Molecular cloning and expression analysis of toll-like receptor genes (TLR7, TLR8 and TLR9) of golden pompano (Trachinotus ovatus)

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Toll like receptor (TLR) 7, 8 and 9 are intracellular TLRs which play important roles in host immune defense against bacterial or virus pathogens. In this study, TLR7, 8 and 9 were identified from golden pompano (Trachinotus ovatus), a marine teleost with great economic values. Sequence analysis revealed that the three TLRs contained several conserved characteristic features, including signal peptides, 25 leucine-rich repeat (LRR) motifs, a transmembrane domain and a TIR motif. These three TLRs shared high sequence identity and similarity with their counterparts from other teleosts. The phylogenetic tree analysis showed the three TLRs were clustered well with their piscine counterparts, confirming the correctness of their nomenclatures and closed relationships during evolution. Quantitative real-time PCR revealed that the three TLRs were ubiquitously expressed in all the tested tissues from normal pompano, with high expression in spleen and head kidney, indicating their role in immune reaction. Further, pompano TLR7 and TLR8 was up-regulated in spleen and head kidney from 12 h to 48 h following polyI:C challenge, but remained no changes to Vibrio alginilyticus infection. In contrast, pompano TLR9 could be induced by V. alginilyticus infection but remained apathetic to polyI:C challenge. These results indicated that pompano TLR7, 8 and 9 might have distinct roles in response to bacterial or virus pathogens. Our results provided the basis for further study on ligand specificity and signaling pathways of fish TLRs which are required for elucidating the immune functions of fish TLRs.

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