Laopichienpong Nararat, Muangmai Narongrit, Chanhome Lawan, Suntrarachun Sunutcha, Twilprawat Panupon, Peyachoknagul Surin, Srikulnath Kornsorn
Laboratory of Animal Cytogenetics and Comparative Genomics (ACCG), Department of Genetics, Faculty of Science, Kasetsart University, 50 Ngamwongwan, Chatuchak, Bangkok, Thailand.
Department of Fishery Biology, Faculty of Fisheries, Kasetsart University, Bangkok, Thailand.
J Hered. 2017 Mar 1;108(2):142-151. doi: 10.1093/jhered/esw074.
Snakes exhibit genotypic sex determination with female heterogamety (ZZ males and ZW females), and the state of sex chromosome differentiation also varies among lineages. To investigate the evolutionary history of homologous genes located in the nonrecombining region of differentiated sex chromosomes in snakes, partial sequences of the gametologous CTNNB1 gene were analyzed for 12 species belonging to henophid (Cylindrophiidae, Xenopeltidae, and Pythonidae) and caenophid snakes (Viperidae, Elapidae, and Colubridae). Nonsynonymous/synonymous substitution ratios (Ka/Ks) in coding sequences were low (Ka/Ks < 1) between CTNNB1Z and CTNNB1W, suggesting that these 2 genes may have similar functional properties. However, frequencies of intron sequence substitutions and insertion–deletions were higher in CTNNB1Z than CTNNB1W, suggesting that Z-linked sequences evolved faster than W-linked sequences. Molecular phylogeny based on both intron and exon sequences showed the presence of 2 major clades: 1) Z-linked sequences of Caenophidia and 2) W-linked sequences of Caenophidia clustered with Z-linked sequences of Henophidia, which suggests that the sequence divergence between CTNNB1Z and CTNNB1W in Caenophidia may have occurred by the cessation of recombination after the split from Henophidia.
蛇类表现出基因型性别决定，雌性为异配子性别（ZZ为雄性，ZW为雌性），并且性染色体分化状态在不同谱系中也有所不同。为了研究蛇类分化性染色体非重组区域中同源基因的进化历史，分析了12种蛇的同源CTNNB1基因的部分序列，这些蛇分别属于盲蛇亚目（筒蛇科、异盾盲蛇科和蟒科）和新蛇亚目（蝰蛇科、眼镜蛇科和游蛇科）。CTNNB1Z和CTNNB1W编码序列中的非同义/同义替换率（Ka/Ks）较低（Ka/Ks < 1），表明这两个基因可能具有相似的功能特性。然而，CTNNB1Z中内含子序列替换和插入 - 缺失的频率高于CTNNB1W，这表明Z连锁序列比W连锁序列进化得更快。基于内含子和外显子序列的分子系统发育显示存在两个主要分支：1）新蛇亚目的Z连锁序列和2）新蛇亚目的W连锁序列与盲蛇亚目的Z连锁序列聚类，这表明新蛇亚目CTNNB1Z和CTNNB1W之间的序列分歧可能是在与盲蛇亚目分化后重组停止而发生的。
