Genome-wide identification and characterization of toll-like receptor 5 () in fishes.

Toll-like receptors 5 (TLR5), a member of the toll-like receptors (TLRs) family, is a class of pattern recognition receptors (PRRs) that recognize pathogen-associated molecular patterns (PAMPs). It responds to vertebrate recognition of bacterial flagellin and participates in innate immune responses. However, genome-wide identification and characterization of TLR5 in fishes have not been investigated. Here, three TLR5M isotypes (, , and ) and a TLR5S are all extracted from fish genomes on the basis of phylogenetic and synteny analyses. We confirmed that the non-teleost fishes have one gene, as well as additional genes ( and ) in teleost fishes. In addition, some special teleost fishes possess two to three genes, which have undergone the fourth whole-genome duplication (WGD). According to our results, we inferred that the diversity of genes in fishes seems to be the result of combinations of WGD and gene loss. Furthermore, isoforms displayed differences at the flagellin interaction sites and viral binding sites, and showed lineage-specific, which indicated that duplicates may generate functional divergence. Bacterial experiments also supported the idea that and are subfunctionalized to sense bacterial flagellin. In summary, our present comparative genomic survey will benefit for further functional investigations of genes in fish.