BAG-OF-MARBLES AND BENIGN GONIAL CELL NEOPLASM ACT IN THE GERMLINE TORESTRICT PROLIFERATION DURING DROSOPHILA SPERMATOGENESIS

Stem cells divide asymmetrically, regenerating a parental stem cell an d giving rise to a daughter cell with a distinct fate, In many stem ce ll lineages, this daughter cell undergoes several amplificatory mitose s, thus generating more cells that embark on the differentiation progr am specific for the given lineage, Spermatogenesis in Drosophila is a model system to identify molecules regulating stem cell lineages, Muta tions at two previously identified loci, bag-of-marbles (barn) and ben ign genial cell neoplasm (bgcn), prevent progression through spermatog enesis and oogenesis, resulting in the overproliferation of undifferen tiated germ cells, Here we investigate how bam and bgcn regulate the m ale germline stem cell lineage, By generating FLP-mediated clones, we demonstrate that both bam and bgcn act autonomously in the germline to restrict proliferation during spermatogenesis, By using enhancer trap lines, we find that the overproliferating germ cells express markers specific to amplifying germ cells, while at the same time retaining th e expression of some markers of stem cell and primary spermatogonial c ell fate, However, we find that germ cells accumulating in bam or bgcn mutant testes most resemble amplifying germ cells, because they under go incomplete cytokinesis and progress through the cell cycle in synch rony within a cyst, which are two characteristics of amplifying germ c ells, but not of stem cells, Taken together, our results suggest that bam and bgcn regulate progression through the male germline stem cell lineage by cell-intrinsically restricting the proliferation of amplify ing germ cells.