Elucidating the role of the nuclear hormone receptor E78 in Drosophila oogenesis. Elizabeth T. Ables^1,2, Kelly E. Bois², Daniela Drummond-Barbosa². 1) Dept. of Biology, East Carolina University, Greenville, NC; 2) Dept. of Biochemistry and Molecular Biology, Johns Hopkins University School of Public Health, Baltimore, MD.

   Nuclear hormone receptors (NHRs) have emerged as important regulators of mammalian and Drosophila adult physiology, affecting such seemingly diverse processes as adipogenesis, carbohydrate metabolism, circadian rhythm, stem cell function, and gamete production. Indeed, the steroid hormone ecdysone, and its cognate NHRs EcR and Usp, have multiple roles in Drosophila development and regulate key processes during oogenesis, including germline stem cell (GSC) function and follicle development. Other NHRs, including Hr39 and E75, also have known roles in the Drosophila female reproductive system; however, the function of most NHRs in oogenesis remains largely undescribed. Because of its similarity to mammalian PPARs and Rev-Erb, which are central to the control of metabolism and circadian rhythm, the NHR E78 is a particularly attractive candidate that may link oogenesis with the physiological status of the organism. In support of a role during oogenesis, we find that E78 appears to be weakly expressed in germ cells, and enriched in somatic border cells and late-stage follicle cells. We generated a predicted molecular null allele, E78³¹, and find that despite previous reports that hypomorphic E78 mutants have no obvious fertility defects, homozygous viable E78³¹ females are sub-fertile. Decreased egg production is likely due to a combination of factors, including decreased GSC number and a partial block to vitellogenesis. We are currently investigating the mechanisms by which E78 regulates oogenesis. Taken together with the known roles of EcR, Usp, E75, and Hr39, our results suggest that NHRs may be critical for the broad transcriptional control of a wide variety of cellular processes during oogenesis.