近日，在中国科学院北京基因组研究所副所长、中国科学院基因组科学与信息重点实验室主任于军研究员的指导下，该重点实验室博士生王大鹏通过对人类千人基因组计划数据的比较分析，进一步证实了两种DNA组分特殊效应在人类基因组中的存在，使该研究组延续十几年的小内含子基本功能和进化机制研究获新进展。相关学术论文在PLoS ONE杂志发表，并且被GenomeWeb网站推荐为“每日精选”。
内含子是真核基因组的重要和必需组成部分，并且它在mRNA的加工、选择性剪接和核外运输等过程中发挥着精确且复杂的作用。在基因组进化研究中，尽管内含子并没有像编码区域一样受到足够的重视，但越来越多证据表明内含子和它们的序列受到潜在功能相关的自然选择作用。
此次博士生王大鹏等的发现：出现在长度范围为88-124nt上的小内含子的删除/插入比值要高于50-86nt；另外，出现在GC含量（鸟嘌呤和胞嘧啶所占的比例）小于65%的小内含子上的删除/插入比值要高于GC含量大于65%的。进一步发现，这两种效应可以在某种程度上得以区分但是并不能完全独立存在。这可能是因为一些GC富集的小内含子在长度上受到较弱的纯化选择，而在GC含量方面受到了较强的正选择。
该研究结果表明，在不同人类群体中，小内含子的长度和GC含量都受到某种自然选择（适应性选择或者负选择）的作用而保持在最适值附近。这些结果为“突变力”模型提供了证据：偏离最适合长度值的小内含子更容易发生插入删除突变。区别于在果蝇中发现的“选择力”模型，该研究揭示了脊椎动物这一分支中小内含子的进化动力学特性，强调了小内含子的潜在的功能重要性，为后续的各物种小内含子功能研究的实验和生物信息研究奠定了理论基础。（生物谷Bioon.com）
生物谷推荐原文出处：
PLoS ONE 6(3): e17945. doi:10.1371/journal.pone.0017945
Both Size and GC-Content of Minimal Introns Are Selected in Human Populations
Dapeng Wang1,2, Jun Yu1*
Background
We previously have studied the insertion and deletion polymorphism by sequencing no more than one hundred introns in a mixed human population and found that the minimal introns tended to maintain length at an optimal size. Here we analyzed re-sequenced 179 individual genomes (from African, European, and Asian populations) from the data released by the 1000 Genome Project to study the size dynamics of minimal introns.
Principal Findings
We not only confirmed that minimal introns in human populations are selected but also found two major effects in minimal intron evolution: (i) Size-effect: minimal introns longer than an optimal size (87 nt) tend to have a higher ratio of deletion to insertion than those that are shorter than the optimal size; (ii) GC-effect: minimal introns with lower GC content tend to be more frequently deleted than those with higher GC content. The GC-effect results in a higher GC content in minimal introns than their flanking exons as opposed to larger introns (≥125 nt) that always have a lower GC content than that of their flanking exons. We also observed that the two effects are distinguishable but not completely separable within and between populations.
Conclusions
We validated the unique mutation dynamics of minimal introns in keeping their near-optimal size and GC content, and our observations suggest potentially important functions of human minimal introns in transcript processing and gene regulation.
