The RAG2 gene of yellow catfish (Tachysurus fulvidraco) and its immune response against Edwardsiella ictaluri infection.

Recombination-activating gene 2 (rag 2) allies with recombination-activating gene 1 (rag 1) and regulates the V(D)J recombination of immunoglobulin (Ig) and T-cell receptor (TCR) genes. Being a key player in the adaptive immune response of vertebrates, functional characterization of rag 2 from yellow catfish is beneficial for understanding the biological response towards the pathogens. In this report, we have cloned and characterized the rag 2 gene of yellow catfish, and a particular pattern of expression was analysed in the major tissues of yellow catfish. The results showed that the open reading frame (ORF) of yellow catfish rag 2 was 1596 bp in length, which encodes a peptide of 531 amino acids. The multiple sequence alignment and phylogenetic analysis of rag 2 of yellow catfish with other species showed the conserved regions and the classical taxonomic evolution among the different vertebrate species. The qRT-PCR and Western blot results revealed that rag 2 transcripts and proteins were present in various tissues of yellow catfish with relatively high expression in the tissues of the thymus, head-kidney, and spleen. The systematic distribution analysis of the rag 2 expression by immunohistochemistry (IHC) using the rabbit polyclonal antibody, exposed relatively high expression in head kidney, spleen and thymus tissues after infected with Edwardsiella ictaluri. Moreover, the temporal expression of rag 2 and pro-inflammatory cytokines (IL-1β and TNF-α) were significantly upregulated at different time points in the specific lymphoid tissues of yellow catfish following E. ictaluri infection. Our findings suggest that rag 2 potentially exhibited the immunological response in primary lymphoid tissues of yellow catfish against bacterial infection. This study will provide an essential source about rag 2 gene and its relationship with the inflammatory cytokines during infection.