Institute for Applied Ecology, University of Canberra, Canberra, Australia.
Chromosome Res. 2009;17(8):965-73. doi: 10.1007/s10577-009-9102-6. Epub 2009 Dec 5.
Reptiles show a diverse array of sex chromosomal systems but, remarkably, the Z sex chromosomes of chicken are homologous to the ZW sex chromosomes of a species of gecko, Gekko hokouensis, suggesting an ancient but common origin. This is in contrast to the ZW sex chromosomes of snakes and a species of soft-shelled turtle, Pelodiscus sinensis, which are nonhomologous to those of chicken or each other and appear to have been independently derived. In this paper, we determine what homology, if any, the sex chromosomes of the Australian dragon lizard Pogona vitticeps shares with those of snake and chicken by mapping the dragon homologs of five snake Z chromosome genes (WAC, KLF6, TAX1BP1, RAB5A, and CTNNB1) and five chicken Z chromosome genes (ATP5A1, GHR, DMRT1, CHD1, and APTX) to chromosomes in the dragon. The dragon homologs of snake and chicken sex chromosome genes map to chromosomes 6 and chromosome 2, respectively, in the dragon and that DMRT1, the bird sex-determining gene, is not located on the sex chromosomes of P. vitticeps. Indeed, our data show that the dragon homolog to the chicken Z chromosome is likely to be wholly contained within chromosome 2 in P. vitticeps, which suggests that the sex-determining factor in P. vitticeps is not the sex-determining gene of chicken. Homology between chicken Z chromosome and G. hokouensis ZW chromosome pairs has been interpreted as retention of ancient ZW sex chromosomes in which case the nonhomologous sex chromosomes of snake and dragons would be independently derived. Our data add another case of independently derived sex chromosomes in a squamate reptile, which makes retention of ancient sex chromosome homology in the squamates less plausible. Alternatively, the conservation between the bird Z chromosome and the G. hokouensis ZW chromosomes pairs is coincidental, may be an example of convergent evolution, its status as the Z chromosome having been independently derived in birds and G. hokouensis.
爬行动物表现出多种多样的性染色体系统，但令人惊讶的是，鸡的 Z 性染色体与壁虎 Gekko hokouensis 的 ZW 性染色体同源，这表明它们具有古老而共同的起源。这与蛇和中华鳖 Pelodiscus sinensis 的 ZW 性染色体形成鲜明对比，后两者与鸡或彼此之间的 ZW 性染色体都没有同源性，似乎是独立衍生的。在本文中，我们通过将澳大利亚蜥蜴 Pogona vitticeps 的性染色体与蛇和鸡的同源基因进行映射，确定了蛇和鸡的性染色体与 Pogona vitticeps 的性染色体有何同源性（如果有的话）。我们将五个蛇 Z 染色体基因（WAC、KLF6、TAX1BP1、RAB5A 和 CTNNB1）和五个鸡 Z 染色体基因（ATP5A1、GHR、DMRT1、CHD1 和 APTX）的龙同源基因映射到龙的染色体上。蛇和鸡性染色体基因在龙中的同源基因分别位于第 6 号和第 2 号染色体上，而且鸟类性别决定基因 DMRT1 不在 Pogona vitticeps 的性染色体上。事实上，我们的数据表明，Pogona vitticeps 中鸡 Z 染色体的同源基因可能完全包含在第 2 号染色体中，这表明 Pogona vitticeps 的性别决定因素不是鸡的性别决定基因。鸡的 Z 染色体与 G. hokouensis ZW 染色体对之间的同源性被解释为古老的 ZW 性染色体的保留，在这种情况下，蛇和龙的非同源性性染色体是独立衍生的。我们的数据增加了另一个在有鳞目爬行动物中独立衍生的性染色体的例子，这使得有鳞目动物中古老的性染色体同源性的保留不太可信。或者，鸟类 Z 染色体与 G. hokouensis ZW 染色体对之间的保守性是偶然的，可能是趋同进化的一个例子，其在鸟类和 G. hokouensis 中的 Z 染色体地位是独立衍生的。
