Functional Spliceosome Associated Protein 121 (fSAP121)

Virilizer (vir) is required in somatic cells for the female-specific splicing of Sxl primary transcripts and for an unknown vital process in both sexes. In the soma, clones of XX cells lacking Sxl or vir are sexually transformed and form male structures; in the germline, XX cells mutant for Sxl extensively proliferate, but are unable to differentiate. XX germ cells mutant for vir, in contrast to cells mutant for Sxl, perform oogenesis. The early production of SXL in undifferentiated germ cells is independent of vir while, later in oogenesis, expression of Sxl becomes dependent on vir. However, vir must be active in the female germline to allow normal embryonic development because maternal products of vir are required for the early post-transcriptional regulation of Sxl in XX embryos and for a vital process in embryos of both sexes.