Novel functions of nanos in downregulating mitosis and transcription during the development of the Drosophila germline

It has previously been shown that germ cells in embryos derived from nos mu tant mothers do not migrate to the primitive gonad and prematurely express several germline-specific markers. In the studies reported here, we have tr aced these defects back to the syncytial blastoderm stage. We show that pol e cells in nos(-) embryos fail to establish/maintain transcriptional quiesc ence; the sex determination gene Sex-lethal (Sxl) and the segmentation gene s fushi tarazu and even-skipped are ectopically activated in nos- germ cell s. We show that nos- germ cells are unable to attenuate the cell cycle and instead continue dividing. Unexpectedly, removal of the Sxl gene in the zyg ote mitigates both the migration and mitotic defects of nos(-) germ cells. Supporting the conclusion that Sri is an important target for nos repressio n, ectopic, premature expression of Sxl protein in germ cells disrupts migr ation and stimulates mitotic activity.