| Research Abstract |
In this research project, steroid synthetic pathways in the ovarian follicles of the five species of marine teleost, tiger puffer, yellow tail, red seabream, Japanese mackerel, and bambooleaf wrasse, during vitellogenesis and final oocyte maturation (FOM) were investigated.
In the vitellogenic ovarian follicles in the tiger puffer, yellowtail, and Japanese mackerel, E2 is synthesized from androstendione (AD) via testosterone (T), while in red seabream and bambooleaf wrasse E2 is synthesized from AD via estrone (E1) but not T. During FOM, in all species the steroidogenic shift from estradiol-17β to 20β-hydroxylated progestin production occurred. Of the steroids produced, 17,20β-dihydroxy-4-pregnen-3-one (17,20β-P) and 17,20β,21-trihydroxy-4-pregnen-3-one (20β-S) exhibited the greatest effect on germinal vesicle breakdown (GVBD) in vitro in all species. 17,20β-dihydroxy-4-pregnen-3-one (17,20β-P) is confirmed as a maturation-inducing hormone (MIH) of the yellowtail. In the tiger puffer, it was shown that 17,20β,21-trihydroxy-4-pregnen-3-one (20β-S) was the MIH of this species. On the other hand, in the Japanese mackerel, red seabream, and bamboleaf wrasse, it has been clarified that both 17,20β-P and 20β-S play a role as MIH. Furthermore, the present study clarified the synthetic pathway of the MIH (s) in each species. In all cases, a combination of inactivation of C17, 20-lyase and activation of 20β-hydroxysteroid dehydrogenase in the ovarian follicles is the common enzymatic kinetics in the FOM.
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