Cloning and expression analysis of recombination activating genes (RAG1/2) in red snapper (Lutjanus sanguineus)

Recombination activating genes (RAG1 and RAG2), involved in the V(D)J recombination of immunoglobulin and T-cell receptor genes play a crucial role in the adaptive immune response in vertebrates. The expression of these genes was required for the proper development and maturity of lymphocytes so that they can be used as useful markers to evaluate the development of lymphoid organ. In this paper, the cDNA of RAG1 and RAG2 in red snapper, Lutjanus sanguineus were cloned by homological cloning and rapid amplification of cDNA ends (RACE) methods. Results showed the full length of RAG1 cDNA was 3944 bp, containing a 5' untranslated region (UTR) of 200 bp, a 3'-UTR of 561 bp and an open reading frame of 3183 bp encoding 1060 amino acids. Three important structural motifs, a RING/U-box domain, a RING/FYVE/PHD-type domain and a RAG Nonamer-binding domain were detected in the deduced amino acid sequence of RAG1 by InterProScan analysis. The full length of RAG2 cDNA was 2200 bp, consisting of a 141 bp 5'-UTR, a 457 bp 3'-UTR and an open reading frame of 1602 bp encoding 533 amino acids. Two important structural motifs, a Galactose oxidase/kelch, beta-propeller domain and a kelch-type beta-propeller domain were detected in the deduced amino acid sequence of RAG2 by InterProScan analysis. BLAST analysis revealed that the RAG1 and RAG2 in red snapper shared a high homology with other known RAG1 and RAG2 genes, while the greatest degree of identity was observed with Hippoglossus hippoglossus RAG1 at 82% and Takifugu rubripes RAG2 at 87%, respectively. The differential expressions of RAG1 and RAG2 in various tissues of red snapper were analyzed by fluorescent quantitative real-time PCR. The overall expression pattern of the two genes was quite similar. In healthy red snappers, the RAGs transcripts were mainly detected in thymus, following head kidney, spleen, intestine, liver and brain. After vaccinated with inactivated Vibrio alginolyticus 48 h later, the RAGs mRNA expression was significantly up-regulated in all studied tissues of red snapper. A clear time-dependent expression pattern of RAG1 and RAG2 after immunization and the expression reached the highest level at 48 h in thymus, 60 h in head kidney and spleen, respectively. These findings indicated that RAG1 and RAG2 could play an important role in the immune response to bacteria in red snapper.