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 t ranscriptional regulator whose specific functions in the control of se x determination and neurogenesis have been extensively examined. We de scribe here a third major developmental role for this regulatory gene: follicle formation during oogenesis. A survey of da RNA and protein d istribution 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 exp ression of da correlates with the gene's role during egg chamber morph ogenesis. Severe, but viable, hypomorphic da mutant genotypes exhibit dramatic defects during oogenesis, including aberrantly defined follic les and loss of interfollicular stalks. The follicular defects observe d in da mutant ovaries are qualitatively very similar to those describ ed in Notch (N) or Delta (Dl) mutant ovaries. Moreover, in the ovary d a(-) alleles exhibit dominant synergistic interactions with N or Dl mu tations. We propose that all three of these genes function in the same regulatory pathway to control follicle formation.