Nagai T, Takehana Y, Hamaguchi S, Sakaizumi M
Graduate School of Science and Technology, Niigata University, Niigata, Japan.
Cytogenet Genome Res. 2008;121(2):137-42. doi: 10.1159/000125839. Epub 2008 Jun 9.
A sex-determining gene, DMY, which is comparable to the SRY gene in mammals, has been identified in the medaka, Oryzias latipes. Although Oryzias curvinotus, a closely related species to O. latipes also has DMY, this gene has not been found in other Oryzias fishes. It has recently been demonstrated that the sex chromosomes of Oryzias dancena and Oryzias hubbsi differ from those of O. latipes and these species have XX/XY and ZZ/ZW systems, respectively. This may suggest that Oryzias species have evolved different sex-determining genes on different sex chromosomes. In the present study, we investigated the sex determination mechanism in Oryzias minutillus, which is closely related to O. dancena and O. hubbsi. Linkage analysis using 14 isolated sex-linked DNA markers showed that this species has an XX/XY sex determination system. These sex-linked markers were located on linkage group 8 of O. latipes, suggesting that the sex chromosomes of O. minutillus are homologous to the autosomes of other Oryzias species. Furthermore, fluorescence in situ hybridization using a tightly sex-linked marker demonstrated that the XY sex chromosomes of O. minutillus and O. dancena were not homologous. These findings provide additional evidence for independent origins of sex chromosomes and sex-determining genes in these closely related species.
在青鳉（Oryzias latipes）中已鉴定出一种性别决定基因DMY，它与哺乳动物的SRY基因类似。尽管与青鳉亲缘关系密切的弯月鳉（Oryzias curvinotus）也有DMY，但在其他青鳉属鱼类中尚未发现该基因。最近有研究表明，丹氏青鳉（Oryzias dancena）和赫氏青鳉（Oryzias hubbsi）的性染色体与青鳉不同，且这两个物种分别具有XX/XY和ZZ/ZW性别决定系统。这可能表明青鳉属物种在不同的性染色体上进化出了不同的性别决定基因。在本研究中，我们调查了与丹氏青鳉和赫氏青鳉亲缘关系密切的小纹青鳉（Oryzias minutillus）的性别决定机制。使用14个分离的性连锁DNA标记进行连锁分析表明，该物种具有XX/XY性别决定系统。这些性连锁标记位于青鳉的连锁群8上，这表明小纹青鳉的性染色体与其他青鳉属物种的常染色体同源。此外，使用紧密性连锁标记进行的荧光原位杂交表明，小纹青鳉和丹氏青鳉的XY性染色体不同源。这些发现为这些亲缘关系密切的物种中性染色体和性别决定基因的独立起源提供了额外的证据。
