Episodic positive selection in the evolution of avian toll-like receptor innate immunity genes.
Episodic positive selection in the evolution of avian toll-like receptor innate immunity genes.
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DOI：
10.1371/journal.pone.0089632
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发表时间：
2014
期刊：
影响因子：
3.7
通讯作者：
Jamieson IG
中科院分区：
文献类型：
--
作者：
Grueber CE;Wallis GP;Jamieson IG
Toll样受体（TLR）是一个保守的模式识别分子家族，负责启动先天性和获得性免疫反应。由于它们在宿主防御中起着关键作用，这些基因在进化和群体遗传学文献中受到越来越多的关注，因为它们的变异代表了适应性进化的潜在目标。然而，病原体介导的选择（即偶发性正选择）在这些基因的进化中的作用仍然知之甚少，并且尚未在哺乳动物之外进行研究。最近增加的鸟类TLR序列的数量，使我们能够检查的选择过程，影响了10个已知的鸟类TLR基因的进化。具体来说，我们测试了偶发性正选择，以确定在其进化的大部分时间里经历纯化选择的密码子，其中穿插着可能仅发生在有限谱系中的正选择爆发。我们包括多达23个物种的基因（平均值= 16.0），并观察到，虽然纯化选择是显而易见的，平均4.5%的密码子经历了情节积极的选择在所有的基因座。 对于四个基因，其中的序列覆盖率穿越细胞外富含亮氨酸的重复区（LRR）和跨膜/细胞内结构域的蛋白质，增加正选择观察到在细胞外结构域，与理论预测一致。我们的研究结果提供的证据表明，情节积极的选择发挥了重要作用，在大多数鸟类TLR的进化，与这些位点的病原体识别和宿主-病原体协同进化的机制的作用是一致的。
Toll-like receptors (TLRs) are a family of conserved pattern-recognition molecules responsible for initiating innate and acquired immune responses. Because they play a key role in host defence, these genes have received increasing interest in the evolutionary and population genetics literature, as their variation represents a potential target of adaptive evolution. However, the role of pathogen-mediated selection (i.e. episodic positive selection) in the evolution of these genes remains poorly known and has not been examined outside of mammals. A recent increase in the number of bird species for which TLR sequences are available has enabled us to examine the selective processes that have influenced evolution of the 10 known avian TLR genes. Specifically, we tested for episodic positive selection to identify codons that experience purifying selection for the majority of their evolution, interspersed with bursts of positive selection that may occur only in restricted lineages. We included up to 23 species per gene (mean = 16.0) and observed that, although purifying selection was evident, an average of 4.5% of codons experienced episodic positive selection across all loci. For four genes in which sequence coverage traversed both the extracellular leucine-rich repeat region (LRR) and transmembrane/intracellular domains of the proteins, increased positive selection was observed at the extracellular domain, consistent with theoretical predictions. Our results provide evidence that episodic positive selection has played an important role in the evolution of most avian TLRs, consistent with the role of these loci in pathogen recognition and a mechanism of host-pathogen coevolution.
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