs and that a ZAD-ZNF protein likely acts as a Chinmo co-factor in GSCs. In the first goal, we will determine whether clonal loss of the RBP that promotes Chinmo expression imparts that GSC with a competitive advantage. We will also determine what regulates that RBP in GSCs and test whether loss of any regulators of the RBP imparts a competitive advantage to a mutant GSC. In the second goal, we will determine whether Chinmo and the ZAD-ZNF protein work together to repress Pcan by recruiting histone methyltransferases. We will also determine how niche cells promote the ectopic Pcan produced by chinmo-/- GSCs. In the third goal, we will test the role of somatic stem cells (CySCs) in GSC competition and assess whether they push out WT neighbors GSCs. We will also use live-cell imaging to determine the types of GSC division that occur in chinmo- /- GSCs. The studies in this proposal will increase the knowledge base about GSC competition and will foster new avenues of research into mechanisms and possible treatments for human paternal age effect disorders caused by competitive spermatogonial stem cells and for tumor cells which remodel their microenvironment to benefit themselves and disadvantage WT neighboring cells.
