Muscovy duck reovirus sigmaC protein is atypically encoded by the smallest genome segment

Identification and molecular characterization of novel duck reoviruses in Henan Province, China

Novel Duck reovirus (NDRV) is an ongoing non-enveloped virus with ten double-stranded RNA genome segments that belong to the genus Orthoreovirus, in the family Reoviridae. NDRV-associated spleen swelling, and necrosis disease have caused considerable economic losses to the waterfowl industry worldwide. Since 2017, a significant number of NDRV outbreaks have emerged in China. Herein, we described two cases of duck spleen necrosis disease among ducklings on duck farms in Henan province, central China. Other potential causative agent, including Muscovy duck reovirus (MDRV), Duck hepatitis A virus type 1 (DHAV-1), Duck hepatitis A virus type 3 (DHAV-3), Newcastle disease virus (NDV), and Duck tembusu virus (DTMUV), were excluded by reverse transcription-polymerase chain reaction (RT-PCR), and two NDRV strains, HeNXX-1/2021 and HNJZ-2/2021, were isolated. Sequencing and phylogenetic analysis of the σC genes revealed that both newly identified NDRV isolates were closely related to DRV/SDHZ17/Shandong/2017. The results further showed that Chinese NDRVs had formed two distinct clades, with late 2017 as the turning point, suggesting that Chinese NDRVs have been evolving in different directions. This study identified and genetic characteristics of two NDRV strains in Henan province, China, indicating NDRVs have evolved in different directions in China. This study provides an insight into the ongoing emerged duck spleen necrosis disease and enriches our understanding of the genetic diversity and evolution of NDRVs.

Distinct Whole Transcriptomic Profiles of the Bursa of Fabricius in Muscovy Ducklings Infected by Novel Duck Reovirus with Different Virulence

Novel duck reovirus (NDRV) is a newly identified reovirus that brings about more severe damage on multiple organs and mortality in various species of waterfowl. We previously characterized the transcriptomic profiles responding to NDRV in the bursa of Fabricius of Muscovy ducklings, which is a major immunological organ against virus infection. However, the molecular mechanisms of variant cell responses in the bursa of Fabricius to NDRV with different virulence is unclear. Here, we conducted a whole transcriptomic analysis to study the effects of two strains, HN10 (virulent NDRV) and JDm10 (artificially attenuated NDRV), on the bursa of Fabricius of Muscovy ducklings. We harvested a large number of differentially expressed genes (DEGs) of the bursa of Fabricius specially induced by HN10 and JDm10, and we found that HN10 induced DEGs enriched in differentiation and development in multiple organs beyond JDm10. Moreover, the ceRNA regulatory network also indicated the different connections among mRNA, lncRNA and miRNA. Interestingly, we further noticed that a population of differential expressed miRNA could particularly target to transcripts of HN10 and JDm10. We took miR-24 as an example and observed that miR-24 could reduce the transcription of GLI family zinc finger 3 (Gli3) and membrane-associated guanylate kinase, WW and PDZ domain containing 1 (Magi1) via recognition 3' UTR of these two genes by a dual luciferase reporter gene assay in vitro. However, this effect could be compromised by HN10 infection or the ectopic over-expression of the putative miR-24 targeting regions in L1 and L3 fragments of HN10. Taken together, we examined and proposed a novel regulatory competitive mechanism between transcripts of NDRV and Muscovy ducklings for miRNA. These findings may advance the understanding of the molecular pathogenesis of NDRV in Muscovy ducklings, and help provide the potential targets for vaccine and drug development against NDRV.

The phosphoproteomic responses of duck (Cairna moschata) to classical/novel duck reovirus infections in the spleen tissue

Duck reovirus (DRV) is a fatal member of the genus Orthoreovirus in the family Reoviridae. The disease caused by DRV leads to huge economic losses to the duck industry. Post-translational modification is an efficient strategy to enhance the immune responses to virus infection. However, the roles of protein phosphorylation in the responses of ducklings to Classic/Novel DRV (C/NDRV) infections are largely unknown. Using a high-resolution LC–MS/MS integrated to highly sensitive immune-affinity antibody method, phosphoproteomes of Cairna moschata spleen tissues under the C/NDRV infections were analyzed, producing a total of 8,504 phosphorylation sites on 2,853 proteins. After normalization with proteomic data, 392 sites on 288 proteins and 484 sites on 342 proteins were significantly changed under the C/NDRV infections, respectively. To characterize the differentially phosphorylated proteins (DPPs), a systematic bioinformatics analyses including Gene Ontology annotation, domain annotation, subcellular localization, and Kyoto Encyclopedia of Genes and Genomes pathway annotation were performed. Two important serine protease system-related proteins, coagulation factor X and fibrinogen α-chain, were identified as phosphorylated proteins, suggesting an involvement of blood coagulation under the C/NDRV infections. Furthermore, 16 proteins involving the intracellular signaling pathways of pattern-recognition receptors were identified as phosphorylated proteins. Changes in the phosphorylation levels of MyD88, NF-κB, RIP1, MDA5 and IRF7 suggested a crucial role of protein phosphorylation in host immune responses of C. moschata. Our study provides new insights into the responses of ducklings to the C/NDRV infections at PTM level.

