Molecular characterizations of TLR1 and TLR2 in Qihe crucian carp (Carassius auratus) and responses to stimulations of Aeromonas hydrophila and TLR ligands

Toll-like receptors (TLRs), as the members of pattern-recognition receptors (PRRs), play a crucial role in innate immunity due to its significant function to recognize pathogens and activate downstream elements in signaling pathway. In the present study, the full-length cDNA sequences of TLR1 and TLR2 were cloned in the natural triploid Qihe crucian carp (Carassius auratus). The complete cDNA sequence of TLR1 was 2754 bp which was comprised of 5′ UTR of 60 bp, 3′ UTR of 300 bp, and an open reading frame of 2394 bp encoding 797 amino acids. The full-length cDNA sequence of TLR2 was 2605 bp, containing 5′ UTR of 36 bp, 3′ UTR of 202 bp, and an open reading frame of 2367 bp, encoding 788 amino acids. The mRNA expressions of CaTLR1 and CaTLR2 were detected to be constitutive at various embryonic developmental stages, and it was indicated that the similar expression pattern that mRNA expression levels were high at early development, then went down, and increased at later development stage. With regard to mRNA expression levels of CaTLR1 and CaTLR2 in various tissues of Qihe crucian carp, it showed to be constitutive with being higher in the liver and heart and the lowest in ovary. The mRNA expressions of CaTLR1 and CaTLR2 were profiled by quantitative real-time PCR following intraperitoneal injections of Aeromonas hydrophila and TLR ligands including LPS, PGN, and PolyI:C. Compared with the control, both CaTLR1 and CaTLR2 expressions were upregulated in most tissues of fish after challenges of LPS, PGN, PolyI:C, or A. hydrophila, although expression patterns varied in different tissues (gill, liver, spleen, trunk kidney, and head kidney). Together, these data highlighted the important role of CaTLR1 and CaTLR2 in recognizing LPS, PGN, PolyI:C, and A. hydrophila and in augmenting the innate immune ability against bacterial and viral infections in Qihe crucian carp.