Temperature-regulated typeⅡgrass carp reovirus establishes latent infection in Ctenopharyngodon idella brain

Grass carp reovirus(GCRV)causes extensive infection and death in grass carp and black carp fingerlings,with a highly seasonal prevalence.Previous studies suggested that GCRV can become latent after primary infection.In this study,we investigated type II GCRV(GCRV-II)latency in asymptomatic grass carp with GCRV infection or exposure history.We found that during latent infection,GCRV-II was detectable only in the brain of grass carp,unlike the multi-tissue distribution observed in natural infection.GCRV-II only caused damage to the brain during latent infection,while in natural infection,brain,heart,and eye tissues had relatively higher viral loads.We also discovered viral inclusion bodies in infected fish brains.Additionally,GCRV-II distribution in grass carp was notably affected by ambient temperature,with the virus targeting the brain only during low temperatures and multi-tissue distribution during high temperatures.This study provides insights into the mechanisms of GCRV-II latent infection and reactivation and contributes to the prevention and control of GCRV pandemics.

Characterization of viral entry and infection of quantum dot-labeled grass carp reovirus

Dear Editor,Reoviruses are non-enveloped icosahedral virions with an outer capsid surrounding their cores,which harbor the10–12 segmented double-stranded RNA(ds RNA)genome.To date,there are 15 proposed genera in the family Reoviridae(King et al.,2012),including Aquareovirus.Generally,aquareoviruses are of low pathogenicity in aquaculture.However,grass carp reovirus(GCRV)is

Oral PLGA-based DNA vaccines using interferons as adjuvants remarkably promote the immune protection of grass carp(Ctenopharyngodon idella)against GCRV infection

Grass carp hemorrhagic disease caused by grass carp reovirus(GCRV)results in significant economic losses to the global grass carp aquaculture industry.Oral vaccination is an ideal choice for disease precaution in aquaculture.However,oral vaccine can be degraded in the gut.Therefore,the selection of loading materials is essential.In this study,the S6 and S7 fragments(encoding the outer capsid protein VP4 and fibronectin VP56 of GCRV)and grass carp interferons(IFNs),including IFN1,IFN3,and IFNγ2 were used to create DNA vaccines and adjuvants based on pcDNA3.1,respectively.The oral DNA vaccine was encapsulated in poly(lactic-co-glycolic acid)(PLGA)and polyvinyl alcohol(PVA)with IFNs.The PLGA-PVA(PP)nano-microspheres were prepared by double emulsionsolvent evaporation technique.Using transmission electron microscopy and dynamic light scattering assays,it was determined the vaccines had a spherical structure with uniform particle size(643.5±35.3 nm).The nanomicrospheres possessed excellent encapsulation efficiency(81.6±2.6%)and loading rate(0.54±0.02%),and simultaneously exhibited negligible hemolytic activity and cell toxicity.The protection rate and tissue viral loads post-GCRV challenge in grass carp were assessed.The oral PP nano-microsphere with pVP4 t pIFN1(PP41)vaccine increased protection rate by 44%compared with the control group and was correlated with relatively low viral loads in the spleen,head kidney,and hindgut.Further,three crucial serum biochemical indexes,total superoxide dismutase(TSOD),complement C3(C3),and lysozyme(LZM),were also dramatically increased.Furthermore,mRNA expressions of representative immune-related genes(IgM,IFN1,IFNγ2,MHC-I,and CD8α)in the head kidney and spleen were significantly enhanced.In addition,mRNA expression of IgT was significantly boosted in the hindgut.The results indicate that DNA vaccine capsulated with PP is effective against GCRV infection.The present study provides insights into a prospective strategy for oral vaccine development in aquaculture.

Characterization of grass carp FosB, Fosl2, JunD transcription factors in response to GCRV infection

Activating protein-1(AP-1)composed of Jun and Fos family proteins,which are frequently activated by pathogens to induce cellular inflammation and immune responses.In this study,by using RNA sequencing(RNA-seq)technology,we found that FosB,Fosl2,and JunD expression was co-induced 12 and 20 h in grass carp(Ctenopharyngodon idella)kidney cell line(CIK cells)after grass carp reovirus(GCRV)infection.Full-length cDNA of the three genes were cloned and phylogenetic analysis indicated that the corresponding proteins shared high homology with those in higher vertebrates.The tissue distribution analysis of the three genes showed they were ubiquitously expressed in various tissues of healthy grass carp.In infection assay,FosB,Fosl2,and JunD were up-regulated and co-expressed 8 h after GCRV infection in CIK cells.Protein interaction and co-expression network analysis revealed that FosB,Fosl2,and JunD showed similar functions and were co-expressed in mammals and fish.Taken together,these results indicated that the co-expression of the AP-1 family proteins in grass carp uniformly responds to GCRV infection.These findings provided insights into the further study of AP-1 transcription factors function during grass carp reovirus infection.

