Evolution of the sex-determining gene using medaka fish and its related species

在大多数脊椎动物中，性别是由基因决定的。性别染色体细胞遗传学上分化良好的哺乳动物和鸟类具有共同的性别决定系统，而鱼类的性别决定机制是独立进化的，大多数具有遗传性别决定的物种具有未分化的性别染色体。性别决定基因Dmy仅在medaka鱼（Oryzias latipes）及其近亲之一O. curvinotus中被发现。分子系统发育分析表明，Dmy进化于O. latipes、O. curvinotus和O. luzonensis的共同祖先，然后在O. luzonensis中消失。在这里，我们证明了TGF-β超家族基因的y连锁等位基因Gsdf（性腺体细胞衍生生长因子）是O. luzonensis的性别决定基因。虽然Gsdf存在于两性染色体（GsdfY和GsdfX）上，但只有GsdfY在性别决定期表现出男性特有的高表达。Gsdf是medaka鱼性别决定级联中Dmy的下游基因，提示Gsdf独立于Dmy信号的新等位基因的出现导致O. luzonensis出现了一种新的性别决定基因。

In most vertebrate, sex is determined genetically. Mammals and birds with cytogenetically well-differentiated sex chromosome have common sex determination system in each class, while various sex-determination mechanisms have evolved independently in fishes, and most species with genetic sex determination have undifferentiated sex chromosomes. The sex-determining gene Dmy has only been found in medaka fish (Oryzias latipes) and one of its closest relatives O. curvinotus. Molecular phylogenetic analysis of these species suggested that Dmy evolved in the common ancestor of O. latipes, O. curvinotus and O. luzonensis and then disappeared in O. luzonensis.Here we demonstrated that Y-linked allele of a TGF-β superfamily gene, Gsdf (gonadal soma derived growth factor) functions as the sex-determining gene in O. luzonensis. Although Gsdf exists on both of the sex chromosomes (GsdfY and GsdfX), only GsdfY shows male specific high expression during sex determination period. Gsdf is a downstream gene of Dmy in the sex determination cascade of medaka fish, suggesting that emergence of new allele of Gsdf independent of Dmy signal has lead to appearance of a novel sex determining gene in O. luzonensis.