Iwamatsu Takashi, Kobayashi Hirokuni, Sagegami Reiko, Shuo Takuya
Department of Biology, Aichi University of Education, Kariya 448-8542, Japan.
Gen Comp Endocrinol. 2006 Jan 1;145(1):67-74. doi: 10.1016/j.ygcen.2005.07.003. Epub 2005 Aug 30.
To understand the effect of testosterone on sex differentiation, the quantities of testosterone (T) and estradiol-17beta (E2) in developing eggs of medaka (Oryzias latipes) were measured by radioimmunoassay, and the influence on sex differentiation of treating embryos with exogenous androgens was also examined. Endogenous T of eggs dispersed into the environmental water at spawning, and precipitously declined to a minimum level during incubation for 2 days post-fertilization (dpf). It did not significantly increase during development. The E2 content of fertilized eggs increased when eggs were incubated in medium containing exogenous T at the concentrations of 100 and 500 ng/ml, but not in low concentrations of 10 ng/ml or less. The presence of 500 ng/ml 17alpha-methyltestosterone (MT) in the incubation medium also induced an increase in the E2 content of embryos. Exposure of embryos to exogenous 1 ng/ml T that corresponded with the level of T in eggs shortly after fertilization was enough to induce sex reversal of genotypic females to functional males. The co-existence of T and aromatase inhibitor in incubation medium inhibited not only the T-induced increase in the embryonic E2 content, but also the estrogenic effect of T in causing the paradoxical sex reversal from genotypic males to phenotypic females. However, treatment of embryos with the non-aromatizable androgen, 17alpha-methyldihydrotestosterone, induced no detectable increase in the E2 content of embryos, but still brought about sex reversal of genotypic males into females. This contradictory result suggests that the conversion of androgens to E2 may not always be the cause for induction of paradoxical sex reversal by T treatment. Consequently, these results on sex reversal induced by treatment of embryos with exogenous androgens suggest that endogenous T of developing medaka embryos may not act as the natural andro-inducer, and that genotypic sex can be modified by exogenous sex steroids at early developmental stages long before gonadal differentiation in the medaka.
为了解睾酮对性别分化的影响，通过放射免疫分析法测定了青鳉（Oryzias latipes）发育中卵内睾酮（T）和雌二醇-17β（E2）的含量，并研究了用外源性雄激素处理胚胎对性别分化的影响。产卵时，卵内的内源性T分散到环境水中，并在受精后2天（dpf）的孵化过程中急剧下降至最低水平。在发育过程中它没有显著增加。当卵在含有100和500 ng/ml浓度外源性T的培养基中孵化时，受精卵的E2含量增加，但在10 ng/ml或更低的低浓度下则没有增加。孵育培养基中存在500 ng/ml的17α-甲基睾酮（MT）也会导致胚胎E2含量增加。将胚胎暴露于与受精后不久卵内T水平相当的1 ng/ml外源性T中，就足以诱导基因型雌性向功能性雄性的性逆转。孵育培养基中T和芳香化酶抑制剂的共存不仅抑制了T诱导的胚胎E2含量增加，也抑制了T导致基因型雄性向表型雌性的矛盾性性逆转的雌激素效应。然而，用不可芳香化的雄激素17α-甲基二氢睾酮处理胚胎，并未检测到胚胎E2含量增加，但仍导致基因型雄性向雌性的性逆转。这一矛盾结果表明，雄激素向E2的转化可能并不总是T处理诱导矛盾性性逆转的原因。因此，这些关于用外源性雄激素处理胚胎诱导性逆转的结果表明，发育中的青鳉胚胎内源性T可能并非天然雄激素诱导剂，并且在青鳉性腺分化很早之前的早期发育阶段，外源性性类固醇就可以改变基因型性别。
