Department of Genetics, Evolution and Environment, University College London, London WC1E 6BT, United Kingdom;
Department of Animal and Plant Sciences, University of Sheffield, Sheffield S10 2TN, United Kingdom.
Proc Natl Acad Sci U S A. 2019 Sep 17;116(38):19031-19036. doi: 10.1073/pnas.1905298116. Epub 2019 Sep 4.
Once recombination is halted between the X and Y chromosomes, sex chromosomes begin to differentiate and transition to heteromorphism. While there is a remarkable variation across clades in the degree of sex chromosome divergence, far less is known about the variation in sex chromosome differentiation within clades. Here, we combined whole-genome and transcriptome sequencing data to characterize the structure and conservation of sex chromosome systems across Poeciliidae, the livebearing clade that includes guppies. We found that the XY system is much older than previously thought, being shared not only with its sister species, , but also with , which diverged roughly 20 million years ago. Despite the shared ancestry, we uncovered an extreme heterogeneity across these species in the proportion of the sex chromosome with suppressed recombination, and the degree of Y chromosome decay. The sex chromosomes in and are largely homomorphic, with recombination in the former persisting over a substantial fraction. However, the sex chromosomes in are completely nonrecombining and strikingly heteromorphic. Remarkably, the profound degradation of the ancestral Y chromosome in is counterbalanced by the evolution of functional chromosome-wide dosage compensation in this species, which has not been previously observed in teleost fish. Our results offer important insight into the initial stages of sex chromosome evolution and dosage compensation.
一旦 X 和 Y 染色体之间的重组停止，性染色体就开始分化并转变为异型。虽然在不同进化枝之间，性染色体的分化程度有很大的差异，但关于进化枝内性染色体分化的变化知之甚少。在这里，我们结合全基因组和转录组测序数据，描述了包括孔雀鱼在内的单孔目鱼类的性染色体系统的结构和保守性。我们发现，XY 系统比以前认为的要古老得多，不仅与姐妹物种 共享，而且还与 共享，后者大约在 2000 万年前分化。尽管有共同的祖先，但我们在这些物种中发现了重组抑制的性染色体比例以及 Y 染色体退化程度的极端异质性。 和 的性染色体在很大程度上是同形的，前者的重组在很大程度上持续存在。然而， 的性染色体完全没有重组，而且非常异型。值得注意的是，在 中，祖先 Y 染色体的严重退化被该物种中功能上的全染色体剂量补偿所平衡，这在以前的硬骨鱼中没有观察到。我们的研究结果为性染色体进化和剂量补偿的初始阶段提供了重要的见解。
