THE SOMATIC SEX DETERMINES THE REQUIREMENT FOR OVARIAN TUMOR GENE ACTIVITY IN THE PROLIFERATION OF THE DROSOPHILA GERMLINE

Gametogenesis in Drosophila requires sex-specific interactions between the soma and germline to control germ cell viability, proliferation, and differentiation. To determine what genetic components are involved in this interaction, we examined whether changes in the sexual identi ty of the soma affected the function of the ovarian tumor (otu) and ov o genes. These genes are required cell autonomously in the female germ line for germ cell proliferation and differentiation. Mutations in otu and ovo cause a range of ovarian defects, including agametic ovaries and tumorous egg cysts, but do not affect spermatogenesis. We demonstr ate that XY germ cells do not require otu when developing in testes, b ut become dependent on otu function for proliferation when placed in a n ovary. This soma-induced requirement can be satisfied by the induced expression of the 98x10(3) M(r) OTU product, one of two isoforms prod uced by differential RNA splicing. These results indicate that the fem ale somatic gonad can induce XY germ cells to become 'female-like' bec ause they require an oogenesis-specific gene. In contrast, the require ment for ovo is dependent on a cell autonomous signal derived from the X:A ratio. We propose that differential regulation of the otu and ovo genes provides a mechanism for the female germline to incorporate bot h somatic and cell autonomous inputs required for oogenesis.