A TaqMan-based real-time PCR assay for specific detection of novel duck reovirus in China

BACKGROUND

In China, Newly emerging duck reovirus (NDRV) variants have been causing major disease problems in cherry valley ducks. NDRV has the potential to cause high morbidity and 5-50% mortality rates. Severe hemorrhagic-necrosis in the liver and spleen were commonly seen in NDRV affected ducks. The availability of upgraded methods for rapid diagnosis of newly emerging DRV variants is crucial for successful DRV infection control and prevention.

RESULTS

In this study, we present a TaqMan-based real-time PCR assay (RT-qPCR) for the detection of NDRV infection. Using the conserved regions within the NDRV genome, we designed the specific primers and probe. The lower limit of detection for NDRV infection was 10 copies/μL (Ct values: 38.3) after the optimization of the RT-qPCR conditions. By cross-checking with other duck viral pathogens, no cross-reactivity was observed confirming the assay was highly specific for the detection of NDRV. Reproducibility of the RT-qPCR was confirmed by intra- and inter-assay variability was less than 2.91%(Intra-assay variability of Ct values: 0.07-1.48%; Interassay variability of Ct values: 0.49-2.91%). This RT-qPCR and conventional PCR (cPCR) detected one hundred and twenty samples of NDRV infection from different regions. The result shows that the positive rates were 94.17 and 84.17% respectively. The detection rate of RT-qPCR rapid detection assay was 10% higher than that of the cPCR method.

CONCLUSION

This research developed a highly sensitive, specific, reproducible and versatile of RT-qPCR for quantitatively detecting NDRV. It can be used to study the pathogenesis and epidemiology investigation of NDRV.

Polycistronic Genome Segment Evolution and Gain and Loss of FAST Protein Function during Fusogenic Orthoreovirus Speciation

The Reoviridae family is the only non-enveloped virus family with members that use syncytium formation to promote cell–cell virus transmission. Syncytiogenesis is mediated by a fusion-associated small transmembrane (FAST) protein, a novel family of viral membrane fusion proteins. Previous evidence suggested the fusogenic reoviruses arose from an ancestral non-fusogenic virus, with the preponderance of fusogenic species suggesting positive evolutionary pressure to acquire and maintain the fusion phenotype. New phylogenetic analyses that included the atypical waterfowl subgroup of avian reoviruses and recently identified new orthoreovirus species indicate a more complex relationship between reovirus speciation and fusogenic capacity, with numerous predicted internal indels and 5’-terminal extensions driving the evolution of the orthoreovirus’ polycistronic genome segments and their encoded FAST and fiber proteins. These inferred recombination events generated bi- and tricistronic genome segments with diverse gene constellations, they occurred pre- and post-orthoreovirus speciation, and they directly contributed to the evolution of the four extant orthoreovirus FAST proteins by driving both the gain and loss of fusion capability. We further show that two distinct post-speciation genetic events led to the loss of fusion in the waterfowl isolates of avian reovirus, a recombination event that replaced the p10 FAST protein with a heterologous, non-fusogenic protein and point substitutions in a conserved motif that destroyed the p10 assembly into multimeric fusion platforms.

The genomic constellation of a novel duck reovirus strain associated with hemorrhagic necrotizing hepatitis and splenitis in Muscovy ducklings in Fujian, China

The complete sequence of a reovirus, strain NP03 associated with necrotic focus formation in the liver and spleen of Muscovy ducklings in Fujian Province, China in 2009, was determined and compared with sequences of other waterfowl and chicken-origin avian reoviruses (ARVs). Sequencing of the complete genomes of strain NP03 showed that they consisted of 23,418 bp and were divided into 10 segments, ranging from 1191 bp (S4) to 3959 bp (L1) in length, and all segments contained conserved sequences in the 5' non-coding region (GCUUUU) and 3' non-coding region (UCAUC). Pairwise sequence comparisons demonstrated that NP03 strain showed the highest similarity with novel waterfowl origin reoviruses (WRVs). The genome analysis revealed that the S1 segment of novel WRV is a tricistronic gene, encoding the overlapping open reading frames (ORFs) for p10, p18, and σC, similar to the ARV S1 gene, but distinct from classical WRV S4 genome segment, which contained two overlapping ORFs encoding p10 and σC. Phylogenetic analyses of the nucleotide sequences of all 10 segments revealed that NP03 strain was clustered together with other novel WRVs and were distinct from classical WRVs and chicken-origin ARVs. The analyses also showed possible intra-segmental reassortment events in the segments encoding λA, λB, μB, μNS, σA, and σNS between novel and classical WRVs. Potential recombination events detection in segment L1 suggests that NP03 strain may be recombinants of novel WRVs. Based on our genetic analyses, multiple reassortment events, intra-segmental recombination, and accumulation of point mutations have possibly contributed to the emergence of this novel genotype of WRV, identified in China.

