Roles of two cyp11 genes in sex hormone biosynthesis in Japanese flounder (Paralichthys olivaceus)

The P450 side-chain cleavage enzymes P450scc (Cyp11a) and 11β-hydroxylase (Cyp11b) play important roles in sex steroid and cortisol production. Here, two duplicates of cyp11 genes were identified in Japanese flounder (Paralichthys olivaceus): Pocyp11a and Pocyp11b, respectively. Phylogenetic analysis and amino acid sequence alignment revealed that Pocyp11a and Pocyp11b shared significant identity with sequences of other teleost fish species. The quantitative real-time polymerase chain reaction (qRT-PCR) results indicated that among the studied tissues, brain tissue showed the highest expression of Pocyp11a, followed by kidney and testis tissues, whereas Pocyp11b expression was highest in the testis. The expression patterns of these two genes showed sexual dimorphism, with both genes showing higher expression in the testis than in the ovary. In-situ hybridization analysis demonstrated that Pocyp11a and Pocyp11b mRNA were both detected in oocytes, spermatocytes, and Sertoli cells, indicating that they might be involved in hormone synthesis. The expression levels of Pocyp11a and Pocyp11b were significantly downregulated by treatment with 17α-methyltestosterone (17α-MT) in the testis and ovary in both in vivo and studies. In vivo studies showed that Pocyp11a and Pocyp11b transcripts were suppressed by 17β-estradiol (E2 ) treatment in both the testis and ovary. In addition, in vitro studies showed that the expression level of Pocyp11b was decreased by treatment with E2 , whereas that of Pocyp11a was largely unaffected. Moreover, the expression levels of Pocyp11a and Pocyp11b in the testis cell line were significantly upregulated after NR0b1 and NR5a2 (p < .05) treatment. These results indicate that Pocyp11a and Pocyp11b might play important roles in sex hormone biosynthesis. Our research can assist future studies of the mechanisms of steroid biosynthesis and functional differences between cyp11a and cyp11b in Japanese flounder.