Adaptive evolution of Toll-like receptor 5 in domesticated mammals
1 School of Veterinary Medicine and Science, University of Nottingham, Sutton Bonington LE12 5RD, UK
2 The Roslin Institute and Royal Dick School of Veterinary Studies, The University of Edinburgh, Easter Bush, Midlothian, EH25 9RG, UK
3 Royal Veterinary College, University of London, Hawkshead Lane, Hatfield, Herts, AL9 7TA, UK
4 Moredun Research Institute, Pentlands Science Park, Bush Loan, Penicuik, Midlothian, EH26 0PZ, UK
BMC Evolutionary Biology 2012, 12:122 doi:10.1186/1471-2148-12-122Published: 24 July 2012
Previous studies have proposed that mammalian toll like receptors (TLRs) have evolved under diversifying selection due to their role in pathogen detection. To determine if this is the case, we examined the extent of adaptive evolution in the TLR5 gene in both individual species and defined clades of the mammalia.
In support of previous studies, we find evidence of adaptive evolution of mammalian TLR5. However, we also show that TLR5 genes of domestic livestock have a concentration of single nucleotide polymorphisms suggesting a specific signature of adaptation. Using codon models of evolution we have identified a concentration of rapidly evolving codons within the TLR5 extracellular domain a site of interaction between host and the bacterial surface protein flagellin.
The results suggest that interactions between pathogen and host may be driving adaptive change in TLR5 by competition between species. In support of this, we have identified single nucleotide polymorphisms (SNP) in sheep and cattle TLR5 genes that are co-localised and co-incident with the predicted adaptive codons suggesting that adaptation in this region of the TLR5 gene is on-going in domestic species.