title: Identification and sequence analysis of chicken Toll-like receptors.
abstract: Toll-like receptors (TLRs) play an important role in the recognition of microbial components. Only chicken TLR2 and -4 have been reported in the literature. The objectives of this study were to identify new chicken TLRs and to evaluate evolutionary significance of these receptors. Searching chicken genomic databases and DNA sequencing revealed five new TLRs, TLR1 (type 1 and 2), -3, -5, and -7. No chicken orthologues of mammalian TLR8, -9, or -10 were found. As in mammals, all chicken TLRs (chTLRs) share identical protein secondary structure that consists of several leucine-rich domains, a transmembrane domain, and Toll/Interleukin-1 receptor domain(s). Phylogenetic analyses indicate that the identified chTLR genes are the orthologues of TLRs in mammals. Analyses of the number of synonymous substitutions per synonymous site and nonsynonymous substitutions per nonsynonymous site indicate that the nucleotide sequences coding for the leucine-rich repeats of chicken TLR1 type 1 and type 2 were significantly under positive Darwinian selection. In contrast, the sequences of other TLRs were under purifying selection. These results support the hypothesis that one of the major evolutionary strategies of the innate immune system is to recognize a few highly conserved microbial components with several conserved TLRs. The results also indicate that the sequence changes in the ligand-binding domains of TLR1 in chickens provide adaptive advantages during evolution.
authors.affiliation: Department of Poultry Science, Texas A&M University, College Station, TX, 77843, USA.
authors.forename: Ahmet
authors.initials: A
authors.lastname: Yilmaz
authors.forename: Shixue
authors.initials: S
authors.lastname: Shen
authors.forename: David L
authors.initials: DL
authors.lastname: Adelson
authors.forename: Suresh
authors.initials: S
authors.lastname: Xavier
authors.forename: James J
authors.initials: JJ
authors.lastname: Zhu
mesh_terms: D000595:Amino Acid Sequence; D000818:Animals; D002645:Chickens / Q000276:immunology*; D002874:Chromosome Mapping; D020869:Gene Expression Profiling; D000090263:Leucine-Rich Repeat Proteins; D008562:Membrane Glycoproteins / Q000032:analysis* / Q000737:chemistry / Q000235:genetics; D008969:Molecular Sequence Data; D010802:Phylogeny; D011506:Proteins / Q000032:analysis / Q000737:chemistry / Q000235:genetics; D011956:Receptors, Cell Surface / Q000032:analysis* / Q000737:chemistry / Q000235:genetics; D051194:Toll-Like Receptor 1; D051195:Toll-Like Receptor 2; D051200:Toll-Like Receptor 8; D051193:Toll-Like Receptors
chemical_list: D000090263:Leucine-Rich Repeat Proteins; D008562:Membrane Glycoproteins; D011506:Proteins; D011956:Receptors, Cell Surface; D051194:Toll-Like Receptor 1; D051195:Toll-Like Receptor 2; D051200:Toll-Like Receptor 8; D051193:Toll-Like Receptors