Follicle-stimulating hormone signaling and Foxl2 are involved in transcriptional regulation of aromatase gene during gonadal sex differentiation in Japanese flounder, Paralichthys olivaceus

Japanese flounder (Paralichthys olivaceus), a teleost fish that has XX (female)/XY (male) sex determination system, exhibits temperature-dependent sex determination. We have previously shown that high water temperature or an aromatase inhibitor treatment causes the sex-reversal from genetic females to phenotypic males and suppression of mRNA expression of ovary-type P450 aromatase (cyp19a1), a steroidogenic enzyme responsible for the conversion of androgens to estrogens, in Japanese flounder. In the present study, we demonstrate that high water temperature treatment suppresses specifically mRNA expression of the forkhead transcription factor gene foxl2, and follicle-stimulating hormone receptor (fshr) in gonads during early sex differentiation. Moreover, transient transfection assay shows that the flounder Foxl2 and cAMP analog can activate the cyp19a1 gene transcription in vitro. These results strongly suggest that FSH signaling and Foxl2 are involved in the transcriptional regulation of cyp19a1 gene during gonadal sex differentiation in Japanese flounder with temperature-dependent sex determination.