Bögi Christian, Levy Gregor, Lutz Ilka, Kloas Werner
Department of Inland Fisheries, Leibniz-Institute of Freshwater Ecology, Müggelseedamm 310, 12587, Berlin, Germany.
Comp Biochem Physiol B Biochem Mol Biol. 2002 Dec;133(4):559-70. doi: 10.1016/s1096-4959(02)00162-8.
In Xenopus laevis the basic mechanisms underlying sexual differentiation were investigated by determining time courses of sexual steroids and their corresponding receptors during complete larval development from egg to juveniles. Androgens as well as estradiol (E2) are derived from maternal origin and accumulate in hatching tadpoles. Sexual steroid contents decreased rapidly after hatching and rose again at the end of metamorphosis indicating endogenous production. In parallel the mRNA expression for corresponding androgen (AR) and estrogen receptors (ER) was measured by means of semiquantitative RT-PCR. Both receptor mRNAs increased dramatically just after hatching and decreased only moderately until end of metamorphosis. In female juveniles E2 and ER-mRNA levels were higher compared with males. Treatment by exogenous E2 elevated both, ER- and AR-mRNA, indicating stimulatory functions of E2 for gene expression of both receptors. Effects on sexual differentiation during larval development were achieved by treatment with E2 and the antiandrogen cyproterone acetate both causing feminization, the antiestrogen tamoxifen resulting in neutralization, and the androgens, methyltestosterone and dihydrotestosterone, but not testosterone, leading to masculinization. The data presented are in accordance with further recent findings and suggest a new hypothesis for functional genomics in sexual differentiation of amphibians.
在非洲爪蟾中，通过测定从卵到幼体的整个幼体发育过程中性类固醇及其相应受体的时间进程，研究了性别分化的基本机制。雄激素以及雌二醇（E2）均源自母体，并在孵化后的蝌蚪中积累。孵化后性类固醇含量迅速下降，并在变态末期再次上升，表明存在内源性产生。同时，通过半定量逆转录聚合酶链反应测定相应雄激素受体（AR）和雌激素受体（ER）的mRNA表达。两种受体的mRNA在孵化后立即急剧增加，直到变态末期仅适度下降。在雌性幼体中，E2和ER-mRNA水平高于雄性。外源性E2处理可提高ER和AR-mRNA水平，表明E2对两种受体的基因表达具有刺激作用。在幼体发育过程中，通过用E2和抗雄激素醋酸环丙孕酮处理均可导致雌性化，用抗雌激素他莫昔芬处理导致中性化，而用雄激素甲基睾酮和二氢睾酮（而非睾酮）处理则导致雄性化。所呈现的数据与最近的进一步研究结果一致，并为两栖动物性别分化中的功能基因组学提出了一个新的假说。
