Evolution of the chicken Toll-like receptor gene family: a story of gene gain and gene loss.
BACKGROUND
Toll-like receptors (TLRs) perform a vital role in disease resistance through their recognition of pathogen associated molecular patterns (PAMPs). Recent advances in genomics allow comparison of TLR genes within and between many species. This study takes advantage of the recently sequenced chicken genome to determine the complete chicken TLR repertoire and place it in context of vertebrate genomic evolution.


RESULTS
The chicken TLR repertoire consists of ten genes. Phylogenetic analyses show that six of these genes have orthologs in mammals and fish, while one is only shared by fish and three appear to be unique to birds. Furthermore the phylogeny shows that TLR1-like genes arose independently in fish, birds and mammals from an ancestral gene also shared by TLR6 and TLR10. All other TLRs were already present prior to the divergence of major vertebrate lineages 550 Mya (million years ago) and have since been lost in certain lineages. Phylogenetic analysis shows the absence of TLRs 8 and 9 in chicken to be the result of gene loss. The notable exception to the tendency of gene loss in TLR evolution is found in chicken TLRs 1 and 2, each of which underwent gene duplication about 147 and 65 Mya, respectively.


CONCLUSIONS
Comparative phylogenetic analysis of vertebrate TLR genes provides insight into their patterns and processes of gene evolution, with examples of both gene gain and gene loss. In addition, these comparisons clarify the nomenclature of TLR genes in vertebrates.
Temperley
Nicholas D
ND
Department of Genomics and Genetics, Roslin Institute (Edinburgh), Roslin, Midlothian EH25 9PS, UK. nick.temperley@bbsrc.ac.uk
Berlin
Sofia
S
Paton
Ian R
IR
Griffin
Darren K
DK
Burt
David W
DW
D000818:Animals; D030161:Avian Proteins / Q000737:chemistry / Q000235:genetics; D002645:Chickens / Q000235:genetics*; D020451:Contig Mapping; D019143:Evolution, Molecular; D006801:Humans; D051379:Mice; D005810:Multigene Family / Q000235:genetics*; D010802:Phylogeny; D017434:Protein Structure, Tertiary; D051381:Rats; D012680:Sensitivity and Specificity; D017386:Sequence Homology, Amino Acid; D009626:Terminology as Topic; D051193:Toll-Like Receptors / Q000737:chemistry / Q000235:genetics*
D030161:Avian Proteins; D051193:Toll-Like Receptors