PUNT AND SCHNURRI REGULATE A SOMATICALLY DERIVED SIGNAL THAT RESTRICTS PROLIFERATION OF COMMITTED PROGENITORS IN THE GERMLINE

To identify regulators of stem cell lineages, we are focusing on sperm atogenesis in Drosophila. In spermatogenesis, each germline stem cell divides asymmetrically, renewing itself and producing a transiently am plifying daughter, which divides four times, By screening for mutants in which daughter cells fail to stop dividing, we find that the TGF-be ta signal transducers schnurri and punt are required to limit transien t amplification of germ cells, Mosaic analysis demonstrates that punt and schnurri act within somatic cyst cells that surround germ cells, r ather than in germ cells, Thus, a cyst-cell-derived signal restricts g erm cell proliferation and this signal is initiated by input from a me mber of the TGF-beta superfamily, Thus, a signal relay regulates progr ession through the germline stem cell lineage.