RNA-Seq Analysis Unraveled Genes and Pathways Involved in Testicular Differentiation in Channel Catfish

Channel catfish (Ictalurus punctatus) is the primary aquaculture species in the US. It’s also a great model for studying sex differentiation and determination because of its sexual plasticity. It’s known that male sexual organ differentiation occurs between the 90 and 110 day post-fertilization (dpf). In this work, we conducted Illumina-based RNA-Seq of the male and female gonad at 90 dpf, 100 dpf and 110 dpf to profile gene expression dynamics during gonadal development. The differential gene expression analysis showed that 1,518, 1,544 and 1,070 genes were highly expressed in male gonad at 90 dpf, 100 dpf and 110 dpf, respectively. Using 90 dpf as control, we identified 29 and 264 genes that were up-regulated at 100 dpf and 110 dpf in the male gonad, respectively. In contrast, 37 and 259 genes were found to be suppressed at 100 dpf and 110 dpf in the male gonad, respectively. Further examination allowed identification of a number of genes with known functions in gonadal development, including Sox11b and Dmrt2b that were overexpressed in female gonad, while Gsdf and FoxI3 transcription factors that were overexpressed in male gonad. Pathway analysis suggested that several important pathways were involved in the progression of gonad development including pathways related to ovarian steroidogenesis and hormone signaling, androgen receptor signaling pathway and cytoskeleton remodeling pathway which mediated ectoplasmic specialization and seminiferous duct organization. This study laid the foundation for further sex studies and should be valuable in facilitating the production of monosex population for catfish aquaculture.