Patterns of insertion and deletion in contrasting chromatin domains
Patterns of insertion and deletion in contrasting chromatin domains
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DOI：
10.1093/oxfordjournals.molbev.a004045
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发表时间：
2002-12-01
影响因子：
10.7
通讯作者：
Lozovsky, ER
中科院分区：
文献类型：
--
作者：
Blumenstiel, JP;Hartl, DL;Lozovsky, ER
转座元件(TES)在基因组进化中起着重要的作用。在果蝇中，它们不成比例地出现在低重组的区域，如异染色质。这种模式被归因于对正常重组区域中重复元件的选择，这是由于(1)TE插入在基因附近或基因内的轻微有害位置效应，或(2)对TE重复之间的异位交换引起的染色体异常的强烈选择。为了估计染色质不同成分中的自发缺失率，我们使用了有缺陷的非长端重复序列(LTR)TE，这些TE是“到达即死”(DOA)，并且不能转座。这些元素之前已经提供了证据，证明与哺乳动物相比，果蝇的自发缺失率极高，这至少可能解释了这些生物基因组大小的差异的部分原因。然而，由于对异位交换可能性较小的阳性选择，缺失率可能被高估。在这篇文章中，我们发现，在异染色质和常染色质重组低的区域，DOA重复序列的自发缺失率与常染色质重组正常的区域一样高。我们还研究了五个非LTR家族在整个基因组中的年龄分布。我们发现，这些TES的转位历史模式有很大的变化。TES在异染色质中的过度表达主要是由于它们在异染色质中的保留时间较长，从插入到异染色质的平均时间可以证明这一点。最近插入的片段在基因组中的分布要均匀得多。这一对比表明，TES在异染色质和低重组的等染色质区域的聚集不是由于偏向的转位，而是由于相对于正常重组区域，这些区域有更大的固定概率。
Transposable elements (TEs) play a fundamental role in the evolution of genomes. In Drosophila they are disproportionately represented in regions of low recombination, such as in heterochromatin. This pattern has been attributed to selection against repeated elements in regions of normal recombination, owing to either (1) the slightly deleterious position effects of TE insertions near or into genes, or (2) strong selection against chromosomal abnormalities arising from ectopic exchange between TE repeats. We have used defective non-long-terminal repeat (LTR) TEs that are "dead-on-arrival" (DOA) and unable to transpose in order to estimate spontaneous deletion rates in different constituents of chromatin. These elements have previously provided evidence for an extremely high rate of spontaneous deletion in Drosophila as compared with mammals, potentially explaining at least part of the differences in the genome sizes in these organisms. However, rates of deletion could be overestimated due to positive selection for a smaller likelihood of ectopic exchange. In this article, we show that rates of spontaneous deletion in DOA repeats are as high in heterochromatin and regions of euchromatin with low recombination as they are in regions of euchromatin with normal recombination. We have also examined the age distribution of five non-LTR families throughout the genome. We show that there is substantial variation in the historical pattern of transposition of these TEs. The overrepresentation of TEs in the heterochromatin is primarily due to their longer retention time in heterochromatin, as evidenced by the average time since insertion. Fragments inserted recently are much more evenly distributed in the genome. This contrast demonstrates that the accumulation of TEs in heterochromatin and in euchromatic regions of low recombination is not due to biased transposition but by greater probabilities of fixation in these regions relative to regions of normal recombination.