Department of Biology, Faculty of Education and Integrated Arts and Sciences, Waseda University, Tokyo 162-8480, Japan.
Sex Dev. 2013;7(1-3):104-14. doi: 10.1159/000339661. Epub 2012 Jul 11.
Amphibians have 2 genetic sex-determining systems, one with male (XX/XY) and one with female (ZZ/ZW) heterogamety. While the ancestral state of sex-determination is thought to be female heterogamety, male and female heterogametic types were probably once interchangeable. The Japanese frog Rana rugosa has both XX/XY and ZZ/ZW systems within a single species in certain local populations. However, steroid hormones can alter the phenotypic sex epigenetically. In R. rugosa, steroidogenic enzyme expression starts before sex-determination in the indifferent gonad, and these enzymes become active in both male and female tadpoles. Androgens are produced in the indifferent gonad of male tadpoles at high levels, whereas estrogens are synthesized in females. In this regard, the observed enhanced expression of the hormone-metabolizing genes, CYP19 in the female gonad and CYP17 in males, may be crucial for sex-determination. Moreover, with FSH known to increase estrogen synthesis in the vertebrate ovary, observed upregulation of FSH receptor (FSHR) expression in the indifferent gonad of female tadpoles is intriguing. These data suggest that steroid hormones could be crucial for sex-determination in R. rugosa, with the consequence that upregulation of CYP19 and FSHR expression is necessary for female and CYP17 for male sex-determination.
两栖动物有两种遗传性别决定系统，一种是雄性（XX/XY），另一种是雌性（ZZ/ZW）异型配子。虽然性别决定的原始状态被认为是雌性异型配子，但雄性和雌性异型配子类型可能曾经是可互换的。日本青蛙 Rana rugosa 在某些局部种群的单一物种中同时具有 XX/XY 和 ZZ/ZW 系统。然而，类固醇激素可以通过表观遗传改变表型性别。在 R. rugosa 中，类固醇生成酶的表达在性别决定之前在中性性腺中开始，并且这些酶在雄性和雌性蝌蚪中都变得活跃。雄性蝌蚪的中性性腺中产生高水平的雄激素，而雌性则合成雌激素。在这方面，观察到激素代谢基因 CYP19 在雌性性腺和 CYP17 在雄性中的表达增强可能对性别决定至关重要。此外，由于已知 FSH 可增加脊椎动物卵巢中的雌激素合成，因此观察到 FSH 受体（FSHR）在雌性蝌蚪中性性腺中的表达上调令人着迷。这些数据表明，类固醇激素可能对 R. rugosa 的性别决定至关重要，因此 CYP19 和 FSHR 表达的上调对于雌性和 CYP17 对于雄性性别决定是必要的。