The diagnosis and successful replication of a clinical case of Duck Spleen Necrosis Disease: An experimental co-infection of an emerging unique reovirus and Salmonella indiana reveals the roles of each of the pathogens

Duck spleen necrosis disease (DSND) is an emerging infectious disease that causes significant economic loss in the duck industry. In 2018, a duck reovirus (named DRV/GX-Y7) and Salmonella indiana were both isolated from the spleens and livers of diseased ducks with DSND in China. The DRV/GX-Y7 strain could propagate in the Vero, LMH, DF-1 and DEF cells with obvious cytopathic effects. The genome of DRV/GX-Y7 was 23,418 bp in length, contained 10 dsRNA segments, ranging from 3959 nt (L1) to 1191 nt (S4). The phylogenetic analysis showed that the DRV/GX-Y7 strain was in the same branch with the new waterfowl-origin reovirus cluster, but was obviously far distant from the clusters of other previous waterfowl-origin reoviruses Muscovy duck reovirus (MDRV) and goose-origin reovirus (GRV), broiler/layer-origin reovirus (ARV) and turkey-origin reovirus (TRV). The RDP and SimPlot program analysis revealed that there were two potential genetic reassortment events in the M2 and S1 segments of the genome. In order to have a clear insight into the pathogenic mechanism of DRV/GX-Y7 and S. Indiana in clinical DSND, an infection experiment was further conducted by challenging commercial ducklings with the two isolates individually and with both. The results showed that DRV/GX-Y7 produced severe hemorrhagic and/or necrotic lesions in the immune organs (thymus, spleen, and bursae) of experimentally infected ducklings. And, that the co-infection of DRV/GX-Y7 and S. Indiana could greatly enhance the pathogenesis by increasing the morbidity and mortality in ducklings whose clinical symptoms and lesions were similar to the natural clinical DSND cases. In summary, the results suggested that the pathogen causing duck spleen necrosis was an emerging unique genetic reassortment strain of duck Orthoreovirus that was significantly different from any previously reported waterfowl-derived Orthoreovirus and the co-infection with the Salmonella isolate could increase the severity of the disease.

Characterization of Monoclonal Antibodies against σA Protein and Cross-Reactive Epitope Identification and Application for Detection of Duck and Chicken Reovirus Infections

Although σA is an important major core protein of duck reovirus (DRV), the B-cell epitopes of this protein remain unknown to reseacrhers. Six monoclonal antibodies (MAbs) (1A7, 3F4, 5D2, 4E2, 3C7, and 2B7) were developed by using prokaryotic-expressed recombinant His-σA protein. Five of six MAbs (1A7, 3F4, 4E2, 3C7, and 2B7) reacted with His-σA protein in a conformation-independent manner, while 5D2 reacted with σA in a conformation-dependent manner. Immunofluorescence assays showed that the MAbs could specifically bind to DRV infected BHK-21 cells. The MAbs were delineated as three groups by a competitive binding assay. By using 12-mer peptide phage display and mutagenesis, MAb 4E2 was identified to recognize minimal epitope ⁵⁶EAPYPG⁶¹ and MAb 1A7 recognize ³⁴¹WVV/MAGLI/V³⁴⁷, residues ³⁴¹V/M and ³⁴⁷I/V are replaceable. Dot blotting and sequence analysis confirmed that EAPYPG and WVV/MAGLI/V are cross-reactive epitopes in both DRV and avian reovirus (ARV). An enzyme-linked immunosorbent assay (ELISA) based on two expressed EAPYPG and WVVAGLI as antigen demonstrated its diagnostic potential by specific reacting with serum samples from DRV- or ARV-infected birds. Based on these observations, an epitope-based ELISA could be potentially used for DRV or ARV surveillance. These findings provide insights into the organization of epitopes on σA protein that might be valuable for the development of epitope-based serological diagnostic tests for DRV and ARV infection.

