In chicken, TLR1 and 2 genes are individually duplicated to encode four different proteins of the TLR2 subfamily:
- chTLR1 type 1 (TLR1-1, or TLR1LA, or TLR16)
- chTLR1 type 2 (TLR1-2 or TLR1LB)
- chTLR2 type 1(TLR2A or TLR2-1)
- chTLR2 type 2 (TLR2B or TLR2-2)
. The TLR1 and TLR2 gene duplication events were estimated to have taken place about 147 and 65 million years ago respectively (Temperley ND et al. 2008).
Analyses of chicken genome revealed that all chTLR2 and chTLR1 isoforms are located on Chromosome 4 and are encoded by one exon, like human TLR2 and TLR1. The phylogenetic comparative analysis also showed that chTLR2 isoforms are two distinct genes (not splicing products of the same gene) and TLR2A and B are both orthologs of the single TLR2 of mammals (Temperley ND et al 2008, Cormican et al 2009). Although chicken TLR1 type 1 and 2 genes were reported by Yilmaz et al. (2004) to be highly similar to human TLR1 and TLR6 genes, further analysis revealed that chicken TLR1 and human TLR1/6/10 are not orthologs (Temperley ND et al 2008).
The functional profile of chicken TLR2 subfamily proteins is similar to human; members of TLR2 subfamily respond to lipoproteins through heterodimer formation.