PDF(Pubmed)
Abstract：
In many groups, sex chromosomes change frequently but the drivers of their rapid evolution are varied and often poorly characterized. With an aim of further understanding sex chromosome turnover, we investigated the polymorphic sex chromosomes of the Marsabit clawed frog, Xenopus borealis, using genomic data and a new chromosome-scale genome assembly. We confirmed previous findings that 54.1 Mb of chromosome 8L is sex-linked in animals from east Kenya and a laboratory strain, but most (or all) of this region is not sex-linked in natural populations from west Kenya. Previous work suggests possible degeneration of the Z chromosomes in the east population because many sex-linked transcripts of this female heterogametic population have female-biased expression, and we therefore expected this chromosome to not be present in the west population. In contrast, our simulations support a model where most or all of the sex-linked portion of the Z chromosome from the east acquired autosomal segregation in the west, and where much genetic variation specific to the large sex-linked portion of the W chromosome from the east is not present in the west. These recent changes are consistent with the hot-potato model, wherein sex chromosome turnover is favoured by natural selection if it purges a (minimally) degenerate sex-specific sex chromosome, but counterintuitively suggest natural selection failed to purge a Z chromosome that has signs of more advanced and possibly more ancient regulatory degeneration. These findings highlight complex evolutionary dynamics of young, rapidly evolving Xenopus sex chromosomes and set the stage for mechanistic work aimed at pinpointing additional sex-determining genes in this group.
摘要：
在许多群体中,性染色体经常变化，但其快速进化的驱动因素各不相同，并且通常特征不佳。为了进一步了解性染色体更新，我们调查了马萨比特爪蛙的多态性染色体，北极熊,使用基因组数据和新的染色体尺度基因组组装。我们证实了先前的发现，在肯尼亚东部的动物和实验室菌株中，54.1Mb的8L染色体是性别相关的，但是该地区的大部分（或全部）在肯尼亚西部的自然人群中与性别无关。先前的工作表明东部人群中Z染色体可能退化，因为该女性异型基因人群的许多性别相关转录本具有女性偏向的表达，因此，我们预计这种染色体不会出现在西方人群中。相比之下,我们的模拟支持一个模型，其中来自东部的Z染色体的大部分或全部性别连锁部分在西部获得常染色体分离，在西部，不存在与东部W染色体的大性别连锁部分特有的许多遗传变异。这些最近的变化与烫手山芋模型是一致的，其中，如果自然选择清除（最小）退化的性别特异性性染色体，则自然选择有利于性染色体周转，但与直觉相反的是，自然选择未能清除Z染色体，该染色体具有更高级且可能更古老的调节退化的迹象。这些发现突出了年轻人复杂的进化动态，快速进化的非洲爪狼性染色体，并为旨在确定该组中其他性别决定基因的机械工作奠定了基础。
