Ovarian tumor expression is dependent on the functions of the somatic sex regulatory genes transformer-2 and doublesex.

The doublesex-dependent sex regulatory pathway in Drosophila controls major aspects of somatic sexual differentiation, but its expression is not required in the X/X germline. Nevertheless, mutations in doublesex and in the genes that directly regulate its expression, transformer and transformer-2, disrupt early stages of oogenic differentiation to produce gonads containing immature germ cells. This indicates a critical, but uncharacterized, set of soma-germline interactions essential for oogenesis. In this paper, we examined the effects of mutations in transformer-2 on the expression and function of the germline-specific ovarian tumor gene. We demonstrated that in transformer-2 mutants, there was a marked reduction in the activity of the ovarian tumor promoter in the mutant germline. In addition, the phenotypic effects on the arrested germline could be partially suppressed by the simultaneous over-expression of both ovarian tumor and a second germline gene, Sex-lethal. This differs from transformer mutations, in which the over-expression of ovarian tumor alone is sufficient for a similar improvement in germline differentiation. In contrast to transformer-2, doublesex activity was not required for ovarian tumor promoter activity and we found indirect evidence that the doublesex male-specific function might have a negative regulatory effect. These data indicate that the components of the genetic pathway regulating somatic sexual differentiation have specific and differential effects on germline gene activity.