Hypermethylated genome of a fish vertebrate iridovirus ISKNV plays important roles in viral infection.

Iridoviruses are nucleocytoplasmic large dsDNA viruses that infect invertebrates and ectothermic vertebrates. The hypermethylated genome of vertebrate iridoviruses is unique among animal viruses. However, the map and function of iridovirus genomic methylation remain unknown. Herein, the methylated genome of Infectious spleen and kidney necrosis virus (ISKNV, a fish iridovirus), and its role in viral infection, are investigated. The methylation level of ISKNV is 23.44%. The hypermethylated genome is essential for ISKNV amplification, but there is no correlation between hypermethylation and viral gene expression. The hypomethylated ISKNV (obtained via 5-Azacytidine) activates a strong immunoreaction in vitro and reduces its pathogenicity in vivo. The unmethylated viral DNA can induce a stronger immunoreaction in vitro, whereas inactivated hypomethylated ISKNV can induce a stronger immunoreaction in vivo, suggesting ISKNV may evade from immune system by increasing its genome methylation level. Our work provides new insights into the role of genome methylation in viral infection.

Proteomic analysis of the Decapod iridescent virus 1.

Decapod iridescent virus 1 (DIV1) is one of the major pathogens of farmed shrimp. In this study, the structural proteins of DIV1 were analyzed by mass spectrometry. DIV1 virions were purified from the hemolymph of artificially infected Cherax quadricarinatus. The viral proteins were separated by sodium dodecyl sulfate-polyacrylamide gel electrophoresis, and a total of 28 protein bands were obtained. These protein bands were in-gel digested with trypsin and the resulting tryptic peptide mixtures were subjected to liquid chromatography with tandem mass spectrometry analysis. Thirty virus-encoded proteins were identified. Among them, 6 proteins were predicted to contain transmembrane domains, 3 proteins were predicted to contain an Arg-Gly-Asp motif. Nine proteins showed significant homology with functionally characterized proteins. Antibodies were produced for these candidate proteins and 23 of them were confirmed to be the components of DIV1 virions by Western blotting. This study provides the first proteomic analysis of DIV1, which establishes a foundation for further investigation of viral infection and replication.

Interaction between 038R and 125R of Cherax quadricarinatus iridovirus (CQIV) and their effects on virus replication.

Iridovirids are a group icosahedral viruses containing linear double-stranded DNA, and mainly infect invertebrates and poikilothermic vertebrates. Cherax quadricarinatus iridovirus (CQIV) is a new species of the family Iridoviridae and can cause high mortality in shrimps. In CQIV genome, there are 25 conserved genes and the putative products are involved in several viral processes. In this study, three core protein including CQIV-032R, CQIV-125R and CQIV-160L were identified to interact with CQIV-038R by yeast two-hybrid (Y2H), and the interaction between CQIV-038R and CQIV-125R was further confirmed by co-immunoprecipitation (Co-IP) assays. In the expression system, EGFP-038R and mCherry-125R were colocalized in the cytoplasm when co-expressed in Sf9 cells. Moreover, silencing the expression of 038R, 125R or both of these two proteins respectively in C. quadricarinatus cells by small interfering RNAs showed significantly inhibit CQIV replication. Collectively, we identified the interaction between 038R and 125R, and demonstrated they are essential for CQIV replication.

Interferon functional analog activates antiviral Jak/Stat signaling through integrin in an arthropod.

Drosophila Vago is a small antiviral peptide. Its ortholog in Culex mosquito was found to be an interferon-like cytokine that limits virus replication through activating Jak/Stat signaling. However, this activation is independent of Domeless, the sole homolog of vertebrate type I cytokine receptor. How Vago activates the Jak/Stat pathway remains unknown. Herein, we report this process is dependent on integrin in kuruma shrimp (Marsupenaeus japonicus). Shrimp Vago-like (MjVago-L) plays an antiviral role by activating the Jak/Stat pathway and inducing Stat-regulated Ficolin. Blocking integrin abrogates the role of MjVago-L. The interaction between MjVago-L and integrin ß3 is confirmed. An Asp residue in MjVago-L is found critical for the interaction and MjVago-L's antiviral role. Moreover, Fak, a key adaptor of integrin signaling, mediates MjVago-L-induced Jak/Stat activation. Therefore, this study reveals that integrin, as the receptor of MjVago-L, mediates Jak/Stat activation. The establishment of the MjVago-L/integrin/Fak/Jak/Stat/Ficolin axis provides insights into antiviral cytokine signaling in invertebrates.