Cortisol is involved in temperature-dependent sex determination in the Japanese flounder.

In vertebrates, sex is normally determined by genotype. However, in poikilothermal vertebrates, including reptiles, amphibians, and fishes, sex determination is greatly influenced by environmental factors, such as temperature. Little is known about the molecular mechanisms underlying environmental sex determination in these species.

Mullerian inhibiting substance is required for germ cell proliferation during early gonadal differentiation in medaka (Oryzias latipes).

Müllerian inhibiting substance (MIS) is a glycoprotein belonging to the TGF-beta superfamily. In mammals, MIS is responsible for the regression of Müllerian ducts in the male fetus. However, the role of MIS in gonadal sex differentiation of teleost fish, which have no Müllerian ducts, has yet to be clarified.

Tamoxifen induces masculinization of genetic females and regulates P450 aromatase and Müllerian inhibiting substance mRNA expression in Japanese flounder (Paralichthys olivaceus).

Japanese flounder, Paralichthys olivaceus, provides an excellent model to elucidate the roles of sex steroid hormones in gonadal sex differentiation because the sex is easily altered by sex steroid treatments or water temperature control during the sex differentiation. We have previously shown that high water temperature, an aromatase inhibitor (fadrozole), or 17alpha-methyltestosterone treatment causes the sex-reversal from genetic females to phenotypic males and suppression of mRNA expression of ovary-type P450 aromatase (P450arom), which is a steroidogenic enzyme responsible for the conversion of androgens to estrogens, in Japanese flounder. In the present study, we demonstrate that treatment of the genetic females with anti-estrogen (tamoxifen) leads to their masculinization, suppresses P450arom mRNA expression, and induces mRNA expression of Müllerian inhibiting substance (MIS), a member of the transforming growth factor-beta (TGF-beta) superfamily, while it has no effect on mRNAs expression of estrogen receptor-alpha (ERalpha) and ERbeta.

Sexually dimorphic expression of a teleost homologue of Müllerian inhibiting substance during gonadal sex differentiation in Japanese flounder, Paralichthys olivaceus.

Müllerian inhibiting substance (MIS), also known as anti-Müllerian hormone, is a glycoprotein belonging to transforming growth factor beta superfamily. In mammals, MIS is responsible for regression of Müllerian ducts, anlagen of the female reproductive ducts, in the male fetus. However, the role of MIS in gonadal sex differentiation of teleost fishes, which do not have the Müllerian ducts, has yet to be clarified.