VIRILIZER REGULATES SEX-LETHAL IN THE GERMLINE OF DROSOPHILA-MELANOGASTER

In Drosophila, the gene Sex-lethal (Sxl) is required for female develo pment. It controls sexual differentiation in the soma, dosage compensa tion and oogenesis. The continuous production of SXL proteins in XX an imals is maintained by autoregulation and depends on virilizer (vir). This gene is required in somatic cells for the female-specific splicin g of Sri primary transcripts and for an unknown vital process in both sexes. In the soma, clones of XX cells lacking Sri or vir are sexually transformed and form male structures; in the germline, XX cells mutan t for Sri extensively proliferate, but are unable to differentiate. We now studied the role of vii in the germline by generating germline ch imeras. We found that XX germ cells mutant for vir, in contrast to cel ls mutant for Sri, perform oogenesis, We show that the early productio n of SXL in undifferentiated germ cells is independent of vir while, l ater in oogenesis, expression of Sri becomes dependent on vir, We conc lude that the early SXL proteins are sufficient for the production of eggs whereas the later SXL proteins are dispensable for this process. However, vir must be active in the female germline to allow normal emb ryonic development because maternal products of vir are required for t he early posttranscriptional regulation of Sri in XX embryos and for a vital process in embryos of both sexes.