Suppression of RNA interference pathway in vitro by Grass carp reovirus

The destiny of the resistance/susceptibility against GCRV is controlled by epigenetic mechanisms in CIK cells

Hemorrhagic disease caused by grass carp reovirus (GCRV) has severely threatened the grass carp (Ctenopharyngodon idella) cultivation industry. It is noteworthy that the resistance against GCRV infection was reported to be inheritable, and identified at both individual and cellular levels. Therefore, this work was inspired and dedicated to unravel the molecular mechanisms of fate decision post GCRV infection in related immune cells. Foremost, the resistant and susceptible CIK (C. idella kidney) monoclonal cells were established by single cell sorting, subculturing and infection screening successively. RNA-Seq, MeDIP-Seq and small RNA-Seq were carried out with C1 (CIK cells), R2 (resistant cells) and S3 (susceptible cells) groups. It was demonstrated that genome-wide DNA methylation, mRNA and microRNA expression levels in S3 were the highest among three groups. Transcriptome analysis elucidated that pathways associated with antioxidant activity, cell proliferation regulation, apoptosis activity and energy consuming might contribute to the decision of cell fates post infection. And a series of immune-related genes were identified differentially expressed across resistant and susceptible groups, which were negatively modulated by DNA methylation or microRNAs. To conclude, this study systematically uncovered the regulatory mechanism on the resistance from epigenetic perspective and provided potential biomarkers for future studies on resistance breeding.

Sequestration of RNA by grass carp Ctenopharyngodon idella TIA1 is associated with its positive role in facilitating grass carp reovirus infection

Previous report demonstrated that grass carp reovirus (GCRV) infection resulted in unlinking cellular stress granule formation from aggregation of grass carp Ctenopharyngodon idella TIA1 (CiTIA1). Here, we provided evidence to show that CiTIA1 bound to synthesized ssRNA and dsRNA in vitro. Both GST-pull down assay and RNA immunoprecipitation analysis confirmed the association between GCRV-specific RNA and GST-tagged CiTIA1 in C. idella kidney (CIK) cells. Furthermore, CiTIA1 was shown to protect dsRNA of virus-origin from degradation in CIK cells through Northern blot analysis. Finally, transient overexpression of CiTIA1 enhanced the replication efficiency of GCRV in CIK cells. Taken together, our results suggested that cellular CiTIA1 might facilitate GCRV replication through sequestrating and protecting viral RNA from degradation.

Insights into the antiviral immunity against grass carp (Ctenopharyngodon idella) reovirus (GCRV) in grass carp

Global fish production from aquaculture has rapidly grown over the past decades, and grass carp shares the largest portion. However, hemorrhagic disease caused by grass carp reovirus (GCRV) results in tremendous loss of grass carp (Ctenopharyngodon idella) industry. During the past years, development of molecular biology and cellular biology technologies has promoted significant advances in the understanding of the pathogen and the immune system. Immunoprophylaxis based on stimulation of the immune system of fish has also got some achievements. In this review, authors summarize the recent progresses in basic researches on GCRV; viral nucleic acid sensors, high-mobility group box proteins (HMGBs); pattern recognition receptors (PRRs), Toll-like receptors (TLRs) and retinoic acid inducible gene I- (RIG-I-) like receptors (RLRs); antiviral immune responses induced by PRRs-mediated signaling cascades of type I interferon (IFN-I) and IFN-stimulated genes (ISGs) activation. The present review also notices the potential applications of molecule genetic markers. Additionally, authors discuss the current preventive and therapeutic strategies (vaccines, RNAi, and prevention medicine) and highlight the importance of innate immunity in long term control for grass carp hemorrhagic disease.

Quantitative in vivo and in vitro characterization of co-infection by two genetically distant grass carp reoviruses

Grass carp reovirus (GCRV) is one of the most serious pathogens threatening grass carp (Ctenopharyngodon idella) production in China. Through sequence analysis, the co-existence of two genetically distant grass carp reoviruses, named GCRV-JX01 and GCRV-JX02, was revealed in the same diseased grass carp sample collected in 2011. GCRV-JX01 and GCRV-JX02 shared high levels of homology with GCRV-873 and GCRV-GD108, respectively. In contrast to GCRV-JX01, GCRV-JX02 induced no cytopathic effect in infected cells. A quantitative real-time PCR assay was employed to monitor the replication efficiency of both virus strains in either Ctenopharyngodon idella kidney (CIK) cells or infected cell supernatant. The results demonstrated that, although GCRV-JX02 did reduce the cellular replication level of GCRV-JX01 up to 10-fold during co-infection, there was no significant impact on the productive virus progeny level in supernatant compared to that of cells infected by GCRV-JX01 alone. To validate the hypothesis that both viruses might co-infect grass carp without significant interference in the field, we collected clinical samples from two different fish farms in 2012 and monitored virus loads for each fish. The data showed that 55 % of the collected fish samples were co-infected by GCRV-JX01 and GCRV-JX02, and the single virus infection rate was 10 % for GCRV-JX01 and 20 % for GCRV-JX02. For both viruses, the in vivo viral loads under co-infection and single viral infection were similar. No serological cross-reaction or cross-protection occurred between GCRV-JX01 and JX02 in our immunization and challenge tests. This new information on co-infection by two genetically distant virus strains should be helpful for designing vaccines targeting the causative agents of grass carp haemorrhagic disease.