Reovirus infection induces transcriptome-wide unique A-to-I editing changes in the murine fibroblasts.

The conversion of Adenosine (A) to Inosine (I), by Adenosine Deaminases Acting on RNA or ADARs, is an essential post-transcriptional modification that contributes to proteome diversity and regulation in metazoans including humans. In addition to its transcriptome-regulating role, ADARs also play a major part in immune response to viral infection, where an interferon response activates interferon-stimulated genes, such as ADARp150, in turn dynamically regulating host-virus interactions. A previous report has shown that infection from reoviruses, despite strong activation of ADARp150, does not influence the editing of some of the major known editing targets, while likely editing others, suggesting a potentially nuanced editing pattern that may depend on different factors. However, the results were based on a handful of selected editing sites and did not cover the entire transcriptome. Thus, to determine whether and how reovirus infection specifically affects host ADAR editing patterns, we analyzed a publicly available deep-sequenced RNA-seq dataset, from murine fibroblasts infected with wild-type and mutant reovirus strains that allowed us to examine changes in editing patterns on a transcriptome-wide scale. To the best of our knowledge, this is the first transcriptome-wide report on host editing changes after reovirus infection. Our results demonstrate that reovirus infection induces unique nuanced editing changes in the host, including introducing sites uniquely edited in infected samples. Genes with edited sites are overrepresented in pathways related to immune regulation, cellular signaling, metabolism, and growth. Moreover, a shift in editing targets has also been observed, where the same genes are edited in infection and control conditions but at different sites, or where the editing rate is increased for some and decreased for other differential targets, supporting the hypothesis of dynamic and condition-specific editing by ADARs.

Effect of Heat Shock Treatment on the Virulence of Grass Carp Reovirus in Rare Minnow Gobiocypris rarus.

The mode and outcome of fish-virus interactions are influenced by many abiotic factors, among which water temperature is especially important in poikilothermic fish. Rare minnow Gobiocypris rarus is a eurythermal small cyprinid fish that is sensitive to infection with genotype II grass carp reovirus (GCRV). HSP70, a conservative and key player in heat shock response, is previously identified as an induced pro-viral factor during GCRV infection in vitro. Here, rare minnow was subjected to heat shock treatment (HST), 1 h treatment at 32 °C followed by reverting to a normal temperature of 24 °C, and subsequently challenged with GCRV-II at a dosage of 1 × LD50. The effect of HST on GCRV virulence in vivo was evaluated by calculating virus-associated mortality and viral load in both dead and survival fish. The results revealed that HST enhanced the mortality of rare minnow infected with GCRV; the fact that viral loads in the tissue samples of HST-treated fish were significantly higher than those in samples of the control group at 6, 8 d p.i. reflected a faster infection process due to HST. Quantitative gene expression analysis was further employed to show that the expression levels of Hsp70 in intestine and liver tissues from the HST group declined faster than muscle tissue after HST. HST W/O GCRV challenge upregulated proinflammatory cytokines such as MyD88 and Nf-κB, which was in consistence with the inflammation observed in histopathological analysis. This study shed light on the complexity of the interaction between fish abiotic and biotic stress response, which suggested that HST, an abiotic stress, could enhance the virulence of GCRV in Gobiocypris rarus that involved modulating the gene expression of host heat shock, as well as a pro-inflammatory response.

Comparative Analysis of mRNA, microRNA of Transcriptome, and Proteomics on CIK Cells Responses to GCRV and Aeromonas hydrophila.

