Determining how Doublesex and sex-specific steroid hormone signaling control gonad development

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PROJECT SUMMARY In the animal kingdom, sexual dimorphism, or phenotypic differences between the sexes, is seen in most species. In Drosophila, the key factor controlling sexual dimorphism is Doublesex (Dsx), the founding member of the conserved Doublesex/Mab-3 Related Transcription Factor (DMRT) family. DMRTs have central roles in sex determination across many species including flies, humans, and mice. Although few Dsx targets have been characterized, our lab has shown that Dsx regulates sex-specific steroid hormone Ecdysone (E) signaling through female-specific Ecdysone Receptor (EcR) expression, and that this functions to promote ovary development and repress testis development at a key developmental timepoint. Bioinformatic analyses has been used to predict Dsx targets, and many of these are transcription factors that contain a Broad-complex, tramtrack, and bric-a-brac (BTB) domain, a protein-protein interaction motif. To identify Dsx targets that play a role in sexual dimorphism of the gonad, I performed a reverse screen of BTB domain proteins containing putative Dsx binding motifs using RNA interference. As a result, I found that loss of mamo in somatic cells of the gonad led to severely disorganized ovaries and, in some cases, the formation of rudimentary testes in XX animals. Given these findings, I hypothesize that mamo is critical for proper development in the Drosophila ovary, and that it functions downstream of Dsx and E signaling to help establish a female sexual fate. This hypothesis will be addressed by first examining the cell-type-specific expression of Mamo throughout development and performing genetic interaction assays with dsx. I will characterize what cell types are affected in the absence of mamo using cell-specific markers and ascertain whether loss of mamo results in sex transformation properties of the ovary. A second BTB domain protein, Chinmo, has been shown to be important in the testis, and the relationship between mamo and chinmo, and how E signaling regulates these factors, will be determined. This work will expand current knowledge on how DMRTs control sexual dimorphism and could uncover genes critical for sexual identity in both flies and mammals. Due to the universal nature of DMRTs in controlling sex-specific development, understanding their targets and how they function is of great importance for reproductive health and has the potential to broaden our knowledge of human infertility.