Gonadal functions and their hormonal controls in hagfish

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To clarify the gonadal functions of most primitive vertebrates, hagfish, we measured plasma concentrations of sex steroid, estradiol, with respect to gonadal development. In both sexes, plasma E2 showed a significant correlation with gonadal development, suggesting that estradiol is involved in the regulation of functional differentiation of gonads. We also isolated the cDNA sequence encoding cholesterol side-chain cleavage enzyme (CYP11A), which involves in the first reaction in the process of steroidogenesis. The enzyme was localized on the Leydig cells and follicle cells in testis and ovary, respectively. The CYP11A transcripts increased significantly in accordance with the developmental condition of gonads. Our findings suggest hagfish might possess similar process of sex steroidogenesis, as proposed in jawed vertebrates.