Departamento de Embriología, Facultad de Medicina, UNAM. México DF, Mexico City, Mexico.
Dev Biol. 2012 Jan 1;361(1):156-66. doi: 10.1016/j.ydbio.2011.10.001. Epub 2011 Oct 8.
Bipotential gonads represent the structural framework from which alternative molecular sex determination networks have evolved. Maintenance of Sox9 expression in Sertoli cells is required for the structural and functional integrity of male gonads in mammals and probably in most amniote vertebrates. However, spatial and temporal patterns of Sox9 expression have diversified along evolution. Species with temperature sex determination are an interesting predictive model since one of two alternative developmental outcomes, either ovary or testis occurs under controlled laboratory conditions. In the sea turtle Lepidochelys olivacea, Sox9 is expressed in the medullary cords of bipotential gonads when incubated at both female- or male-promoting temperature (FT or MT). Sox9 is then turned off in presumptive ovaries, while it remains turned on in testes. In the current study, Sox9 was used as a marker of the medullary cell lineage to investigate if the medullary cords originate from mesothelial cells at the genital ridges where Sox9 is upregulated, or, if they derive from a cell population specified at an earlier developmental stage, which maintains Sox9 expression. Using immunofluorescence and in situ hybridization, embryos were analyzed prior to, during and after gonadal sex determination. A T-shaped domain (T-Dom) formed by cytokeratin (CK), N-cadherin (Ncad) and SOX9-expressing cells was found at the upper part of the hindgut dorsal mesentery. The arms of the T-Dom were extended to both sides towards the ventromedial mesonephric ridge before the thickening of the genital ridges, indicating that they contained gonadal epithelial cell precursors. Thereafter, expression of Sox9 was maintained in medullary cords while it was downregulated at the surface epithelium of bipotential gonads in both FT and MT. This result contrasts with observations in mammals and birds, in which Sox9 upregulation starts at a later stage in the inner cells underlying the Sox9-negative surface epithelium, suggesting that the establishment of a self-regulatory Sox9 loop required for Sertoli cell determination has evolved. The T-shaped domain at the upper part of the hindgut dorsal mesentery found in the current study may represent the earliest precursor of the genital ridges, previously unnoticed in amniote vertebrates.
双潜能性腺代表了从其中进化出替代分子性别决定网络的结构框架。Sox9 蛋白在哺乳动物睾丸中支持 Sertoli 细胞的结构和功能完整性，这对于大多数羊膜动物的雄性性腺都是必需的。然而，Sox9 蛋白的表达空间和时间模式在进化过程中已经多样化。具有温度性别决定的物种是一个有趣的预测模型，因为在受控实验室条件下，两种替代发育结果之一，卵巢或睾丸，都会发生。在海龟 Lepidochelys olivacea 中，当在雌性或雄性促进温度（FT 或 MT）下孵育时，Sox9 蛋白在双潜能性腺的髓索中表达。然后，Sox9 蛋白在预期的卵巢中关闭，而在睾丸中保持打开。在本研究中，Sox9 蛋白被用作髓索细胞谱系的标志物，以研究髓索是否来源于生殖嵴中高表达 Sox9 蛋白的间皮细胞，或者它们是否来自于在更早的发育阶段就已指定的细胞群，该细胞群维持 Sox9 蛋白的表达。通过免疫荧光和原位杂交技术，在性腺性别决定之前、期间和之后分析胚胎。在 Hindgut 背系膜的上部发现了一个由细胞角蛋白 (CK)、N-钙黏蛋白 (Ncad) 和 Sox9 蛋白表达细胞组成的 T 形域 (T-Dom)。在生殖嵴变厚之前，T-Dom 的臂向两侧延伸到中肾旁内侧嵴，表明它们包含性腺上皮细胞前体。此后，Sox9 蛋白在髓索中保持表达，而在 FT 和 MT 中的双潜能性腺表面上皮中表达下调。这一结果与哺乳动物和鸟类的观察结果相反，在哺乳动物和鸟类中，Sox9 蛋白的上调始于 Sox9 蛋白阴性表面上皮下的内层细胞中的较晚阶段，这表明为支持 Sertoli 细胞决定所需的自我调节 Sox9 环的建立已经进化。在当前研究中在 Hindgut 背系膜上部发现的 T 形域可能代表了以前在羊膜动物中未被注意到的生殖嵴的最早前体。
