Florida Museum of Natural History, University of Florida, Gainesville, FL 32611, USA.
Department of Biological Sciences, Marquette University, Milwaukee, WI 53201, USA.
Biol Lett. 2019 Oct 31;15(10):20190498. doi: 10.1098/rsbl.2019.0498. Epub 2019 Oct 9.
Most pleurodont lizard families (anoles, iguanas and their relatives), with the exception of the basilisks and casquehead lizards (family Corytophanidae), share homologous XX/XY sex chromosomes, syntenic with chicken chromosome 15. Here, we used a suite of methods (i.e. RADseq, RNAseq and qPCR) to identify corytophanid sex chromosomes for the first time. We reveal that all examined corytophanid species have partially degenerated XX/XY sex chromosomes, syntenic with chicken chromosome 17. Transcriptomic analyses showed that the expression of X-linked genes in the corytophanid, is not balanced between the sexes, which is rather exceptional under male heterogamety, and unlike the dosage-balanced sex chromosomes in other well-studied XX/XY systems, including the green anole, . Corytophanid sex chromosomes may represent a rare example of a turnover away from stable, differentiated sex chromosomes. However, because of poor phylogenetic resolution among pleurodont families, we cannot reject the alternative hypothesis that corytophanid sex chromosomes evolved independently from an unknown ancestral system.
大多数有鳞目蜥蜴科（变色龙、鬣蜥及其亲属），除了巨蜥和盔头蜥科（盔头蜥科），都具有同源的 XX/XY 性染色体，与鸡的 15 号染色体同线性。在这里，我们首次使用了一系列方法（即 RADseq、RNAseq 和 qPCR）来鉴定盔头蜥科的性染色体。我们揭示了所有被检查的盔头蜥科物种的 XX/XY 性染色体都有部分退化，与鸡的 17 号染色体同线性。转录组分析表明，在盔头蜥科中，X 连锁基因的表达在性别之间是不平衡的，这在雄性异型配子中是相当特殊的，与其他研究充分的 XX/XY 系统中的剂量平衡性染色体不同，包括绿色变色龙。盔头蜥科的性染色体可能代表了一个罕见的例子，即从稳定的、分化的性染色体中脱离出来。然而，由于有鳞目蜥蜴科之间的系统发育分辨率较差，我们不能排除盔头蜥科的性染色体是从一个未知的祖先系统独立进化而来的替代假说。
