The Comparative Survey of Coordinated Regulation of Steroidogenic Pathway in Japanese Flounder () and Chinese Tongue Sole ().

Steroidogenesis controls the conversion of cholesterol into steroid hormones through the complex cascade reaction of various enzymes, which play essential roles in sexual differentiation and gonadal development in vertebrates, including teleosts. Japanese flounder () and Chinese tongue sole () are important marine cultured fishes in China and have remarkable sexual dimorphism with bigger females and sex reversal scenarios from female to neo-male. Several steroidogenic genes have been analyzed individually in the two species, but there is a lack of information on the coordinated interaction of steroidogenic gene regulation. Therefore, in this study, through genomic and transcriptomic analysis, 39 and 42 steroidogenic genes were systematically characterized in and genomes, respectively. Phylogenetic and synteny analysis suggested a teleost specific genome duplication origin for /, /, / and / but not for / and /. Comparative transcriptome analysis revealed conserved expression patterns for steroidogenic genes in and gonads; /, /, /, , , and were strongly expressed in testis, while and genes were highly expressed in ovaries. Only a few genes were differentially expressed between male and neo-male testis of both and , and even fewer genes were differentially regulated in the brains of both species. Network analysis indicated that , and actively interacted with other steroidogenic genes in and , and may play a more sophisticated role in the steroid hormone biosynthesis cascade. The coordinated interaction of steroidogenic genes provided comprehensive insights into steroidogenic pathway regulation with a global biological impact, as well as sexual development in teleost species.