Abstract:Arginase Ⅱ(Arg-Ⅱ) is a type of arginase. It mainly participates in the urea cycle, and has been found to play an important role in the pathological process. However, its role in fish is not well reported. In this milieu, we obtained the full cDNA of Arg-Ⅱ of Japanese flounder (Paralichthys olivaceus) and detected its space-time expression profile in the immune tissue and bacterial infected tissue of Japanese flounder. The results showed that the Arg-Ⅱ gene consists of 1882 nucleotides, including an open reading frame (1150 bp) that encodes a protein of 349 amino acids (with deduced molecular mass of 38.02 kDa and theoretical isoelectric point of 6.42). The amino acid of Arg-Ⅱ protein in Japanese flounder displayed the typical structure of arginase, therefore we assumed that it might have functions similar to that in mammals. Phylogenetic tree analysis also confirmed that fish Arg-Ⅱ formed a cluster, and Japanese flounder Arg-Ⅱ was most closely related to that of Lates calcarifer (93%). Quantitative real-time PCR (q-RT PCR) analysis showed that the mRNA of Arg-Ⅱ is mainly expressed in immune tissues, such as the liver, spleen, gills, and kidney. Intensive study showed that the mRNA expression of gene Arg-Ⅱ was significantly upregulated after 6~12 h of Edwardsiella tarda challenge, and then returned to normal condition in the immune tissues of Japanese flounder. The expression of Arg-Ⅱ was also significantly upregulated in the in vitro cultured E. tarda challenged Japanese flounder phagocyte. The present study demonstrates that the gene Arg-Ⅱ might participate in the immune response of Japanese flounder to E. tarda infection, thus indicating that the gene Arg-Ⅱ might play an important role in the antibacterial immunity of Japanese flounder.