Grass Carp Reovirus (GCRV) and Aeromonas hydrophila (Ah) are the causative agents of haemorrhagic disease in grass carp. This study aimed to investigate the molecular mechanisms and immune responses at the miRNA, mRNA, and protein levels in grass carp kidney cells (CIK) infected by Grass Carp Reovirus (GCRV, NV) and Aeromonas hydrophilus (Bacteria, NB) to gain insight into their pathogenesis. Within 48 h of infection with Grass Carp Reovirus (GCRV), 99 differentially expressed microRNA (DEMs), 2132 differentially expressed genes (DEGs), and 627 differentially expressed proteins (DEPs) were identified by sequencing; a total of 92 DEMs, 3162 DEGs, and 712 DEPs were identified within 48 h of infection with Aeromonas hydrophila. It is worth noting that most of the DEGs in the NV group were primarily involved in cellular processes, while most of the DEGs in the NB group were associated with metabolic pathways based on KEGG enrichment analysis. This study revealed that the mechanism of a grass carp haemorrhage caused by GCRV infection differs from that caused by the Aeromonas hydrophila infection. An important miRNA-mRNA-protein regulatory network was established based on comprehensive transcriptome and proteome analysis. Furthermore, 14 DEGs and 6 DEMs were randomly selected for the verification of RNA/small RNA-seq data by RT-qPCR. Our study not only contributes to the understanding of the pathogenesis of grass carp CIK cells infected with GCRV and Aeromonas hydrophila, but also serves as a significant reference value for other aquatic animal haemorrhagic diseases.

The dexd/H-box helicase DHX40 is a novel negative regulator during GCRV infection via targeting the host RLR helicases and viral nonstructural protein NS38.

RLR helicases RIG-I and MDA5, which are known as pattern recognition receptors to sense cytoplasmic viral RNAs and trigger antiviral immune responses, are DExD/H-box helicases. In teleost, whether and how non-RLR helicases regulate RLR helicases to affect viral infection remains unclear. Here, we report that the non-RLR helicase DHX40 from grass carp (namely gcDHX40) is a negative regulator of grass carp reovirus (GCRV) infection and RLR-mediated type I IFN production. GcDHX40 was a cytoplasmic protein. Ectopic expression of gcDHX40 facilitated GCRV replication and suppressed type I IFN production induced by GCRV infection and by those genes involved the RLR antiviral signaling pathway. Mechanistically, gcDHX40 promoted the generation of viral inclusion bodies (VIBs) by interacting with the NS38 protein of GCRV. Additionally, gcDHX40 interacted with RLR helicase, and impaired the formation of RLR-MAVS functional complexes. Taken together, our results indicate that gcDHX40 is a novel important proviral host factor involving in promoting the generation of GCRV VIBs and inhibiting the production of RLR-mediated type I IFNs.

Arboviruses antagonize insect Toll antiviral immune signaling to facilitate the coexistence of viruses with their vectors.

Many plant arboviruses are persistently transmitted by piercing-sucking insect vectors. However, it remains largely unknown how conserved insect Toll immune response exerts antiviral activity and how plant viruses antagonize it to facilitate persistent viral transmission. Here, we discover that southern rice black-streaked dwarf virus (SRBSDV), a devastating planthopper-transmitted rice reovirus, activates the upstream Toll receptors expression but suppresses the downstream MyD88-Dorsal-defensin cascade, resulting in the attenuation of insect Toll immune response. Toll pathway-induced the small antibacterial peptide defensin directly interacts with viral major outer capsid protein P10 and thus binds to viral particles, finally blocking effective viral infection in planthopper vector. Furthermore, viral tubular protein P7-1 directly interacts with and promotes RING E3 ubiquitin ligase-mediated ubiquitinated degradation of Toll pathway adaptor protein MyD88 through the 26 proteasome pathway, finally suppressing antiviral defensin production. This virus-mediated attenuation of Toll antiviral immune response to express antiviral defensin ensures persistent virus infection without causing evident fitness costs for the insects. E3 ubiquitin ligase also is directly involved in the assembly of virus-induced tubules constructed by P7-1 to facilitate viral spread in planthopper vector, thereby acting as a pro-viral factor. Together, we uncover a previously unknown mechanism used by plant arboviruses to suppress Toll immune response through the ubiquitinated degradation of the conserved adaptor protein MyD88, thereby facilitating the coexistence of arboviruses with their vectors in nature.

Neuropilin invites reoviruses into neurons.

In this issue of Cell Host & Microbe, Shang et al. identify murine neuropilin 1 as a host factor that binds reovirus particles, directing cell entry and contributing to viral dissemination and neurovirulence. This study highlights the reovirus model system to investigate host receptors and their significance in viral pathogenesis.

The role of MASP1 in the complement system and expression characteristics in response to GCRV infection in grass carp.

