Studies on the regulation of aromatase activity in mature female ice goby

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Ice goby, Leucopserion petersi, is a small anadromous fish. Females enter the river with yolk-accumulating ovaries, then, vitellogenesis once stops in the river, and the ovaries rapidly develop in the nest before spawning. To clarify the endocrinological mechanisms of this discontinuation of yolk accumulation, effects of gonadotropins (GTHs) on estradiol-17β (E_2) production were investigated in vitro, using the ovaries of females captured in the river. Of GTHs tested, salmon pituitary extract (SPE) was effective in E_2 production at higher doses (1-10μg/mL). Human chorionic gonadotropin and pregnant mares' serum gonadotropin also showed a significant effect (1-10 IU/mL). Actinomycin D and cycloheximide significantly inhibited E_2 production stimulated by SPE. In the absence of GTHs ovary fragments produced only a marginal amout of E_2. These results indicate that the resting ovaries from the fish captured just after entering the river have rather low aromatase (P450 arom) activity, but it is evoked by the administrations of GTHs. For further studies, P450 arom cDNA was cloned from the developing ovaries. The cDNA encoding ice goby P450 arom (A type) was 1997bp in length and encoded a putative protein of 517 amino acids. The level of A type P450 arom mRNA expression was low in the river but rapidly increased in the nest. From the head containing the brain, another type of P450 arom cDNA was cloned (possibly B type). The deduced amino acid sequence of the A type P450 arom shared about 60% homology with that of B type.