Diverse somatic Transformer and sex chromosome karyotype pathways regulate gene expression in Drosophila gonad development

The somatic sex determination genetransformer(tra) is required for the highly sexually dimorphic development of most somatic cells, including those of the gonads. In addition, somatictrais required for the germline development even though it is not required for sex determination within germ cells. Germ cell autonomous gene expression is also necessary for their sex determination. To understand the interplay between these signals, we compared the phenotype and gene expression of larval wild-type gonads and the sex-transformedtragonads. XX larval ovaries transformed into testes were dramatically smaller than wild-type, with significant reductions in germ cell number, likely due to altered geometry of the stem cell niche. Additionally, there was a defect in progression into spermatocyte stages. XY larval testes transformed into ovaries had excessive germ cells, possibly due to the earlier onset of cell division. We suggest that germ cells are neither fully female nor male following somatic sex transformation, with certain pathways characteristic of each sex expressed intramutants. We found multiple patterns of somatic and germline gene expression control exclusively due totra, exclusively due to sex chromosome karyotype, but usually due to a combination of these factors showingtraand sex chromosome karyotype pathways regulate gene expression during Drosophila gonad development.