The grass carp (Ctenopharyngodon idella) constitutes a significant economic resource within the aquaculture sector of our nation, yet it has been chronically afflicted by the Grass Carp Reovirus (GCRV) disease. The complement system, a vital component of fish's innate immunity, plays a crucial role in combating viral infections. This research investigates the potential role of MASP1, a key molecule in the lectin pathway of the complement system, in the GCRV infection in grass carp. An analysis of the molecular characteristics of MASP1 in grass carp revealed that its identity and similarity percentages range from 35.10 to 91.00 % and 35.30-91.00 %, respectively, in comparison to other species. Phylogenetically, MASP1 in C. idella aligns closely with species such as Danio rerio, Cyprinus carpio, and Carassius carassius, exhibiting chromosomal collinearity with the zebrafish. Subsequent tissue analysis in both healthy and GCRV-infected grass carp indicated that MASP1's basal expression was predominantly in the liver. Post-GCRV infection, MASP1 expression in various tissues exhibited temporal variations: peaking in the liver on day 5, spleen on day 7, and kidney on day 14. Furthermore, employing Complement Component 3 (C3) as a benchmark for complement system activation, it was observed that MASP1 could activate and cleave C3 to C3b. MASP1 also demonstrated an inhibitory effect on GCRV replication (compared with the control group, VP2 and VP7 decreased by 6.82-fold and 4.37-fold) and enhanced the expression of antiviral genes, namely IRF3, IRF7 and IFN1 (compared with the control group, increased 2.25-fold, 45.38-fold and 22.37-fold, respectively). In vivo protein injection experiments substantiated MASP1's influence on the relative mRNA expression levels of C3 in various tissues and its protein expression in serum. This study also verified that C3 could modulate the expression of antiviral genes such as IFN1 and IRF3.

Analysis of tissue tropism of GCRV-II infection in grass carp using a VP35 monoclonal antibody.

Grass carp, one of the major freshwater aquaculture species in China, is susceptible to grass carp reovirus (GCRV). GCRV is a non-enveloped RNA virus and has a double-layered capsid, causing hemorrhagic disease and high mortalities in infected fish. However, the tropism of GCRV infection has not been investigated. In this study, monoclonal antibodies against recombinant VP35 protein were generated in mice and characterized. The antibodies exhibited specific binding to the N terminal region (1-155 aa) of the recombinant VP35 protein expressed in the HEK293 cells, and native VP35 protein in the GCRV-II infected CIK cells. Immunofluorescent staining revealed that viruses aggregated in the cytoplasm of infected cells. In vivo challenge experiments showed that high levels of GCRV-II viruses were present in the gills, intestine, spleen and liver, indicating that they are the major sites for virus infection. Our study showed that the VP35 antibodies generated in this study exhibited high specificity, and are valuable for the development of diagnostic tools for GCRV-II infection.

Fluorescent protein tags affect the condensation properties of a phase-separating viral protein.

Fluorescent protein (FP) tags are extensively used to visualize and characterize the properties of biomolecular condensates despite a lack of investigation into the effects of these tags on phase separation. Here, we characterized the dynamic properties of µNS, a viral protein hypothesized to undergo phase separation and the main component of mammalian orthoreovirus viral factories. Our interest in the sequence determinants and nucleation process of µNS phase separation led us to compare the size and density of condensates formed by FP::µNS to the untagged protein. We found an FP-dependent increase in droplet size and density, which suggests that FP tags can promote µNS condensation. To further assess the effect of FP tags on µNS droplet formation, we fused FP tags to µNS mutants to show that the tags could variably induce phase separation of otherwise noncondensing proteins. By comparing fluorescent constructs with untagged µNS, we identified mNeonGreen as the least artifactual FP tag that minimally perturbed µNS condensation. These results show that FP tags can promote phase separation and that some tags are more suitable for visualizing and characterizing biomolecular condensates with minimal experimental artifacts.

Grass carp (Ctenopharyngodon idella) NIK up-regulates the expression of IL-8 by activating the NF-κB canonical pathway.

