Regulation of 17α-Hydroxyprogesterone Production during Induced Oocyte Maturation and Ovulation in Amur Sturgeon (Acipenser schrenckii)

In several teleosts, 17 alpha, 20 beta-dihydroxy-4-pregnen-3-one (DHP) has been identified as a maturation-inducing steroid. DHP is synthesized from 17 alpha-hydroxyprogesterone (17OHP) by 17 beta-hydroxysteroid dehydrogenase type 12-like (hsd17b12L). Along with 3 beta-hydroxysteroid dehydrogenase/& UDelta;5-4 isomerase (3 beta-HSD), 17 alpha-hydroxylase and C17-20 lyase are associated with 17OHP production. This study aimed to determine the roles of Amur sturgeon hsd3b, P450c17-I (cyp17a1), and P450c17-II (cyp17a2) in 17OHP production and to examine their enzyme activity and mRNA expression pattern during oocyte maturation. In the sturgeons used in this study, hsd3b encoded 3 beta-HSD, cyp17a1 catalyzed 17 alpha-hydroxylase production with C17-20 lyase activity, and cyp17a2 processed 17 alpha-hydroxylase activity alone. In the ovarian follicles of individuals that underwent induced ovulation, hsd3b mRNA levels increased rapidly, cyp17a1 expression was downregulated, and cyp17a2 expression was upregulated during oocyte maturation. Finally, an in vitro study revealed that salmon pituitary extract (SPE) stimulation rapidly induced hsd3b expression, whereas cyp17a1 expression was downregulated. In vitro, cyp17a2 expression did not rapidly increase with SPE stimulation. This rapid upregulation of hsd3b during oocyte maturation was first observed in teleosts. It was suggested that hsd17b12L expression is upregulated after 17OHP production, which is regulated by hsd3b, cyp17a1, and cyp17a2, resulting in DHP production.