Characterization, Expression And Evolution Analysis Of Toll-Like Receptor 1 Gene In Pufferfish (Tetraodon Nigroviridis)

The Toll-like receptor (TLR) family is a pathogen-associated molecular pattern recognition receptor family that plays key roles in the activation of innate immune system. As an important member of TLRs, TLR1 is involved in the recognition of triacylated lipoproteins and mycobacterial products by binding to TLR2 to form a heterodimer. Although partial sequences of TLR1 has been predicted in Fugu and Danio by bioinformatics, the molecular cloning and characterization of this gene in fish still remains largely unclear. Here we report the full-length sequence of TLR1 gene in the pufferfish (Tetraodon nigroviridis), providing experimental evidence to its existence in fish. The cloned Tetraodon TLR1 (TnTLR1) cDNA exhibited 2587 bp in length and contains a 122-bp 5' untranslated region (UTR), a 2391-bp open reading frame and a 74-bp 3' UTR. Expression of TLR1 transcripts in most selected tissues were detected at lower levels; however, the transcripts in spleen was markedly increased (threefold) after stimulation with lipopolysaccharide, indicating that TLR1 in fish may be involved in the inflammatory responses to bacterial endotoxin or Gram-negative bacteria infection. Gene organization of TnTLR1 is similar to mammalian and avian, and a high degree of conservation of chromosome synteny exists between them. The protein sequence shares 33.7-77.3% identity with known TLR1 members. Phylogenetic analysis grouped TnTLR1 with other fish TLRs on a separated branch, excluded from mammalian and avian TLR1s. TnTLR1 with 796 amino acids has a calculated molecular mass of 90.69 kDa and a theoretical pI of 8.43. Structurally, TnTLR1 has a Toll/interleukin-1 receptor (TIR) domain, a transmembrane domain and leucine-rich repeat domain which are the hallmarks of TLR family. Phylogenetic analysis provided evidence that the TnTLR1 was very close to mammalian TLR1, TLR6 and TLR10 and seemed to be their common ancestor. This report of the full-length TLR1 gene in Tetraodon will provide us further insights into the study of both function and evolution of fish TLRs as a whole.