Molecular mechanisms of sex determination in birds

由于鸟类的性别决定和分化机制尚未解决，本项目旨在阐明鸡性腺性别分化的分子机制。睾丸产生抗苗勒氏激素(AMH)和雄激素，而卵巢产生少量AMH，但主要产生雌激素。我们的原位杂交研究表明，AMH mRNA在孵化第5天就开始表达，在孵化第6天急剧增加，随后保持不变。相比之下，雌性则表现出最低水平的表情。相反，雌性在孵化第6天就在性腺中表达了芳香酶，而雄性则很少表达。可能影响AMH和芳香酶基因的转录因子包括SOX 9、SF-1、DAX-1和DMRT-1。SOX-9mRNA主要在雄性性腺中表达，但在AMH表达后才表达。在孵化7.5d后，SF-1mRNA的表达呈性别二型性，雌性性腺中的表达高于雄性性腺。在鸡中，DAX-1mRNA在鸡的性腺中表达，无论性别。鸡Z染色体上的DMRT-1基因在性分化前的生殖脊和沃尔菲管中表达，且在雄性胚胎中的表达水平高于雌性胚胎。此外，在男性中，这是在AMH表达之前表达的。这种性别和时间特异性的表达使该基因成为参与鸟类性别决定的特别好的候选基因。

Since sex determination and differentiation mechanisms remain unsolved in birds, this project was conducted to elucidate the molecular mechanisms of sexual differentiation of the chicken gonad. The testis produces anti-Mullerian hormone (AMH) and androgen, whereas the ovary produces little AMH but produces estrogen predominantly. Our in situ hybridization study demonstrated that AMH mRNA was expressed as early as day 5 of incubation followed by a sharp increase on day 6 of incubation in males, which was subsequently maintained. In contrast, the female showed minimum levels of expression. Conversely, aromatase mRNA was expressed in the gonad as early as day 6 of incubation in female but little in the male. Possible transcription factors affecting the AMH and aromatase genes include Sox 9, Sf-1, Dax-1, and Dmrt-1. Sox 9 mRNA is predominantly expressed in male gonad, although it is expressed after the expression of AMH.The Sf-1 mRNA expression is sexually dimorphic after day 7.5 of incubation and expression is higher in the female gonad than in the male gonad. In the chicken Dax-1 mRNA is expressed in the chicken gonad in both sexes. Chicken Dmrt-1 gene on the Z chromosome was expressed in the genital ridge and Wolffian duct prior to sexual differentiation and is expressed at higher levels in male than in female embryos. Furthermore, this is expressed prior to AMH expression in male. This sex- and time-specific expression makes this gene an especially good candidate to be involved in avian sex determination.