Sex chromosome evolution in snakes inferred from divergence patterns of two gametologous genes and chromosome distribution of sex chromosome-linked repetitive sequences.
Sex chromosome evolution in snakes inferred from divergence patterns of two gametologous genes and chromosome distribution of sex chromosome-linked repetitive sequences.
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DOI：
10.1186/s40851-016-0056-1
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发表时间：
2016
影响因子：
2.7
通讯作者：
Kumazawa Y
中科院分区：
文献类型：
--
作者：
Matsubara K;Nishida C;Matsuda Y;Kumazawa Y
不同组织性染色体系统的发现表明，异型性染色体是从一对同源染色体进化而来的。尽管蛇的核型高度保守，但W染色体的退化状态在不同物种之间有所不同。蛇科蛇的Z染色体和W染色体形态同态，而蛇科蛇的W染色体则高度退化。因此，蛇是研究性染色体进化的绝佳动物模型。本文采用编码序列和重复序列两种方法研究了蛇性染色体的分化过程。本文分析了蛇性染色体长臂上CTNNB1和WAC基因（分别位于着丝粒区和端粒区）的系统发育关系，以及性染色体连锁重复序列在一些嗜蛇和嗜蛇物种中的分布。结果表明，CTNNB1和WAC编码序列分别用于棘蝽科、圆蝽科、圆蝽科、爪蝽科和蟒蛇科的Z种和棘蝽科、蝮蛇科、舌蝽科和刺蝽科的Z和W种。这两个基因的雌性特异性序列未在研究的嗜蛇目动物（boid和pythonid）物种中发现。利用每个基因构建的系统发育树显示，Z和W同源物种分别聚集在一起。从四角叶猴（Elaphe quadrivirgata）的W染色体异染色质中分离到的重复序列和微卫星基序（AGAT）8与所检测的蛇形和杂交种的W染色体进行了强杂交。我们的系统发育分析表明，CTNNB1和WAC的Z和W同源基因之间的重组停止早于栉水母家族的多样化。由于W染色体上的重复序列在蛇形和色系物种中是共享的，因此原W染色体的异染色化似乎发生在这两个群体分裂之前。这些结果共同表明，在相对较短的时间内，原始z染色体和原始w染色体的分化扩展到性染色体上的广泛区域。本文的在线版本（doi:10.1186/s40851-016-0056-1）包含补充材料，可供授权用户使用。
The discovery of differentially organized sex chromosome systems suggests that heteromorphic sex chromosomes evolved from a pair of homologous chromosomes. Whereas karyotypes are highly conserved in alethinophidian snakes, the degeneration status of the W chromosomes varies among species. The Z and W chromosomes are morphologically homomorphic in henophidian species, whereas in snakes belonging to caenophidian families the W chromosomes are highly degenerated. Snakes therefore are excellent animal models in which to study sex chromosome evolution. Herein, we investigated the differentiation processes for snake sex chromosomes using both coding and repetitive sequences. We analyzed phylogenetic relationships of CTNNB1 and WAC genes, localized to the centromeric and telomeric regions, respectively, of the long arms on snake sex chromosomes, and chromosome distribution of sex chromosome-linked repetitive sequences in several henophidian and caenophidian species. Partial or full-length coding sequences of CTNNB1 and WAC were identified for Z homologs of henophidian species from Tropidophiidae, Boidae, Cylindrophiidae, Xenopeltidae, and Pythonidae, and for Z and W homologs of caenophidian species from Acrochordidae, Viperidae, Elapidae, and Colubridae. Female-specific sequences for the two genes were not found in the henophidian (boid and pythonid) species examined. Phylogenetic trees constructed using each gene showed that the Z and W homologs of the caenophidian species cluster separately. The repetitive sequence isolated from the W chromosome heterochromatin of the colubrid Elaphe quadrivirgata and a microsatellite motif (AGAT)8 were strongly hybridized with W chromosomes of the viperid and colubrid species examined. Our phylogenetic analyses suggest that the cessation of recombination between the Z and W homologs of CTNNB1 and WAC predated the diversification of the caenophidian families. As the repetitive sequences on the W chromosomes were shared among viperid and colubrid species, heterochromatinization of the proto-W chromosome appears to have occurred before the splitting of these two groups. These results collectively suggest that differentiation of the proto-Z and proto-W chromosomes extended to wide regions on the sex chromosomes in the common ancestor of caenophidian families during a relatively short period. The online version of this article (doi:10.1186/s40851-016-0056-1) contains supplementary material, which is available to authorized users.