Characteristics of the interferon regulatory factor 5 (IRF5) and its expression in response to LCDV and poly I:C challenges in Japanese flounder, Paralichthys olivaceus.

Interferon regulatory factor 5 (IRF5) has been identified as a key transcriptional mediator regulating expression of both type I interferons (IFNs) and proinflammatory cytokines. In this study, the cDNA and genomic sequences of IRF5 were isolated from Japanese flounder, Paralichthys olivaceus. The gene of Japanese flounder (Jf)IRF5 is 7326 bp long, contains 9 exons and 8 introns and encodes a putative protein of 472 amino acids. The predicted protein sequence shares 61.1-81.9% identity to fish IRF5 and possesses a DNA-binding domain (DBD), a middle region (MR), an IRF association domain (IAD), a virus activated domain (VAD) and two nuclear localization signals (NLSs) conserved in all known IRF5s. Phylogenetic analysis clustered it into the teleost IRF5 subgroup within vertebrate IRF5 group. JfIRF5 mRNA was constitutively expressed in all tissues examined, with higher levels observed in the gills and head kidney. Gene expression of JfIRF5 was analyzed over a 7-day time course in the gills, head kidney, spleen and muscle of Japanese flounders challenged with lymphocystis disease virus (LCDV) and polyinosinic:polycytidylic acid (poly I:C). The data showed that JfIRF5 expression was slightly up-regulated by LCDV, but its induction time was clearly moved up; in contrast, the induction upon poly I:C challenge started not earlier than day 2 post-injection and was stronger and more persistent with a later peak time in all four organs. The late and long-lasting inductive expression of JfIRF5 following poly I:C challenge suggests that it might be an interferon stimulated gene (ISG), the induction of which is driven by poly I:C-induced type I IFNs.

An IRF-3 homolog that is up-regulated by DNA virus and poly I:C in turbot, Scophthalmus maximus.

In this study, we described the structure, mRNA tissue distribution and regulation of an IRF-3 gene from turbot, Scophthalmus maximus (SmIRF-3). The gene sequence of SmIRF-3 is 6077 bp long, composed of 11 exons and 10 introns similar to known IRF-3 genes of fish, and encodes a peptide of 466 amino acids. The deduced protein sequence shares the highest identity of 56.0-81.2% with fish IRF-3 and possesses a DNA-binding domain (DBD), an IRF association domain (IAD) and a serine-rich domain (SRD) known to be important for the functions of IRF-3 in vertebrates. Phylogenetic analysis grouped SmIRF-3 with other IRF3s of vertebrates. SmIRF-3 transcripts were detectable in limited tissue types of healthy fish, with higher expression observed in head, kidney, spleen and kidney,. The SmIRF-3 was transcriptionally up-regulated by turbot reddish body iridovirus (TRBIV) and polyinosinic:polycytidylic acid (poly I:C) in the head kidney, spleen and gills, with showing a two wave induced expression during a 7-day time course in all cases. The highest inducibility and the likely earliest increase of SmIRF-3 expression were observed in the spleen, and poly I:C was a stronger inducer. In addition, the maximal expression level of SmIRF-3 arose prior to that of the Mx in all the cases.