Abrusán György, Giordano Joti, Warburton Peter E
Department of Genetics and Genomic Sciences, Mount Sinai School of Medicine of New York University, Icahn Medical Institute, New York, New York, United States of America.
PLoS Genet. 2008 Aug 29;4(8):e1000172. doi: 10.1371/journal.pgen.1000172.
It has been hypothesised that the massive accumulation of L1 transposable elements on the X chromosome is due to their function in X inactivation, and that the accumulation of Alu elements near genes is adaptive. We tested the possible selective advantage of these two transposable element (TE) families with a novel method, interruption analysis. In mammalian genomes, a large number of TEs interrupt other TEs due to the high overall abundance and age of repeats, and these interruptions can be used to test whether TEs are selectively neutral. Interruptions of TEs, which are beneficial for the host, are expected to be deleterious and underrepresented compared with neutral ones. We found that L1 elements in the regions of the X chromosome that contain the majority of the inactivated genes are significantly less frequently interrupted than on the autosomes, while L1s near genes that escape inactivation are interrupted with higher frequency, supporting the hypothesis that L1s on the X chromosome play a role in its inactivation. In addition, we show that TEs are less frequently interrupted in introns than in intergenic regions, probably due to selection against the expansion of introns, but the insertion pattern of Alus is comparable to other repeats.
据推测，X染色体上L1转座元件的大量积累是由于它们在X染色体失活中发挥的作用，而基因附近Alu元件的积累具有适应性。我们用一种新方法——中断分析，测试了这两个转座元件（TE）家族可能具有的选择优势。在哺乳动物基因组中，由于重复序列的总体丰度高且存在时间久，大量的TE会中断其他TE，这些中断可用于测试TE是否为选择性中性。与中性中断相比，对宿主有益的TE中断预计是有害的且数量较少。我们发现，在包含大多数失活基因的X染色体区域中的L1元件被中断的频率明显低于常染色体，而逃避失活的基因附近的L1元件被中断的频率更高，这支持了X染色体上的L1元件在其失活中起作用的假设。此外，我们表明，TE在内含子中被中断的频率低于基因间区域，这可能是由于对内含子扩张的选择，但Alu元件的插入模式与其他重复序列相当。
