Characterization of gene structure and expression of two toll-like receptors from Japanese flounder, Paralichthys olivaceus.

We cloned the cDNAs and genes of two different types of toll-like receptors from Japanese flounder. The results of homology searches suggested that these genes (designated JF-TLR2 and JF-TLR22) are homologues of human TLR2 and fugu TLR22, respectively. The cDNAs of JF-TLR2 and JF-TLR22 encoded 818 and 961 amino acid residues, respectively. JF-TLR2 and JF-TLR22 contained two distinct structural/functional motifs of the TLR family, such as a leucine-rich repeat (LRR) domain in the extracellular portion and a toll/interleukin-1 receptor (TIR) domain in the intracellular portion. The genes of JF-TLR2 and JF-TLR22 consisted of 12 exons (4.9 kb in total length) and four exons (4.3 kb in total length), respectively. The first exon of each gene is a non-coding exon. Southern blot hybridization indicated that both JF-TLR2 and JF-TLR22 exist as single copies in the genome. These genes were mainly expressed in peripheral blood leukocytes (PBLs) and weakly expressed in PBL-rich organs such as kidney, spleen and gill. Expression of these genes was induced by both peptidoglycan and polyI:C, although the number of JF-TLR-expressing cells were not changed after induction. All of these results suggest that they are involved in the innate immune system.