Singchat Worapong, Ahmad Syed Farhan, Sillapaprayoon Siwapech, Muangmai Narongrit, Duengkae Prateep, Peyachoknagul Surin, O'Connor Rebecca E, Griffin Darren K, Srikulnath Kornsorn
Laboratory of Animal Cytogenetics and Comparative Genomics (ACCG), Department of Genetics, Faculty of Science, Kasetsart University, Bangkok, Thailand.
Special Research Unit for Wildlife Genomics (SRUWG), Department of Forest Biology, Faculty of Forestry, Kasetsart University, Bangkok, Thailand.
Front Genet. 2020 Aug 18;11:948. doi: 10.3389/fgene.2020.00948. eCollection 2020.
Squamate reptile chromosome 2 (SR2) is thought to be an important remnant of an ancestral amniote super-sex chromosome, but a recent study showed that the Siamese cobra W sex chromosome is also a part of this larger ancestral chromosome. To confirm the existence of an ancestral amniote super-sex chromosome and understand the mechanisms of amniote sex chromosome evolution, chromosome maps of two snake species [Russell's viper: (DRU) and the common tiger snake: (NSC)] were constructed using bacterial artificial chromosomes (BACs) derived from chicken and zebra finch libraries containing amniote sex chromosomal linkages. Sixteen BACs were mapped on the W sex chromosome of DRU and/or NSC, suggesting that these BACs contained a common genomic region shared with the W sex chromosome of these snakes. Two of the sixteen BACs were co-localized to DRU2 and NSC2, corresponding to SR2. Prediction of genomic content from all BACs mapped on snake W sex chromosomes revealed a large proportion of long interspersed nuclear element (LINE) and short interspersed nuclear element (SINE) retrotransposons. These results led us to predict that amplification of LINE and SINE may have occurred on snake W chromosomes during evolution. Genome compartmentalization, such as transposon amplification, might be the key factor influencing chromosome structure and differentiation. Multiple sequence alignments of all BACs mapped on snake W sex chromosomes did not reveal common sequences. Our findings indicate that the SR2 and snake W sex chromosomes may have been part of a larger ancestral amniote super-sex chromosome, and support the view of sex chromosome evolution as a colorful myriad of situations and trajectories in which many diverse processes are in action.
有鳞目爬行动物的2号染色体（SR2）被认为是祖先羊膜动物超级性染色体的重要遗迹，但最近的一项研究表明，暹罗眼镜蛇的W性染色体也是这个更大的祖先染色体的一部分。为了证实祖先羊膜动物超级性染色体的存在，并了解羊膜动物性染色体进化的机制，利用来自鸡和斑胸草雀文库的细菌人工染色体（BAC）构建了两种蛇类[罗素蝰蛇：（DRU）和普通虎蛇：（NSC）]的染色体图谱，这些文库包含羊膜动物性染色体连锁。16个BAC被定位在DRU和/或NSC的W性染色体上，这表明这些BAC包含与这些蛇的W性染色体共有的一个常见基因组区域。16个BAC中的两个被共定位到DRU2和NSC2，对应于SR2。对定位在蛇W性染色体上的所有BAC的基因组内容预测显示，长散在核元件（LINE）和短散在核元件（SINE）反转录转座子占很大比例。这些结果使我们预测，在进化过程中，LINE和SINE可能在蛇的W染色体上发生了扩增。基因组的区室化，如转座子扩增，可能是影响染色体结构和分化的关键因素。定位在蛇W性染色体上的所有BAC的多序列比对未揭示共同序列。我们的研究结果表明，SR2和蛇的W性染色体可能是一个更大的祖先羊膜动物超级性染色体的一部分，并支持性染色体进化是一个丰富多彩的多种情况和轨迹的观点，其中许多不同的过程都在起作用。
