The daughterless gene functions together with Notch and Delta in the control of ovarian follicle development in Drosophila

The daughterless (da) gene in Drosophila encodes a broadly expressed transcriptional regulator whose specific functions in the control of sex determination and neurogenesis have been extensively examined. We describe here a third major developmental role for this regulatory gene: follicle formation during oogenesis. A survey of da RNA and protein distribution during oogenesis reveals a multiphasic expression pattern that includes both germline and soma. Whereas the germline expression reflects da's role in progeny sex determination, the somatic ovary expression of da correlates with the gene's role during egg chamber morphogenesis. Severe, but viable, hypomorphic da mutant genotypes exhibit dramatic defects during oogenesis, including aberrantly defined follicles and loss of interfollicular stalks. The follicular defects observed in da mutant ovaries are qualitatively very similar to those described in Notch (N) or Delta (Dl) mutant ovaries. Moreover, in the ovary da- alleles exhibit dominant synergistic interactions with N or Dl mutations. We propose that all three of these genes function in the same regulatory pathway to control follicle formation.