Dorizzi M, Richard-Mercier N, Pieau C
Institut Jacques Monod, CNRS, Paris, France.
Differentiation. 1996 Jul;60(4):193-201. doi: 10.1046/j.1432-0436.1996.6040193.x.
Emys orbicularis is a turtle with temperature-dependent sex determination. The thermosensitive period (TSP) lies between embryonic stages 16 and 22. Gonadal differentiation begins during this period involving oestrogens. Treatment with oestrogens during TSP results in the differentiation of ovaries at a male-producing temperature (25 degrees C), whereas treatment with an antioestrogen (tamoxifen) or with nonsteroidal aromatase inhibitors results in gonadal masculinization at a female-producing temperature (30 degrees C). The present study examines the effects on the ovary of inhibiting aromatase activity after TSP. Eggs of E. orbicularis incubated at 30 degrees C were given five or seven applications of 10 micrograms aromatase inhibitor Letrozole (CGS 20267) in ethanol, between stages 22+ and 24-25 when ovarian aromatase activity strongly increases. Individuals which received five applications were sacrificed at stages 24(+)-25. Those which received seven applications were sacrificed either at stage 25+ (close to hatching), or 34-36 days after hatching. Gonadal aromatase activity and related gonadal structure were studied in each individual. In the three series, the gonadal aromatase activity in individuals treated with Letrozole varied from similar or close to that in controls to much lower, and the gonadal structure varied from ovary-like to ovotestis. Ovotestes had the lowest levels of aromatase activity, under 4 fmoles/h/gonad, close to testis levels. They were found in 7 out of 26 individuals given Letrozole. Besides ovotestes, gonads presenting various degrees of masculinization, with enlarged epithelial cords and lacunae in the medulla, were found. Therefore, by inhibiting aromatase activity and thus estrogen synthesis, we were able to obtain the differentiation of testis-like cords or tubes in ovaries of E. orbicularis, after the period of temperature sensitivity. These results show that the ovary retains male potential after this period. Thus, besides their implication during the critical embryonic period for gonadal sex differentiation, oestrogens play a role in maintaining the ovarian structure after this period. A decrease in oestrogen levels could explain some other cases of ovarian masculinization known in vertebrates.
欧洲池龟是一种具有温度依赖型性别决定的龟类。热敏期（TSP）处于胚胎发育的第16至22阶段之间。性腺分化在此期间开始，涉及雌激素。在热敏期用雌激素处理会导致在产生雄性的温度（25摄氏度）下卵巢分化，而用抗雌激素（他莫昔芬）或非甾体芳香化酶抑制剂处理会导致在产生雌性的温度（30摄氏度）下性腺雄性化。本研究考察了在热敏期后抑制芳香化酶活性对卵巢的影响。将在30摄氏度下孵化的欧洲池龟卵，在卵巢芳香化酶活性强烈增加的第22 +至24 - 25阶段之间，用乙醇给予5次或7次10微克芳香化酶抑制剂来曲唑（CGS 20267）处理。接受5次处理的个体在第24（+） - 25阶段处死。接受7次处理的个体在第25 +阶段（接近孵化时）或孵化后34 - 36天处死。对每个个体的性腺芳香化酶活性和相关性腺结构进行了研究。在这三个系列中，用他莫昔芬处理的个体的性腺芳香化酶活性从与对照组相似或接近到低得多不等，性腺结构从卵巢样到卵睾不等。卵睾的芳香化酶活性水平最低，低于4飞摩尔/小时/性腺，接近睾丸水平。在给予来曲唑的26个个体中有7个发现了卵睾。除了卵睾外，还发现了呈现不同程度雄性化的性腺，其髓质中的上皮索和腔隙增大。因此，通过抑制芳香化酶活性从而抑制雌激素合成，我们能够在温度敏感期过后，使欧洲池龟卵巢中出现睾丸样索或管的分化。这些结果表明，在此阶段过后卵巢仍保留雄性潜能。因此，除了它们在性腺性别分化的关键胚胎期所起的作用外，雌激素在此阶段过后还在维持卵巢结构方面发挥作用。雌激素水平的降低可以解释脊椎动物中已知的其他一些卵巢雄性化病例。
