Groth Sam B, Blumenstiel Justin P
From the Department of Ecology and Evolutionary Biology, University of Kansas, 1200 Sunnyside Avenue, Lawrence, KS 66049 (Groth and Blumenstiel).
J Hered. 2017 Jan;108(1):36-44. doi: 10.1093/jhered/esw050. Epub 2016 Aug 24.
Genomes are comprised of contrasting domains of euchromatin and heterochromatin, and transposable elements (TEs) play an important role in defining these genomic regions. Therefore, understanding the forces that control TE abundance can help us understand the chromatin landscape of the genome. What determines the burden of TEs in populations? Some have proposed that drift plays a determining role. In small populations, mildly deleterious TE insertion alleles are allowed to fix, leading to increased copy number. However, it is not clear how the rate of exposure to new TE families, via horizontal transfer (HT), can contribute to broader patterns of genomic TE abundance. Here, using simulation and analytical approaches, we show that when the effects of drift are weak, exposure rate to new TE families via HT can be an important determinant of genomic copy number. If population exposure rate is proportional to population size, larger populations are expected to have a higher rate of exposure to rare HT events. This leads to the counterintuitive prediction that larger populations may carry a higher TE load. We also find that increased rates of recombination can lead to greater probabilities of TE establishment. This work has implications for our understanding of the evolution of chromatin landscapes, genome defense by RNA silencing, and recombination rates.
基因组由常染色质和异染色质的不同结构域组成，转座元件（TEs）在界定这些基因组区域中发挥着重要作用。因此，了解控制TE丰度的因素有助于我们理解基因组的染色质格局。是什么决定了群体中TE的负担？有人提出，遗传漂变起决定性作用。在小群体中，轻度有害的TE插入等位基因得以固定，导致拷贝数增加。然而，尚不清楚通过水平转移（HT）接触新TE家族的速率如何影响基因组TE丰度的更广泛模式。在此，我们使用模拟和分析方法表明，当遗传漂变的影响较弱时，通过HT接触新TE家族的速率可能是基因组拷贝数的重要决定因素。如果群体接触速率与群体大小成正比，那么较大的群体预计接触罕见HT事件的速率更高。这导致了一个与直觉相反的预测，即较大的群体可能携带更高的TE负荷。我们还发现，重组率的提高会导致TE建立的可能性更大。这项工作对我们理解染色质格局的进化、RNA沉默介导的基因组防御以及重组率具有重要意义。
