Aromatase inhibitor and 17 alpha-methyltestosterone cause sex-reversal from genetical females to phenotypic males and suppression of P450 aromatase gene expression in Japanese flounder (Paralichthys olivaceus)

The sex of Japanese flounder (Paralichthys olivaceus) is easily altered by water temperature or sex steroid hormone treatment during the period of sex determination. We have previously shown that rearing the genetically femal e larvae at high water temperature caused the suppression of P450 aromatase (P450arom) gene expression in the gonad and phenotypic sex-reversal of the individuals to males (Kitano et al. 1999. J Mol Endocrinol 23:167-176). In the present study, we show that treatment of genetically female larvae wit h fadrozole (aromatase inhibitor) or 17 alpha-methyltestosterone induces se x-reversal as well as suppression of P450arom gene expression. The effect o f fadrozole was counteracted by co-administration of estradiol-17 beta. Eff ective periods for fadrozole treatment to induce sex-reversal were similar to those for high water temperature treatment. RT-PCR did not detect P450ar om mRNA in gonad of the sex-reversed, phenotypic males. These results indic ate that sex-reversal of the genetically female larvae by aromatase inhibit or (or 17 alpha-methyltestosterone) may be due to the suppression of P450ar om gene expression and the resultant decrease in the amount of estrogen. (C ) 2000 Wiley-Liss, Inc.