White Stephen N, Taylor Kristen H, Abbey Colette A, Gill Clare A, Womack James E
Department of Veterinary Pathobiology and Animal Science, Texas A&M University, College Station, TX 77843, USA.
Proc Natl Acad Sci U S A. 2003 Sep 2;100(18):10364-9. doi: 10.1073/pnas.1333957100. Epub 2003 Aug 12.
Toll-like receptor 4 (TLR4) is a cell-surface receptor that activates innate and adaptive immune responses. Because it recognizes a broad class of pathogen-associated molecular patterns presented by lipopolysaccharides and lipoteichoic acid, TLR4 is a candidate gene for resistance to a large number of diseases. In particular, mouse models suggest TLR4 as a candidate gene for resistance to major agents in bovine respiratory disease and Johne's disease. The coding sequence of bovine TLR4 is divided into three exons, with intron/exon boundaries and intron sizes similar to those of human TLR4 transcript variant 1. We amplified each exon in 40 individuals from 11 breeds and screened the sequence for single-nucleotide polymorphisms (SNPs). We identified 32 SNPs, 28 of which are in the coding sequence, for an average of one SNP per 90 bp of coding sequence. Eight SNPs were nonsynonymous and potentially alter specificity of pathogen recognition or efficiency of signaling. To evaluate the functional importance of these SNPs, we used codon-substitution models to detect diversifying selection in an extracellular region that may physically interact with ligands. One nonsynonymous SNP is located within this region, and other substitutions are in adjacent regions that may interact with coreceptor molecules. The 32 SNPs were found in 20 haplotypes that can be assigned to geographic ranges of origin. Haplotype-tagging SNP analysis indicated that 12 SNPs need to be genotyped to distinguish these 20 haplotypes. These data provide a basic understanding of bovine TLR4 sequence variation and supply haplotype markers for disease association studies.
Toll样受体4（TLR4）是一种激活先天性和适应性免疫反应的细胞表面受体。由于它能识别脂多糖和脂磷壁酸所呈现的一大类病原体相关分子模式，TLR4是对多种疾病具有抗性的候选基因。特别是，小鼠模型表明TLR4是抵抗牛呼吸道疾病和副结核的主要病原体的候选基因。牛TLR4的编码序列分为三个外显子，其内含子/外显子边界和内含子大小与人类TLR4转录变体1相似。我们扩增了11个品种40个个体的每个外显子，并筛选序列中的单核苷酸多态性（SNP）。我们鉴定出32个SNP，其中28个位于编码序列中，平均每90个编码序列碱基中有一个SNP。8个SNP是非同义的，可能会改变病原体识别的特异性或信号传导效率。为了评估这些SNP的功能重要性，我们使用密码子替换模型来检测在可能与配体发生物理相互作用的细胞外区域中的多样化选择。一个非同义SNP位于该区域内，其他替换位于可能与共受体分子相互作用的相邻区域。这32个SNP存在于20种单倍型中，这些单倍型可根据起源的地理范围进行分类。单倍型标签SNP分析表明，需要对12个SNP进行基因分型以区分这20种单倍型。这些数据为牛TLR4序列变异提供了基本认识，并为疾病关联研究提供了单倍型标记。
