Molecular Characterization of Coding Sequence and mRNA Expression Pattern of Toll-like Receptor 15 in Japanese Quail (Coturnix japonica) and Indigenous Chicken Breeds (Aseel and Kadaknath)

Toll-like receptors (TLRs) play a crucial role in innate immune response of mammalian and avian species. The chicken TLR repertoire consists of ten genes. TLR15 is avian specific TLR with no mammalian homologue. The present study has characterized full-length coding sequence of TLR15 in Japanese quail and Indian indigenous chicken (Aseel and Kadaknath). Open reading frame of all three sequences were 2,607 bp long encoding 868 amino acids similar to that of broiler chicken. Japanese quail, Aseel and Kadaknath sequences showed 95.1%, 99.7% and 99.8% similarity with broiler chicken TLR15 sequence at nucleotide level respectively. Domain architecture analysis revealed minor variations in number and position of leucine rich repeats (LRRs) in the ectodomain region of all three sequences. Phylogenetic analysis revealed TLR15 groups with high bootstrap support to avian TLR1 family members. TLR15 mRNA expression in a range of tissues as quantified by real time PCR was found significantly (P<0.01) higher in Aseel in comparison to Kadaknath and Japanese quail in most of the tissues investigated.