Fusogenic Reoviruses and Their Fusion-Associated Small Transmembrane (FAST) Proteins

With no limiting membrane surrounding virions, nonenveloped viruses have no need for membrane fusion to gain access to intracellular replication compartments. Consequently, nonenveloped viruses do not encode membrane fusion proteins. The only exception to this dogma is the fusogenic reoviruses that encode fusion-associated small transmembrane (FAST) proteins that induce syncytium formation. FAST proteins are the smallest viral membrane fusion proteins and, unlike their enveloped virus counterparts, are nonstructural proteins that evolved specifically to induce cell-to-cell, not virus-cell, membrane fusion. This distinct evolutionary imperative is reflected in structural and functional features that distinguish this singular family of viral fusogens from all other protein fusogens. These rudimentary fusogens comprise specific combinations of different membrane effector motifs assembled into small, modular membrane fusogens. FAST proteins offer a minimalist model to better understand the ubiquitous process of protein-mediated membrane fusion and to reveal novel mechanisms of nonenveloped virus dissemination that contribute to virulence.

Isolation and characterization of a variant duck orthoreovirus causing spleen necrosis in Peking ducks, China

Since December 2017, an infectious disease has caused economic hardship for duck farms and breeding ducks in many regions of China. This disease characterized by spleen necrosis and swelling, is due to a variant strain of duck orthoreovirus (DRV) (Duck/N-DRV-XT18/China/2018), which we isolated from the spleen of diseased ducks. After isolating the virus, we used next-generation sequencing technology to determine the entire genomic of the virus. Our phylogenetic analysis of 10 genomic segments showed that the N-DRV-XT18 strain is closely related to orthoreovirus isolates derived from ducks and geese, with nucleotide sequence identities for 10 genomic fragments ranging between 49.8% and 99.3%. In contract, the nucleotide sequence of N-DRV-XT18 genomic fragments are only 38.6% to 78.8% similar to the chicken orthoreovirus isolate. Therefore, we determined that this pathogen, causing duck spleen necrosis, is a new variant of a duck orthoreovirus that is significantly different from any previously reported waterfowl-derived othoreovirus.

Cdc20 and molecular chaperone CCT2 and CCT5 are required for the Muscovy duck reovirus p10.8-induced cell cycle arrest and apoptosis

This study demonstrates that the Muscovy duck reovirus (MDRV) p10.8 protein is one of many viral non-structural proteins that induces both cell cycle arrest and apoptosis. The p10.8 but not σC is a nuclear targeting protein that shuttles between the nucleus and the cytoplasm. Our results reveal that p10.8-induced apoptosis in cultured cells occurs by the nucleoporin Tpr/p53-dependent and Fas/caspase 8-mediated pathways. Furthermore, a compelling finding from this study is that the p10.8 and σC proteins of MDRV facilitate CDK2 and CDK4 degradation via the ubiquitin-proteasome pathway. We found that depletion of Cdc20 reversed the p10.8- and σC- mediated CDK4 degradation and p10.8-induced apoptosis, suggesting that Cdc20 plays a critical role in modulating p10.8-mediated cell cycle and apoptosis. Furthermore, we found that depletion of chaperonin-containing tailless complex polypeptide 1 (CCT) 2 and CCT5 reduced the level of Cdc20 and reversed the p10.8- and σC-mediated CDK4 degradation and p10.8-induced apoptosis, indicating that molecular chaperone CCT2 and CCT5 are required for stabilization of Ccd20 for mediating both cell cycle arrest and apoptosis. This study provides mechanistic insights into how p10.8 induces both cell cycle arrest and apoptosis.

Development of a live attenuated vaccine against Muscovy duck reovirus infection

The Muscovy duck reovirus (MDRV) is a highly pathogenic virus that causes substantial economic losses in the Muscovy duck industry. While MDRV poses a significant threat to Muscovy ducklings, no vaccine candidates are available to date to alleviate MDRV infection throughout the world. The present study presents efforts toward establishing an attenuated vaccine for MDRV. For this purpose, a live attenuated vaccine strain named CA was obtained via alternate propagation of the MDRV isolate MW9710 in both Muscovy duck embryo fibroblasts (MDEFs) and chicken embryo fibroblasts (CEFs) for 90 passages. The CA strain achieved an adaptive growth capacity in CEFs with a viral titer that ranged between 10^5.0-10^5.5 TCID₅₀/100 μL and lost its pathogenicity in 1-day-old Muscovy ducklings. Compared to the parent strain MW9710, the CA strain has 42 scattered amino acid substitutions, most of which are located in the λB, λC, μB, σB, and σC protein. The CA strain maintained its attenuation and showed no gene mutation or virulence reversion after back propagation into 1-day-old ducklings for five rounds. The minimum protective dose was calculated to be 300 TCID₅₀ of the CA strain. Furthermore, a single dose of CA vaccine protected immunized ducklings against lethal challenge by the virulent MDRV strain MW9710 and significantly decreased viral loads. In summary, the CA strain exhibited striking genetic stability, excellent safety, and effective immunogenicity. This CA strain of MDRV is a promising vaccine candidate for the prevention and control of MDRV infection.