NIK (NF-κB inducing kinase) belongs to the mitogen-activated protein kinase family, which activates NF-κB and plays a vital role in immunology, inflammation, apoptosis, and a series of pathological responses. In NF-κB noncanonical pathway, NIK and IKKα have been often studied in mammals and zebrafish. However, few have explored the relationship between NIK and other subunits of the IKK complex. As a classic kinase in the NF-κB canonical pathway, IKKß has never been researched with NIK in fish. In this paper, the full-length cDNA sequence of grass carp (Ctenopharyngodon idella) NIK (CiNIK) was first cloned and identified. The expression level of CiNIK in grass carp cells was increased under GCRV stimuli. Under the stimulation of GCRV, poly (I:C), and LPS, the expression of NIK in various tissues of grass carp was also increased. This suggests that CiNIK responds to viral stimuli. To study the relationship between CiNIK and CiIKKß, we co-transfected CiNIK-FLAG and CiIKKB-GFP into grass carp cells in coimmunoprecipitation and immunofluorescence experiments. The results revealed that CiNIK interacts with CiIKKß. Besides, the degree of autophosphorylation of CiNIK was enhanced under poly (I:C) stimulation. CiIKKß was phosphorylated by CiNIK and then activated the activity of p65. The activity change of p65 indicates that NF-κB downstream inflammatory genes will be functioning. CiNIK or CiIKKß up-regulated the expression of IL-8. It got higher when CiNIK and CiIKKß coexisted. This paper revealed that NF-κB canonical pathway and noncanonical pathway are not completely separated in generating benefits.

IL-6/STAT3 axis is hijacked by GCRV to facilitate viral replication via suppressing type â IFN signaling.

Grass carp reovirus (GCRV) infections and hemorrhagic disease (GCHD) outbreaks are typically seasonally periodic and temperature-dependent, yet the molecular mechanism remains unclear. Herein, we depicted that temperature-dependent IL-6/STAT3 axis was exploited by GCRV to facilitate viral replication via suppressing type Ⅰ IFN signaling. Combined multi-omics analysis and qPCR identified IL-6, STAT3, and IRF3 as potential effector molecules mediating GCRV infection. Deploying GCRV challenge at 18 °C and 28 °C as models of resistant and permissive infections and switched to the corresponding temperatures as temperature stress models, we illustrated that IL-6 and STAT3 expression, genome level of GCRV, and phosphorylation of STAT3 were temperature dependent and regulated by temperature stress. Further research revealed that activating IL-6/STAT3 axis enhanced GCRV replication and suppressed the expression of IFNs, whereas blocking the axis impaired viral replication. Mechanistically, grass carp STAT3 inhibited IRF3 nuclear translocation via interacting with it, thus down-regulating IFNs expression, restraining transcriptional activation of the IFN promoter, and facilitating GCRV replication. Overall, our work sheds light on an immune evasion mechanism whereby GCRV facilitates viral replication by hijacking IL-6/STAT3 axis to down-regulate IFNs expression, thus providing a valuable reference for targeted prevention and therapy of GCRV.

Deep sequencing identified miR-193b-3p as a positive regulator of autophagy targeting Akt3 in Ctenopharyngodon idella CIK cells during GCRV infection.

Recent research has highlighted complex and close interaction between miRNAs, autophagy, and viral infection. In this study, we observed the autophagy status in CIK cells infected with GCRV at various time points. We found that GCRV consistently induced cellar autophagy from 0 h to 12 h post infection. Subsequently, we performed deep sequencing on CIK cells infected with GCRV at 0 h and 12 h respectively, identifying 38 DEMs and predicting 9581 target genes. With the functional enrichment analyses of GO and KEGG, we identified 35 autophagy-related target genes of these DEMs, among which akt3 was pinpointed as the most central hub gene using module assay of the PPI network. Then employing the miRanda and Targetscan programs for prediction, and verification through a double fluorescent enzyme system and qPCR method, we confirmed that miR-193 b-3p could target the 3'-UTR of grass carp akt3, reducing its gene expression. Ultimately, we illustrated that grass carp miR-193 b-3p could promote autophagy in CIK cells. Above results collectively indicated that miRNAs might play a critical role in autophagy of grass carp during GCRV infection and contributed significantly to antiviral immunity by targeting autophagy-related genes. This study may provide new insights into the intricate mechanisms involved in virus, autophagy, and miRNAs.

