Rovatsos M, Vukić J, Kratochvíl L
Department of Ecology, Faculty of Science, Charles University in Prague, Prague, Czech Republic.
Heredity (Edinb). 2016 Jul;117(1):8-13. doi: 10.1038/hdy.2016.18. Epub 2016 Mar 16.
Among amniotes, squamate reptiles are especially variable in their mechanisms of sex determination; however, based largely on cytogenetic data, some lineages possess highly evolutionary stable sex chromosomes. The still very limited knowledge of the genetic content of squamate sex chromosomes precludes a reliable reconstruction of the evolutionary history of sex determination in this group and consequently in all amniotes. Female heterogamety with a degenerated W chromosome typifies the lizards of the family Lacertidae, the widely distributed Old World clade including several hundreds of species. From the liver transcriptome of the lacertid Takydromus sexlineatus female, we selected candidates for Z-specific genes as the loci lacking single-nucleotide polymorphisms. We validated the candidate genes through the comparison of the copy numbers in the female and male genomes of T. sexlineatus and another lacertid species, Lacerta agilis, by quantitative PCR that also proved to be a reliable technique for the molecular sexing of the studied species. We suggest that this novel approach is effective for the detection of Z-specific and X-specific genes in lineages with degenerated W, respectively Y chromosomes. The analyzed gene content of the Z chromosome revealed that lacertid sex chromosomes are not homologous with those of other reptiles including birds, but instead the genes have orthologs in the X-conserved region shared by viviparous mammals. It is possible that this part of the vertebrate genome was independently co-opted for the function of sex chromosomes in viviparous mammals and lacertids because of its content of genes involved in gonad differentiation.
在羊膜动物中，有鳞目爬行动物的性别决定机制差异极大；然而，主要基于细胞遗传学数据，一些谱系拥有高度进化稳定的性染色体。由于对有鳞目性染色体遗传内容的了解仍然非常有限，因此无法可靠地重建该类群以及所有羊膜动物的性别决定进化史。具有退化W染色体的雌性异配性别是蜥蜴科蜥蜴的典型特征，蜥蜴科是广泛分布于旧大陆的一个类群，包含数百个物种。从雌性草绿龙蜥的肝脏转录组中，我们选择了缺乏单核苷酸多态性的Z特异性基因候选基因。我们通过定量PCR比较了草绿龙蜥和另一种蜥蜴物种捷蜥蜴的雌性和雄性基因组中的拷贝数，对候选基因进行了验证，定量PCR也被证明是对所研究物种进行分子性别鉴定的可靠技术。我们认为，这种新方法分别对于检测具有退化W或Y染色体谱系中的Z特异性基因和X特异性基因是有效的。对Z染色体分析的基因内容表明，蜥蜴科的性染色体与包括鸟类在内的其他爬行动物的性染色体不同源，而是这些基因在胎生哺乳动物共有的X保守区域中有直系同源基因。由于该区域包含参与性腺分化的基因，脊椎动物基因组的这一部分有可能在胎生哺乳动物和蜥蜴科动物中被独立地用于性染色体的功能。