Comparative proteomic analysis revealed complex responses to classical/novel duck reovirus infections in the spleen tissue of Cairna moschata

Duck reovirus (DRV), a member of the genus Orthoreovirus in the family Reoviridae, was first isolated from Muscovy ducks. The disease associated with DRV causes great economic losses to the duck industry. However, the responses of duck (Cairna moschata) to the classical/novel DRV (C/NDRV) infections are largely unknown. To reveal the relationship of pathogenesis and immune response, the proteomes of duck spleen cells under the control and C/NDRV infections were compared. In total, 5986 proteins were identified, of which 5389 proteins were quantified. The different accumulated proteins (DAPs) under the C/NDRV infections showed displayed various biological functions and diverse subcellular localizations. The proteins related to the serine protease system were siginificantly changed, suggesting that the activated serine protease system may play an important role under the C/NDRV infections. Furthermore, the differences in the responses to the C/NRDV infections between the duck liver and spleen tissues were compared. Only a small number of common DAPs were identified in both liver and spleen tissues, suggesting diversified pattern involved in the responses to the C/NRDV infections. However, the changes in the proteins involved in the serine protease systems were similar in both liver and spleen cells. Our data may give a comprehensive resource for investigating the responses to C/NDRV infections in ducks. SIGNIFICANCE: A newly developed MS/MS-based method involving isotopomer labels and 'tandem mass' has been applied to protein accurate quantification in current years. However, no studies on the responses of duck (Cairna moschata) spleen tissue to the classical/novel DRV (C/NDRV) infections have been performed. As a continued study of our previous report on the responses of duck liver tissue to the C/NDRV infections, the current study further compared the differences in the responses to the C/NRDV infections between the duck liver and spleen tissues. Our results will provide an opportunity to reveal the relationship of pathogenesis and immune response and basic information on the pathogenicity of C/NDRV in ducks.

Analysis of differentially expressed proteins in Muscovy duck embryo fibroblasts infected with virulent and attenuated Muscovy duck reovirus by two-dimensional polyacrylamide gel electrophoresis

Muscovy duck reovirus (MDRV) belongs to the Orthoreovirus genus of the Reoviridae family, which is a significant poultry pathogen leading to high morbidity and mortality in ducklings. However, the pathogenesis of the virus is not well understood. In the present study, two-dimensional (2D) polyacrylamide gel electrophoresis (PAGE) combined with LC-MS-MS was used to identify differentially expressed proteins between Muscovy duck embryo fibroblasts (MDEF) infected with virulent (MV9710 strain) and attenuated (CA strain) MDRV and non-infected MDEFs. A total of 115 abundant protein spots were identified. Of these, 59 of differentially expressed proteins were detected, with functions in metabolism and utilization of carbohydrates and nucleotides, anti-stress, and regulation of immune and cellular process. GO analysis of the identified proteins showed that they belonged to the classes molecular function (141 proteins), cellular component (62 proteins), and biological process (146 proteins). The results were validated by qRT-PCR, which suggests that the analysis method of 2D PAGE combined with LC-MS-MS used in this study is reliable. This study lays a foundation for further investigation of the biology of MDRV infection in MDEF.

Preparation and evaluation of goose reovirus inactivated vaccine

Background

Infection with Goose Reovirus (GRV) can cause serious economic losses in the goose breeding industry. In this study, the GRV allantoic fluid was concentrated and used as an antigen in a formalin-inactivated oil-emulsion vaccine.

Results

When 6 day-old geese were inoculated, antibodies against GRV became detectable at 6 days post-vaccination, their concentration peaked at 3 weeks. These antibodies were maintained for longer than 2 weeks. As the most susceptible age for GRV infection is birds under 2 weeks of age this vaccine should provide adequate cover for the most at risk birds. When geese were exposed to reovirus at different time intervals after immunization, the data revealed that the vaccine can provide a protection rate of 80%. The developed vaccine has good stability and could be stored at 4 °C for at least 12 months.

Conclusion

These results indicate that the developed GRV vaccine is safe, effectively absorbed, efficacious in inducing a rapid immune response, and effective in controlling GRV infection. Our results should be useful for the application of vaccines for controlling GRV in different goose flocks.

Electronic supplementary material

The online version of this article (doi:10.1186/s12917-017-1134-0) contains supplementary material, which is available to authorized users.

