Cloning and sequence analysis of chicken toll like receptor-7 expressed sequence tag

Toll like receptors (TLRs) are the most important Pattern Recognition Receptors (PRRs) that recognize conserved microbial signature molecules, Pathogen Associated Molecular Patterns(PAMPS). TLR7 recognizes viral genomic single stranded (ss) RNA and its role in antiviral immunity is not completely established. A 414 bp fragment of Toll Like receptor 7 Leucine Rich Repeat(LRR) Expressed Sequence Tag(EST) was amplified, cloned, sequenced (Accession no. FJ908712) and characterized in chickens. The deduced protein showed 70% identity with Anas platyrhynchus and 60% identity with Bos taurus, Bos indicus, Bison, Bubalus bubalis, Canis familiaris, Danio rerio, Equus caballus, Felis cattus, Gorilla gorilla and Homo sapiens TLR 7 protein sequences. On phylogenetic analysis, the neighbor joining tree was with relatively higher bootstrap values providing clear resolution of all the nodes. Gallus gallus sequence clustered away from the mammalian sequences, closest to the primate group (Homo sapiens, Macaca mulatta, Gorilla gorilla), and farthest from bovid group (Bos taurus, Bos indicus, Ovis aries). Analysis of the number of synonymous substitutions per synonymous site and nonsynonymous substitutions per nonsynonymous site indicate that the nucleotide sequences coding for the LRR in TLR7 were significantly under purifying selection and not under positive selection.