Torres Maldonado L C, Landa Piedra A, Moreno Mendoza N, Marmolejo Valencia A, Meza Martínez A, Merchant Larios H
Department of Cell Biology and Phisiology, Instituto de Investigaciones Biomédicas, Ciudad Universitaria, UNAM Apartado Postal 70228, C.P. 04510, México, DF, Mexico.
Gen Comp Endocrinol. 2002 Oct 15;129(1):20-6. doi: 10.1016/s0016-6480(02)00511-7.
Sex determination is controlled either by genetic or environmental factors. In mammals Sry initiates determination but no homologue of this gene exists in non-mammalian species. Other genes of the mammalian sex-determining pathway have been identified in gonads of different vertebrates. Sox9, Dax1, and Dmrt1 are expressed at the onset of gonadal development in birds and reptiles. In the sea turtle Lepidochelys olivacea, a species with temperature sex determination (TSD), Sox9 is expressed in undifferentiated gonads at male- (MPT) or female-promoting temperatures (FPT). At MPT, Sox9 remains expressed in male gonads, but at FPT it is downregulated coinciding with the onset of the ovarian morphologic differentiation and female sex determination. At MPT however, male sex is determined early than at FPT in still undifferentiated gonads suggesting that other genes maintain Sox9 expression in testis. Here we used RT-PCR to study the expression profiles of Dax1, Dmrt1, and Sox9 in gonads of embryos of L. olivacea incubated at MPT or at FPT. The profiles were correlated with sex determination during and after the temperature-sensitive period (TSP). Dax1 maintained similar levels at both temperatures during the TSP. The Dax1 expression level increased significantly in ovaries compared to testes at stage 27, once they were morphologically distinct. The expression levels of Dmrt1 were higher at MPT than at FPT at all stages, in contrast with Sox9 levels which were similar at both temperatures at stages 23-25. Together, current results suggest that, whereas Dax1 is not involved in TSD in L. olivacea, upregulation of Dmrt1 and downregulation of Sox9 may play a role in male and female sex determination, respectively.
性别决定受遗传或环境因素控制。在哺乳动物中，Sry启动性别决定，但该基因在非哺乳动物物种中不存在同源物。哺乳动物性别决定途径中的其他基因已在不同脊椎动物的性腺中被鉴定出来。Sox9、Dax1和Dmrt1在鸟类和爬行动物性腺发育开始时表达。在具有温度依赖型性别决定（TSD）的绿海龟中，Sox9在雄性促进温度（MPT）或雌性促进温度（FPT）下的未分化性腺中表达。在MPT时，Sox9在雄性性腺中持续表达，但在FPT时，它随着卵巢形态分化和雌性性别决定的开始而下调。然而，在MPT时，在仍未分化的性腺中，雄性性别比在FPT时更早确定，这表明其他基因维持Sox9在睾丸中的表达。在这里，我们使用逆转录聚合酶链反应（RT-PCR）来研究在MPT或FPT下孵化的绿海龟胚胎性腺中Dax1、Dmrt1和Sox9的表达谱。这些表达谱与温度敏感期（TSP）期间及之后的性别决定相关。在TSP期间，Dax1在两种温度下维持相似水平。在第27阶段，一旦卵巢和睾丸在形态上不同，卵巢中Dax1的表达水平与睾丸相比显著增加。在所有阶段，Dmrt1在MPT时的表达水平高于FPT，而Sox9在第23 - 25阶段在两种温度下水平相似。总之，目前的结果表明，虽然Dax1不参与绿海龟的TSD，但Dmrt1的上调和Sox9的下调可能分别在雄性和雌性性别决定中起作用。