Muscovy duck reovirus σNS protein triggers autophagy enhancing virus replication

Background

Muscovy duck reovirus (MDRV) causes high morbidity and mortality in Muscovy ducklings at 10 days old and can persist in an infected flock until the ducklings of 6 weeks old. It shares common physicochemical properties with avian reovirus (ARV) and differs in coding assignment and pathogenicity. The ARV p17 protein has been shown to trigger autophagy via activation multiple signaling pathways, which benefits virus replication. Since MDRV lacks the p17 protein, whether and how MDRV induces autophagy remains unknown. The aim of this study was to explore whether MDRV induces autophagy and which viral proteins are involved in MDRV-induced autophagy.

Methods

The autophagosome-like structures in MDRV-infected cells was observed under transmission electron microscopy. MDRV-induced autophagy was examined by analyzing the LC3-II level and phosphorylated form of mammalian target of rapamycin (mTOR) by Western blot assays. The effects of 3-methyladenine, rapamycin, chloroquine on viral yields were measured with quantitative(q) real-time reverse transcription (RT)-polymerase chain reaction (PCR) and 50% tissue culture infective dose (TCID₅₀) assays, respectively. Additionally, to determine which viral protein is responsible for MDRV-induced autophagy, both p10.8- and σNS-encoding genes of MDRV were cloned into the pCI-neo-flag vector and transfected into DF-1 cells for detection of LC3-II.

Results

The typical double-membrane vesicles containing cytoplasmic inclusions were visible in MDRV-infected immortalized chicken embryo fibroblast (DF-1) cells under transmission electron microscopy. Both primary Muscovy duck embryo fibroblasts (MDEF) and DF-1 cells infected with MDRV exhibited a significant increased levels of LC3-II accompanied with downregulation of phosphorylated form of mTOR, further confirming that MDRV is capable of inducing autophagy. Autophagy could be suppressed by 3-methylademine and induced by rapamycin and chloroquine. Furthermore, we found that σNS induces an increased levels of LC3-II, suggesting that the MDRV σNS protein is one of viral proteins involved in induction of autophagy. Both qRT-PCR and TCID₅₀ assays showed that virus yield was increased in rapamycin treated DF-1 cells following MDRV infection. Conversely, when infected cells were pretreated with chloroquine, virus yield was decreased.

Conclusions

The MDRV σNS nonstructural protein is responsible for MDRV-induced autophagy and benefits virus replication.

Development and application of an indirect ELISA for the detection of antibodies to novel duck reovirus

A novel duck reovirus (N-DRV) disease emerged in China in 2000 and it has become an epidemic genotype. A test for detection of virus-specific antibodies in serum samples would be useful for epidemiological investigations. Currently, Currently, serological assays for N-DRV diagnosis are not available. A test for detection of virus-specific antibodies in serum samples would be useful for epidemiological investigations. In this study, a highly sensitive and specific indirect enzyme-linked immunosorbent assay (ELISA) for the detection of antibodies to N-DRV was developed. The outer capsid (σC) of N-DRV was cloned and expressed in Escherichia coli as a coating antigen. The antigen concentration and serum dilution were optimized using a checkerboard titration. Furthermore, the specificity of σC-ELISA assay was confirmed by cross checking with other duck viral pathogens. In comparison with the western blot, the sensitivity and specificity of the σC-ELISA was 92.6% and 88.9%, respectively, and agreement of two tests was excellent with κ value of 0.786 (p < 0.05). A serological survey was performed using the assay on serum samples from different age and species of duck flocks in the Zhejiang and Jiangsu Province, China. The seropositive rate of the 1209 serum samples was 57.7%. In conclusion, the developed σC-ELISA assay is a very specific and sensitive test that will be useful for large-scale serological survey in N-DRV infection and monitoring antibodies titers against N-DRV.

Molecular characterization of a novel reovirus isolated from Pekin ducklings in China

The complete genome sequence of a novel duck orthoreovirus, designated DRV strain TH11(DRV-TH11), was determined and characterized. The DRV-TH11 genome is comprised of 23,417 bp and its genome organization is more similar to that of avian orthoreoviruses (ARVs) of chicken origin than other reoviruses. The results of comparative sequence analysis and dendrograms based on the µB- and σC-encoding genes indicated that TH11 may be derived from the reassortment of ARVs and classic Muscovy duck reovirus (MDRV). A possible recombinant event was identified using the SimPlot program, and it occurred in the M2 segment. The results indicated that reassortment and mutation play a role in the evolution of duck reovirus.

Muscovy duck reovirus p10.8 protein localizes to the nucleus via a nonconventional nuclear localization signal

Background

It was previously report that the first open reading frame of Muscovy duck reocvirus S4 gene encodes a 95-amino-acid protein, designed p10.8, which has no sequence similarity to other known proteins. Its amino acid sequence offers no clues about its function.