Virus discovery in cultured portunid crabs: Genomic, phylogenetic, histopathological and microscopic characterization of a reovirus and a new bunyavirus.

Portunid crabs are distributed worldwide and highly valued in aquaculture. Viral infections are the main limiting factor for the survival of these animals and, consequently, for the success of commercial-scale cultivation. However, there is still a lack of knowledge about the viruses that infect cultured portunid crabs worldwide. Herein, the genome sequence and phylogeny of Callinectes sapidus reovirus 2 (CsRV2) are described, and the discovery of a new bunyavirus in Callinectes danae cultured in southern Brazil is reported. The CsRV2 genome sequence consists of 12 dsRNA segments (20,909 nt) encode 13 proteins. The predicted RNA-dependent RNA polymerase (RdRp) shows a high level of similarity with that of Eriocheir sinensis reovirus 905, suggesting that CsRV2 belongs to the genus Cardoreovirus. The CsRV2 particles are icosahedral, measuring approximately 65 nm in diameter, and exhibit typical non-turreted reovirus morphology. High throughput sequencing data revealed the presence of an additional putative virus genome similar to bunyavirus, called Callinectes danae Portunibunyavirus 1 (CdPBV1). The CdPBV1 genome is tripartite, consisting of 6,654 nt, 3,120 nt and 1,656 nt single-stranded RNA segments that each encode a single protein. Each segment has a high identity with European shore crab virus 1, suggesting that CdPBV1 is a new representative of the family Cruliviridae. The putative spherical particles of CdPBV1 measure ∼120 nm in diameter and present a typical bunyavirus morphology. The results of the histopathological analysis suggest that these new viruses can affect the health and, consequently, the survival of C. danae in captivity. Therefore, the findings reported here should be used to improve prophylactic and pathogen control practices and contribute to the development and optimization of the production of soft-shell crabs on a commercial scale in Brazil.

Rice varietal resistance to the vector Sogatella furcifera hinders transmission of Southern rice black-streaked dwarf virus.

BACKGROUND: The Southern rice black-streaked dwarf virus (SRBSDV) transmitted by Sogatella furcifera constitutes a threat to sustainable rice production. However, most rice varieties are highly vulnerable to SRBSDV, whereas the occurrence of the viral disease varies significantly under field conditions. This study aimed to evaluate the potential of rice varietal resistance to S. furcifera in reducing SRBSDV transmission. RESULTS: Among the five rice varieties, Zhongzheyou8 and Deyou108 exhibited high resistance to S. furcifera, Baixiangnuo33 was susceptible, and TN1 and Diantun502 were highly susceptible. The S. furcifera generally showed non-preference for and low feeding on the Zhongzheyou8 and Deyou108 plants, which may explain the resistance of these varieties to S. furcifera. Transmission of SRBSDV by S. furcifera was significantly impaired on the resistant varieties, both inoculation and acquisition rates were much lower on Zhongzheyou8 than on TN1. The short durations of S. furcifera salivation and phloem-related activities and the low S. furcifera feeding amount may explain the reduced SRBSDV inoculation and acquisition rates associated with Zhongzheyou8. Spearman's rank correlation revealed a significant negative correlation between S. furcifera resistance and SRBSDV transmission among the tested varieties. CONCLUSION: The results indicate that rice varietal resistance to the vector S. furcifera hinders SRBSDV transmission, which is largely associated with the host plant selection and feeding behaviors of the vector. The current findings shed light on the management of the SRBSDV viral disease through incorporation of S. furcifera resistant rice varieties in the management protocol. © 2024 Society of Chemical Industry.

Evaluating a combination treatment of NK cells and reovirus against bladder cancer cells using an in vitro assay to simulate intravesical therapy.

