Molecular Cloning And Expression Analysis Of IRF-5in Japanese Flounder, Paralichthys Olivaceus

Japanese flouder (Paralichthys olivaceus), one of the most importantmaricultured species in Northeast Asia, has been suffered from serious diseases,especially viral disease, in recent years with the development of the indoors breeding.The viral diseases has led to great economic loss in the flounder culture. IFN plays animportant role in antiviral immune. Consequently, the aim of this study is to enrich theknowledge about the IFN system of flounder which will be help to control viraldiseases of this commercially important species.Interferon regulatory factor5(IRF-5) has been identified as a key transcriptionalmediator regulating expression of both type Ⅰinterferons (IFNs) andproinflammatory cytokines. In this study, We used the homologous PCR and RapidAmplification of cDNA Ends（RACE）method to isolate the cDNA and genomicsequences of irf5from the spleen of Japanese flounder, Paralichthys olivaceus. TheJapanese flounder irf5cDNA consisted of1869nucleotides and encodes a putativeprotein of472amino acids. The gene of Japanese flounder irf5is3566bp long,containing9exons and8introns. The predicted protein sequence shares61.1-81.9%identity to fish IRF-5and possesses a DNA-binding domain (DBD), a middle region(MR), an IRF association domain (IAD), a virus activated domain (VAD) and twonuclear localization signals (NLSs) conserved in all known IRF-5s. Phylogeneticanalysis clustered it into the teleost IRF-5subgroup within vertebrate IRF5group.Japanese flounder irf5mRNA was detected to be constitutively expressed in all tissuesexamined, with higher levels observed in the gills and head kidney, lower levels in thebrain, liver and skin. Gene expression of Japanese flounder irf5was analyzed over a7-day time course in the gills, head kidney, spleen and muscle of Japanese flounderschallenged with lymphocystis disease virus (LCDV) and polyinosinic: polycytidylic acid (poly I:C). The data showed that the expression of Japanese flounder irf5genewas slightly up-regulated by LCDV, but its induction time was clearly moved up; incontrast, the induction upon poly I:C challenge started not earlier than day2post-injection and was stronger and more persistent with a later peak time in all fourorgans. The late and long-lasting inductive expression of irf5following poly I:Cchallenge suggests that it might be an interferon stimulated gene (ISG), the inductionof which is driven by poly I:C-induced type Ⅰ IFNs.Our findings contribute to an better understanding of the IFN system in Japaneseflouder and help to develop effective strateges for protection Japanese flouder fromviral diseases.