Two non-mammalian toll-like receptors (TLR21 and TLR22) from golden pompano (Trachinotus ovatus): Molecular cloning, gene characterization and expression analysis

Toll-like receptors (TLRs), important pattern recognition receptors (PRRs), involve in recognizing pathogen-associated molecular patterns (PAMPs) and play crucial roles in the host innate immunity. In the present study, two non-mammalian TLRs, troTLR21 and troTLR22, were identified and characterized from golden pompano (Trachinotus ovatus), a marine teleost with great economic values. The two TLRs were typical TLRs, containing several motifs conserved in TLRs family including leucine-rich repeat (LRR) motifs, a transmembrane domain, and a toll/interleukin-1 receptor (TIR) domain. The two TLRs shared high sequence identity with their counterparts in other teleosts. Phylogenetic tree analysis showed that troTLR21 and troTLR22 were well clustered with other fish TLR21 and TLR22, respectively. Quantitative real-time PCR (qPCR) revealed that the two TLRs were ubiquitously expressed in all investigated tissues, with higher transcription levels in the immune-related tissues (spleen and head kidney (HK)). Further, the expressions of troTLR21 and troTLR22 were significantly up-regulated in HK and spleen following Vibrio alginolyticus, lipopolysaccharide (LPS), and polyinosinic: polycytidylic acid (polyI:C) stimulation. Our results suggested that the two TLRs involve in the immune response against pathogen invasion in golden pompano, providing solid basis for further study the functions of fish-specific TLRs.