Department of Zoology, University of Oxford, Oxford, United Kingdom.
School of Natural Sciences, Bangor University, Bangor, Gwynedd, United Kingdom.
Mol Biol Evol. 2020 Aug 1;37(8):2197-2210. doi: 10.1093/molbev/msaa072.
Recombination increases the local GC-content in genomic regions through GC-biased gene conversion (gBGC). The recent discovery of a large genomic region with extreme GC-content in the fat sand rat Psammomys obesus provides a model to study the effects of gBGC on chromosome evolution. Here, we compare the GC-content and GC-to-AT substitution patterns across protein-coding genes of four gerbil species and two murine rodents (mouse and rat). We find that the known high-GC region is present in all the gerbils, and is characterized by high substitution rates for all mutational categories (AT-to-GC, GC-to-AT, and GC-conservative) both at synonymous and nonsynonymous sites. A higher AT-to-GC than GC-to-AT rate is consistent with the high GC-content. Additionally, we find more than 300 genes outside the known region with outlying values of AT-to-GC synonymous substitution rates in gerbils. Of these, over 30% are organized into at least 17 large clusters observable at the megabase-scale. The unusual GC-skewed substitution pattern suggests the evolution of genomic regions with very high recombination rates in the gerbil lineage, which can lead to a runaway increase in GC-content. Our results imply that rapid evolution of GC-content is possible in mammals, with gerbil species providing a powerful model to study the mechanisms of gBGC.
重组通过 GC 偏向的基因转换 (gBGC) 在基因组区域增加局部 GC 含量。最近在肥胖沙鼠 Psammomys obesus 中发现了一个具有极端 GC 含量的大型基因组区域，为研究 gBGC 对染色体进化的影响提供了模型。在这里，我们比较了四种沙鼠和两种鼠类（鼠和大鼠）的四个蛋白编码基因中的 GC 含量和 GC 到 AT 取代模式。我们发现，已知的高 GC 区域存在于所有沙鼠中，其特征是所有突变类别的替代率都很高（AT 到 GC、GC 到 AT 和 GC 保守），无论是在同义还是非同义位点。AT 到 GC 的比率高于 GC 到 AT 的比率与高 GC 含量一致。此外，我们在沙鼠中发现了 300 多个已知区域以外的基因，它们的同义 AT 到 GC 替代率异常高。其中，超过 30%的基因组织成至少 17 个可在兆碱基尺度上观察到的大簇。异常的 GC 倾斜取代模式表明在沙鼠谱系中基因组区域的重组率非常高，这可能导致 GC 含量的失控增加。我们的结果表明，GC 含量的快速进化在哺乳动物中是可能的，沙鼠物种为研究 gBGC 的机制提供了一个强大的模型。