Results

Subcellular localization and nuclear import signal of p10.8 were characterized. We found that p10.8 protein localizes to the nucleus of infected and transfected cells, suggesting that p10.8 nuclear localization is not facilitated by viral infection or any other viral protein. A functional non-canonical nuclear localization signal (NLS) for p10.8 was identified and mapped to N-terminus residues 1–40. The NLS has the ability to retarget a large cytoplasmic protein to the nucleus.

Conclusions

p10.8 imported into the nucleus might via a nonconventional signal nuclear signal.

Antigenic analysis of monoclonal antibodies against different epitopes of σB protein of avian reovirus

BACKGROUND

Avian reovirus (ARV) causes arthritis, tenosynovitis, runting-stunting syndrome (RSS), malabsorption syndrome (MAS) and immunosuppression in chickens. σB is one of the major structural proteins of ARV, which is able to induce group-specific antibodies against the virus.

METHODS AND RESULTS

The present study described the identification of two linear B-cell epitopes in ARV σB through expressing a set of partially overlapping and consecutive truncated peptides spanning σB screened with two monoclonal antibodies (mAbs) 1F4 and 1H3-1.The data indicated that (21)KTPACW(26) (epitope A) and (32)WDTVTFH(38) (epitope B) were minimal determinants of the linear B cell epitopes. Antibodies present in the serum of ARV-positive chickens recognized the minimal linear epitopes in Western blot analyses. By sequence alignment analysis, we determined that the epitopes A and B were not conserved among ARV, duck reovirus (DRV) and turkey reovirus (TRV) strains. Western blot assays, confirmed that epitopes A and B were ARV-specific epitopes, and they could not react with the corresponding peptides of DRV and TRV.

CONCLUSIONS AND SIGNIFICANCE

We identified (21)KTPACW(26) and (32)WDTVTFH(38) as σB -specific epitopes recognized by mAbs 1F4 and 1H3-1, respectively. The results in this study may have potential applications in development of diagnostic techniques and epitope-based marker vaccines against ARV groups.

Isolation and genomic characterization of a classical Muscovy duck reovirus isolated in Zhejiang, China

A classical Muscovy reovirus was isolated from a sick Muscovy duck with white necrotic foci in its liver in Zhejiang, China, in 2000. This classical reovirus was propagated in a chicken fibroblast cell line (DF-1) with obvious cytopathic effects. Its genome was 22,967 bp in length, with approximately 51.41% G+C content and 10 dsRNA segments encoding 11 proteins, which formed a 3/3/4 electrophoretic PAGE profile pattern. The length of the genomic segments was similar to those of avian orthoreoviruses (ARV and N-MDRV), ranging from 3959 nt (L1) to 1191nt (S4). All of the segments have the conserved terminal sequences 5'-GCUUUU--UUCAUC-3', and with the exception of the S4 segment, all the genome segments apparently encode one single primary translation product. The genome analysis revealed that the S4 segment of classical MDRV is a bicistronic gene, encoding the overlapping ORFs for p10 and σC but distinct from ARV and N-MDRV/N-GRV, which codes for p10, p18 and σC via the tricistronic S1 segment. A comparative sequence analysis provided evidence indicating extensive sequence divergence between classical MDRV and other avian orthoreoviruses. A phylogenetic analysis based on the RNA-dependent RNA polymerase (RdRp) and the major outer capsid proteins σC was performed. Members of the DRVs in the Avian orthoreovirus species were clustered into two genetic groups (classical MDRV and N-MDRV genotype), and the classical MDRV isolates formed distinct lineages (China and Europe lineages), suggesting that the classical MDRVs isolated in restricted geographical region are evolving by different and independent pathways.

Complete sequence of a reovirus associated with necrotic focus formation in the liver and spleen of Muscovy ducklings