Intravesical treatment using either reovirus or natural killer (NK) cells serves as an efficient strategy for the treatment of bladder cancer cells (BCCs); however, corresponding monotherapies have often shown modest cytotoxicity. The potential of a locoregional combination using high-dose reovirus and NK cell therapy in an intravesical approach has not yet been studied. In this study, we evaluated the effectiveness of reoviruses and expanded NK cells (eNK) as potential strategies for the treatment of bladder cancer. The anti-tumor effects of mono-treatment with reovirus type 3 Dearing strain (RC402 and RP116) and in combination with interleukin (IL)-18/-21-pretreated eNK cells were investigated on BCC lines (5637, HT-1376, and 253J-BV) using intravesical therapy to simulate in vitro model. RP116 and IL-18/-21-pretreated eNK cells exhibited effective cytotoxicity against grade 1 carcinoma (5637 cells) when used alone, but not against HT-1376 (grade 2 carcinoma) and 253J-BV cells (derived from a metastatic site). Notably, combining RP116 with IL-18/-21-pretreated eNK cells displayed effective cytotoxicity against both HT-1376 and 253J-BV cells. Our findings underscore the potential of a combination therapy using reoviruses and NK cells as a promising strategy for treating bladder cancer.

Identification of the C1qDC gene family in grass carp (Ctenopharyngodon idellus) and the response of C1qA, C1qB, and C1qC to GCRV infection in vivo and in vitro.

Proteins from the C1q domain-containing (C1qDC) family recognize self-, non-self-, and altered-self ligands and serves as an initiator molecule for the classical complement pathway as well as recognizing immune complexes. In this study, C1qDC gene family members were identified and analyzed in grass carp (Ctenopharyngodon idellus). Members of the C1q subfamily were cloned, and their response to infection with the grass carp virus was investigated. In the grass carp genome, 54 C1qDC genes and 67 isoforms have been identified. Most were located on chromosome 3, with 52 shared zebrafish homologies. Seven substantially differentially expressed C1qDC family genes were identified in the transcriptomes of cytokine-induced killer (CIK) cells infected with grass carp reovirus (GCRV), all of which exhibited sustained upregulation. The opening reading frames of grass carp C1qA, C1qB, and C1qC, belonging to the C1q subfamily, were determined to be 738, 732, and 735 base pairs, encoding 245, 243, and 244 amino acids with molecular weights of 25.81 kDa, 25.63 kDa and 26.16 kDa, respectively. Three genes were detected in the nine collected tissues, and their expression patterns were similar, with the highest expression levels observed in the spleen. In vivo after GCRV infection showed expression trends of C1qA, C1qB, and C1qC in the liver, spleen, and kidney. An N-type pattern in the liver and kidney was characterized by an initial increase followed by a decrease, with the highest expression occurring during the recovering period, and a V-type pattern in the spleen with the lowest expression levels during the death period. In vitro, after GCRV infection showed expression trends of C1qA, C1qB, and C1qC, and this gradually increased within the first 24 h, with a notable increase observed at the 24 h time point. After CIK cells incubation with purified recombinant proteins, rC1qA, rC1qB, and rC1qC for 3 h, followed by GCRV inoculation, the GCRV replication indicated that rC1qC exerted a substantial inhibitory effect on viral replication in CIK cells after 24 h of GCRV inoculation. These findings offer valuable insights into the structure, evolution, and function of the C1qDC family genes and provide a foundational understanding of the immune function of C1q in grass carp.

Black carp ATG16L1 negatively regulates STING-mediated antiviral innate immune response.

The precise control of interferon (IFN) production is indispensable for the host to eliminate invading viruses and maintain a homeostatic state. In mammals, stimulator of interferon genes (STING) is a prominent adaptor involved in antiviral immune signaling pathways. However, the regulatory mechanism of piscine STING has not been thoroughly investigated. Here, we report that autophagy related 16 like 1 (bcATG16L1) of black carp (Mylopharyngodon piceus) is a negative regulator in black carp STING (bcSTING)-mediated signaling pathway. Initially, we substantiated that knockdown of bcATG16L1 increased the transcription of IFN and ISGs and enhanced the antiviral activity of the host cells. Subsequently, we identified that bcATG16L1 inhibited the bcSTING-mediated IFN promoter activation and proved that bcATG16L1 suppressed bcSTING-mediated antiviral ability. Furthermore, we revealed that bcATG16L1 interacted with bcSTING and the two proteins shared a similar subcellular distribution. Mechanically, we found that bcATG16L1 attenuated the oligomerization of bcSTING, which was a key step for bcSTING activation. Taken together, our results indicate that bcATG16L1 interacts with bcSTING, dampens the oligomerization of bcSTING, and negatively regulates bcSTING-mediated antiviral activity.

