Ecdysone response genes govern egg chamber development during mid-oogenesis in Drosophila

The steroid hormone ecdysone regulates larval development and metamorphosis in Drosophila melanogaster through a complex genetic hierarchy that begins with a small set of early response genes. Here, we present data indicating that the ecdysone response hierarchy also mediates egg chamber maturation during mid-oogenesis. E75, E74 and BR-C are expressed in a stage-specific m anner while EcR expression is ubiquitous throughout oogenesis. Decreasing o r increasing the ovarian ecdysone titer using a temperature-sensitive mutat ion or exogenous ecdysone results in corresponding changes in early gene ex pression. The stage 10 follicle cell expression of E75 in wild-type, K10 an d EGF receptor (Egfr) mutant egg chambers reveals regulation of E75 by both the Egfr and ecdysone signaling pathways. Genetic analysis indicates a ger mline requirement for ecdysone-responsive gene expression, Germline clones of E75 mutations arrest and degenerate during mid-oogenesis and EcR germlin e clones exhibit a similar phenotype, demonstrating a functional requiremen t for ecdysone responsiveness during the vitellogenic phase of oogenesis. F inally, the expression of Drosophila Adrenodoxin Reductase increases during mid-oogenesis and clonal analysis confirms that this steroidogenic enzyme is required in the germline for egg chamber development, Together these dat a suggest that the temporal expression profile of E75, E74 and BR-C may be a functional reflection of ecdysone levels and that ecdysone provides tempo ral signals regulating the progression of oogenesis and proper specificatio n of dorsal follicle cell fates.