GCRV NS38 counteracts SVCV proliferation by intracellular antagonization during co-infection

Viral co-infection has been found in animals;however,the mechanisms of co-infection are unclear.The abundance and diversity of viruses in water make fish highly susceptible to co-infection.Here,we reported a coinfection in fish,which resulted in reduced host lethality and illustrated the intracellular molecular mechanism of viral co-infection.The spring viremia of carp virus(SVCV)is a highly lethal virus that infects Cyprinidae,such as zebrafish.The mortality of SVCV infection was significantly reduced when co-infected with the grass carp reovirus(GCRV).The severity of tissue damage and viral proliferation of SVCV was also reduced in co-infection with GCRV.The transcriptome bioinformatics analysis demonstrated that the effect on the host transcripts in response to SVCV infection was significantly reduced in co-infection.After excluding the extracellular interactions of these two viruses,the intracellular mechanisms were studied.We found that the GCRV NS38 remarkably decreased SVCV infection and viral proliferation.The interaction between GCRV NS38 and SVCV nucleoprotein(N)and phosphoprotein(P)proteins was identified,and NS38 downregulated both N and P proteins.Further analysis demonstrated that the N protein was degraded by NS38 indispensable of the autophagy receptor,sequestosome 1(p62).Meanwhile,K63-linked ubiquitination of the P protein was reduced by NS38,leading to ubiquitinated degradation of the P protein.These results reveal that the intracellular viral protein interactions are a crucial mechanism of co-infection and influence the host pathology and expand our understanding in intracellular viral interactions co-infection.

Dynamic localization and the associated translocation mechanism of HMGBs in response to GCRV challenge in CIK cells

High-mobility group box （HMGB） proteins, a family of chromatin-associated nuclear proteins, play amazingly multifaceted roles in the immune system of mammals. Thus far, little is known about the nucleocytoplasmic distribution of HMGBs in teleosts. The present study systematically investigated the dynamic localization of all six HMGB proteins in Ctenopharyngodon idella kidney （CIK） cells. Under basal conditions, all HMGBs exclusively localized to the nucleus. Grass carp reovirus （GCRV）, polyinosinic-polycytidylic （poly（I ： C）） potassium salt and lipopolysaccharide （LPS） challenge evoked the nuclear export of HMGBs to various degrees： GCRV challenge induced the highest nuclear export of CiHMGB2b, and poly（I ~ C） and LPS evoked the highest nucleocytoplasmic shuttling of CiHMGBlb. Overall, the nucleocytoplasmic shuttling of CiHMGB2a and CiHMGB3b was rarely induced by these challenges. Dynamic imaging uncovered that the nucleocytoplasmic GCRV-induced relocation of CiHMGB2b occurred in cells undergoing karyotheca rupture, apoptosis or proliferation. Western blot analyses were used to examine HMGB-EGFP fusion proteins in whole cell lysates, cytosol, nuclear fractions and culture medium. Further investigation demonstrated the nuclear retention of N-terminal HMG-boxes and the nucleocytoplasmic distribution of the C-terminal acidic tails. Comparative analyses of the dynamic relocation of full-length, truncated or chimeric HMGBs confirmed that the intramolecular interaction between HMG-boxes and C-tail domains mediated the nucleocytoplasmic translocation of HMGBs. These results not only provide an overall understanding of the subcellular localization of HMGBs, but also reveal the induction mechanism of the nucleocytoplasmic translocation of HMGBs by GCRV challenge, which lays a foundation for further studies on the interactions among pathogens, HMGBs and pattern recognition receptors in the innate immunity of teleosts.

GCRV 096 VP6 protein and its impacts on GCRV replication with different genotypes in CIK cells

Grass carp reovirus(GCRV)is the causative agent of grass carp hemorrhagic disease,which has detrimental effects on the grass carp aquaculture industry.There are four known genotypes of GCRV and strains of different GCRV genotypes differ greatly.In this study,the diversity of the protein VP6 from different GCRV stains and the effect of genotype GCRV 096 on replication was investigated in CIK cells.Our results showed that the VP6 protein of GCRV 096(genotypeІ)exhibited limited homology to that of GCRV GD108(genotypeШ),with few residues conserved in predicted protein-protein interaction domains.GCRV 096 VP6 protein was expressed and purified and an antiserum against it was characterized.Addition of purified VP6 protein or antiserum to culture media of CIK cells inhibited the replication of GCRV 096 in these cells.In contrast,replication of GCRV GD108(genotypeШ)was not affected in CIK cells under the same condition.Overall,our results indicated that the protein VP6 and VP6 antiserum did not provide cross-protection against GCRV strains and this can be attributed to differences among GCRV genotypes.It will be important to consider multiple GCRV genotypes in the development of effective GCRV vaccines and other therapies against grass carp hemorrhagic disease.In addition,bioinformatics analysis also suggested that the protein VP6 may have a role in the process of GCRV infection.This study lays the foundation for the prevention of grass carp hemorrhagic disease and further detailed studies on the pathogenesis of GCRV.