STAT2 negatively regulates RIG-I in the antiviral innate immunity of black carp.

The signal transducer and activator of transcription 2 (STAT2), a downstream factor of type I interferons (IFNs), is a key component of the cellular antiviral immunity response. However, the role of STAT2 in the upstream of IFN signaling, such as the regulation of pattern recognition receptors (PRRs), remains unknown. In this study, STAT2 homologue of black carp (Mylopharyngodon piceus) has been cloned and characterized. The open reading frame (ORF) of bcSTAT2 comprises 2523 nucleotides and encodes 841 amino acids, which presents the conserved structure to that of mammalian STAT2. The dual-luciferase reporter assay and the plaque assay showed that bcSTAT2 possessed certain IFN-inducing ability and antiviral ability against both spring viremia of carp virus (SVCV) and grass carp reovirus (GCRV). Interestingly, we detected the association between bcSTAT2 and bcRIG-I through co-immunoprecipitation (co-IP) assay. Moreover, when bcSTAT2 was co-expressed with bcRIG-I, bcSTAT2 obviously suppressed bcRIG-I-induced IFN expression and antiviral activity. The subsequent co-IP assay and immunoblotting (IB) assay further demonstrated that bcSTAT2 inhibited K63-linked polyubiquitination but not K48-linked polyubiquitination of bcRIG-I, however, did not affect the oligomerization of bcRIG-I. Thus, our data conclude that black carp STAT2 negatively regulates RIG-I through attenuates its K63-linked ubiquitination, which sheds a new light on the regulation of the antiviral innate immunity cascade in vertebrates.

Novel Aquareovirus isolated from channel catfish (Ictalurus punctatus) used in mussel restoration efforts in Wisconsin.

Channel catfish (Ictalurus punctatus) are a food fish extensively reared in aquaculture facilities throughout the world and are also among the most abundant wild catfish species in North America, making them a popular target of anglers. Furthermore, channel catfish are important members of aquatic ecosystems; for example, they serve as a glochidial host for the endangered winged mapleleaf mussel (Quadrula fragosa), making them critical for conserving this species through hatchery-based restoration efforts. During a routine health inspection, a novel aquareovirus was isolated from channel catfish used in mussel propagation efforts at a fish hatchery in Wisconsin. This virus was isolated on brown bullhead cells (ATCC CCL-59) and identified through metagenomic sequencing as a novel member of the family Spinareoviridae, genus Aquareovirus. The virus genome consists of 11 segments, as is typical of the aquareoviruses, with phylogenetic relationships based on RNA-dependent RNA polymerase and major outer capsid protein amino acid sequences showing it to be most closely related to golden shiner virus (aquareovirus C) and aquareovirus C/American grass carp reovirus (aquareovirus G) respectively. The potential of the new virus, which we name genictpun virus 1 (GNIPV-1), to cause disease in channel catfish or other species remains unknown.

Cryo-EM structures of Banna virus in multiple states reveal stepwise detachment of viral spikes.

Banna virus (BAV) is the prototype Seadornavirus, a class of reoviruses for which there has been little structural study. Here, we report atomic cryo-EM structures of three states of BAV virions-surrounded by 120 spikes (full virions), 60 spikes (partial virions), or no spikes (cores). BAV cores are double-layered particles similar to the cores of other non-turreted reoviruses, except for an additional protein component in the outer capsid shell, VP10. VP10 was identified to be a cementing protein that plays a pivotal role in the assembly of BAV virions by directly interacting with VP2 (inner capsid), VP8 (outer capsid), and VP4 (spike). Viral spikes (VP4/VP9 heterohexamers) are situated on top of VP10 molecules in full or partial virions. Asymmetrical electrostatic interactions between VP10 monomers and VP4 trimers are disrupted by high pH treatment, which is thus a simple way to produce BAV cores. Low pH treatment of BAV virions removes only the flexible receptor binding protein VP9 and triggers significant conformational changes in the membrane penetration protein VP4. BAV virions adopt distinct spatial organization of their surface proteins compared with other well-studied reoviruses, suggesting that BAV may have a unique mechanism of penetration of cellular endomembranes.