反刍动物Toll样受体多基因家族的分子进化及表达模式分析

Molecular Evolution and Expression Patterns of a Multigene Family of Toll-like Receptors in Ruminants

为了了解Toll样受体(Toll-like receptors,TLRs)多基因家族在反刍动物中的分子进化关系及表达分析。本研究基于6个科53种反刍动物基因组,利用同源基因对反刍动物TLR 1-10基因进行系统鉴定,分析其染色体定位和基因结构、进化关系、选择压力(ω),并结合转录组数据明晰TLR基因在各组织的表达模式。研究结果表明:1)反刍动物的TLR 1-10均为单拷贝基因,按进化关系分为TLR1(TLR1/6/10)、TLR2、TLR4、TLR3(TLR3/5)、TLR7(TLR 7/8/9)亚家族。2)反刍动物10个TLR基因整体上经受了纯化选择作用(ω<1),但共有35个氨基酸位点受到强烈的正选择作用;牛科比鹿科具有更高的ω值和更高比例的正选择位点,非病毒性TLRs比病毒性TLRs具有更高的ω和更多的正选择位点,提示鹿科TLR以及病毒性的TLR受到较强的进化约束力。3)在绵羊中,10个TLRs基因在免疫组织中均有所表达,其中TLR 2和TLR 9在外周血单个核细胞(PBMC)中存在高度表达。结果提示,反刍动物TLRs基因家族在进化水平上是相对保守的,均受到强烈的纯化选择作用,TLR 2和TLR 9在PBMC组织起主要的免疫作用。

The study aimed to understand the molecular evolutionary relationships and expression analysis of the multigene family of Toll-like receptors(TLRs)in ruminants.The TLR 1-10 genes was systematically identified in ruminants based on the genomes of 53 ruminant species from 6 families,their chromosomal localization and gene structure,evolutionary relationships,selection pressure(ω)was analyzed,and the expression patterns of TLR genes was clarified combined with transcriptomic data in various tissues.The results showed that:1)TLR 1-10 in ruminants were all single-copy genes,which were classified into TLR1(TLR1/6/10),TLR2,TLR4,TLR3(TLR 3/5)and TLR7(TLR 7/8/9)subfamilies according to evolutionary relationships.2)The 10 TLR genes in ruminants as a whole underwent purifying selection(ω<1),but a total of 35 amino acid loci were subject to strong positive selection;bovidae had higherωvalues and a higher proportion of positive selection loci than cervidae,and non-viral TLRs had higherωand more positive selection loci than viral TLRs,suggesting that cervidae TLRs as well as viral TLRs were subject to stronger evolutionary binding.3)In sheep,all 10 TLR genes were expressed in immune tissues,with TLR 2 and TLR 9 expressed at relatively high levels in PBMC.The results suggest that the gene family of ruminant TLRs is relatively conserved at the evolutionary level and both are subject to strong purifying selection,with TLR 2 and TLR 9 playing a major immune role in PBMC tissues.