INVESTIGATING THE MOLECULAR CONTROL OF ECDYSONE RESPONSE GENE, E74, IN THE DROSOPHILA OVARY.

Oogenesis is the process by which an egg develops from precursor cells in the ovary. This process has been widely studied\; however, many of the molecular mechanisms that regulate oocyte development and growth remain unclear. The Drosophila melanogaster ovary is an exceptional model system for studying the mechanisms of oogenesis. As in humans, germ cells are surrounded by somatic cells which aid proper oocyte development and maturation. Steroid hormones largely drive this process, and in Drosophila, the predominant steroid hormone is ecdysone, similar to human estrogen. Ecdysone binds to a heterodimeric receptor which then functions as a transcription factor to promote gene expression. Other factors, including additional transcription factors and chromatin remodeling factors, likely refine this response. Ecdysone signaling is necessary for oogenesis via the regulation of many target genes. One target, Ecdysone-induced protein at 74EF (E74), is required for oogenesis and is highly expressed in ovarian germ cells\; however, regulation of E74 expression in the ovary has not been well-studied. To investigate how E74 expression is regulated in the ovary, we used enhancer mapping to identify regions of the E74 locus critical for germline expression. Twenty-eight fly lines carrying pieces of the E74 gene locus fused to a minimal promoter and Gal4 were crossed with flies containing UAS-lacZ responder transgene. We identified two 200-bp regions within a large intron of the E74 locus that are sufficient to drive expression of a reporter. Together, these regions fully recapitulate the endogenous E74 expression pattern. We then identified several factors, including the chromatin binding factor Trl, as putative regulators of E74 expression at those sites. Trl expression partially overlaps with that of E74, suggesting that Trl may be an important modifier of ecdysone signaling in oogenesis. Future studies will characterize the roles of Trl in this process