Identification of Avian Toll-Like Receptor 3 and 7 and Analysis of Gene Variation Sites

ABSTRACT Toll-like receptors 3 and 7 (TLR3 and 7) mediate immune responses through the recognition of viral single-stranded RNA and double-stranded RNA and therefore play important roles in host defense. Differences in TLR3 or 7 may affect host resistance to RNA viral infection. To illuminate these differences, the partial coding sequence (CDS) of TLR3 and 7 genes were cloned and amplified from the Phasianus colchicus and Numida meleagris, total 64 avian species of TLR3 and 7 sequences were later analyzed. Based on the results, 315 non-synonymous mutation sites and 202 synonymous mutation sites were also observed in the avian TLR3, and 227 non-synonymous mutation sites and 174 synonymous mutation sites were observed in the avian TLR7. Among these sites, 44 and 45 sites were observed in functional regions of TLR3 and 7, used common variation of amino acids in most avian species. A number of these different sites appeared to affect the recognition and were also visualized. H59Y, E60K, G64R, E93K, L112S, K117E, N118K, R120H, V123M, L163F, R443Q, R459K, E460D, C485H, and F511L for TLR3, and I432V, M437V, and T732S for TLR7 were considered. It is possible that these sites bind to ligands and play crucial roles in viral recognition. These data indicated that the positive selection has occurred in the avian TLR3 and 7 genes.

摘要：Toll样受体3和7（Toll-like receptors 3 and 7，TLR3、TLR7）通过识别病毒单链RNA与双链RNA介导免疫应答，因此在宿主防御过程中发挥重要作用。TLR3或TLR7的基因差异可能影响宿主对RNA病毒感染的抗性。为阐明此类差异，研究人员从环颈雉（Phasianus colchicus）和珠鸡（Numida meleagris）中克隆并扩增了TLR3和TLR7基因的部分编码序列（coding sequence，CDS），后续共分析了64条禽类TLR3和TLR7序列。基于分析结果，在禽类TLR3中共发现315个非同义突变位点与202个同义突变位点，在禽类TLR7中则发现227个非同义突变位点与174个同义突变位点。其中，分别有44个和45个位点位于TLR3和TLR7的功能区域，且在多数禽类物种中呈现氨基酸共同变异特征。此类差异位点中有多个似乎会影响配体识别功能，且已被可视化分析。针对TLR3的H59Y、E60K、G64R、E93K、L112S、K117E、N118K、R120H、V123M、L163F、R443Q、R459K、E460D、C485H及F511L，以及针对TLR7的I432V、M437V与T732S均被纳入研究考量。上述位点或可参与配体结合，并在病毒识别过程中发挥关键作用。本研究数据表明，禽类TLR3和TLR7基因曾经历正向选择作用。