A role of the Sox 9 gene in amphibian sex determination

Sox是一个与SRY相关的睾丸决定基因家族。我们从成年青蛙睾丸cDNA文库中分离到两种不同的青蛙Sox 9基因mRNA亚型。一种形式（Sox 9 α）编码含有HMG盒的482个氨基酸的蛋白质，而另一种（Sox 9 β）完全缺乏HMG盒，是Sox 9 α的N末端截短的265个氨基酸的蛋白质。Sox 9 α在氨基酸水平上与小鼠、鸡和鳟鱼Sox 9s的相似性分别为82%、86%和77%。在系统发育树中，蛙Sox 9与鳟鱼Sox 9明显分化，其次是鸡和龟Sox 9。Sox 9在16期以后的胚胎中表达上调，并且在分化中的睾丸和卵巢中均可见。通过北方印迹分析确定Sox 9转录物的大小为7.8 knt。Sox 9 α在成年蛙的睾丸和脑组织中的表达量明显高于Sox 9 β。Sox 9在两性性腺发育的早期阶段表达，但在雌性中较早下降。这与鸟类和哺乳动物中的模式不同，其中Sox 9的表达是雄性特异性的。此外，Sox 9 α和9 β在雌性转雄性蝌蚪的性腺中表达上调。综上所述，这些结果表明，Sox 9参与了两栖动物的睾丸分化。由于Sox 9在青蛙性腺发育早期的睾丸和卵巢中都有表达，因此其作用可能与鸟类和哺乳动物不同。

Sox is a family of SRY-related testis-determining genes. We have isolated two different mRNA isoforms of the frog Sox9 gene from adult frog testis cDNA library. One form (Sox9 α) encodes a 482-amino acid protein containing the HMG box, whereas the other (Sox9 β), which completely lacks the HMG box, is a N-terminal truncated 265-amino acid protein of Sox9 α. Sox9 α is 82 % similar to mouse, 86 % to chicken, and 77 % to trout Sox9s at the amino acid level. In the phylogenetic tree, frog Sox9 was clearly diverged from trout Sox9, and then from chicken and turtle Sox9s. The Sox9 expression was up-regulated in embryos after stage 16, and was seen in both differentiating testis and ovary. The size of Sox9 transcripts was determined to be 7.8 knt by Northern blot analysis. In addition, The expression of Sox9 α was dominant in the testis and brain among various tissues of adult frogs examined, and was considerably higher than that of Sox9 β. Sox9 is expressed at early stages of gonadal development in both sexes, but declined earlier in females. This is dissimilar to the pattern in birds and mammals, in which Sox9 expression is male-specific. In addition, Sox9 α and 9 β expressions were up-regulated in the gonad of female-to-male sex-reversed tadpoles. Taken together, the results suggest that the Sox9 is involved in testicular differentiation of amphibians. Since the Sox9 expression is found in both the testis and ovary of frogs at early stages of gonadal development, its role is probably different from that in birds and mammals.