The complete sequence of a reovirus, strain 815-12 associated with necrotic focus formation in the liver and spleen of Muscovy ducklings in China, was determined and compared with sequences of other duck-, goose-, and chicken-origin reoviruses. The 815-12 genome comprised 22,969 bp with 10 dsRNA segments ranging from 1125 bp (S4) to 3958 bp (L1), all of which (except S4) were almost identical in length to the cognate segments of other waterfowl and chicken isolates. Detailed analyses revealed that 815-12 and other waterfowl isolates contained the conserved 3'-terminal pentanucleotide sequence (UCAUC-3') of the orthoreoviruses and 5'-terminal hexanucleotide sequence (5'-GCUUUU) of avian orthoreoviruses (ARVs), and conserved functional motifs previously identified in ARV proteins. Several notable differences, including organization of the polycistronic genome segments and genomic coding assignments of the S segments, existed between viruses represented by 815-12 and the waterfowl reoviruses emerging in China in recent years; the latter was somewhat similar to chicken isolates. Pairwise sequence comparisons demonstrated extensive sequence diversity among the various waterfowl isolates and between waterfowl and chicken isolates. Phylogenetic analyses identified two genetic groups for waterfowl reoviruses, and potential genetic reassortment of segment M2 between waterfowl and chicken reoviruses and segments encoding for λA, λB, μA, μNS and σA between waterfowl reoviruses. Taken together, it was suggested that common designation ARV-Wa should be used to represent ARV isolates from different waterfowl species and that the two ARV-Wa genotypes should be considered as two separate groups distinct from chicken isolates within the species Avian orthoreovirus.

Complete genomic sequence of a new Muscovy duck-origin reovirus from China

The complete genomic sequence of a new Muscovy duck-origin reovirus (N-MDRV), strain J18 from China, was determined. The virus has a tricistronic S1 genome segment that is distinct from the originally described MDRV, which possesses a bicistronic S4 genome segment. Pairwise comparisons and phylogenetic analyses suggest that N-MDRV J18 is a new isolate within the species Avian orthoreovirus.

Antigenic analysis monoclonal antibodies against different epitopes of σB protein of Muscovy duck reovirus

σB is one of the major structural proteins of Muscovy duck reovirus (DRV), which is able to induce protective immune response in target birds. Four anti-DRV σB MAbs were identified belong to two distinct epitopes, designated A (1E5, 4E3, and 5D8) and B (2F7) (Liu et al., 2010). To understand antigenic determinants of the σB protein, a set of 20 (P1-P20), partially overlapping and consecutive peptides spanning σB were expressed and then screened by MAbs. With Western blot and enzyme-linked immunosorbent assay (ELISA), two minimal units of the linear epitopes, 19YIRAPACWD27 (epitope B) and 65TDGVCFPHHK74 (epitope A), were identified within N-terminal region of the σB protein. The epitope B was highly conserved among DRV and avian reovirus (ARV) strains through sequence alignment analysis. Immunofluorescence assays (IFA) and ELISA, confirmed that epitope B is a broad group-specific epitope among DRV and ARV. Epitope A could only react with chicken embyonated fibroblast cells (CEF) infected with DRV, but not ARV. However, both peptides have good immunogenicity and could induce antibodies against DRV in BALB/c mice. This report documents the first identification of σB epitopes in the precise locations. The two probes would be useful in the development of discriminating diagnostic kits for DRV and ARV infection.

Characterization of monoclonal antibodies against Muscovy duck reovirus sigmaB protein

BACKGROUND

The sigmaB protein of Muscovy duck reovirus (DRV), one of the major structural proteins, is able to induce neutralizing antibody in ducks, but the monoclonal antibody (MAb) against sigmaB protein has never been characterized.

RESULTS

Four hybridoma cell lines secreting anti-DRV sigmaB MAbs were obtained, designated 1E5, 2F7, 4E3 and 5D8. Immunoglobulin subclass tests differentiated them as IgG2b (1E5 and 4E3) and IgM (2F7 and 5D8). Dot blot and western blotting assays showed that MAbs reacted with His-sigmaB protein in a conformation-independent manner. Competitive binding assay indicated that the MAbs delineated two epitopes, A and B of sigmaB. Immunofluorescence assay indicated that the four MAbs could specifically bind to Vero cells infected with DRV and sigmaB was distributed diffusely in the cytoplasma of infected cells. MAbs had universal reactivity to all DRVs tested in an antigen-capture enzyme-linked immunosorbent assay.

CONCLUSION

Results of this research provide important information about the four monoclonal antibodies and therefore the MAbs may be useful candidate for the development of a MAb capture ELISA for rapid detection of DRVs. In addition, it showed that the sigmaB protein was located in the cytoplasma of infected cells by immunofluorescence assay with MAbs. Virus isolation and RT-PCR are reliable way for detection of DRV infection, but these procedures are laborious, time consuming, and requiring instruments. These obvious diagnosis problems highlight the ongoing demand of rapid, reproducible, and automatic methods for the sensitive detection of DRV.

Characterization of M-class genome segments of muscovy duck reovirus S14

This report documents the first sequence analysis of the entire M1, M2, and M3 genome segments of the muscovy duck reovirus (DRV) S14. The complete sequence of each of the three M gene segments was determined. The M1 genome segment was 2283 nucleotides in length and was predicted to encode muA protein of 732 residues. The Escherichia coli expressed M1 transcripts generated a 108kDa protein, as expected for muA. A cleavage product of muA, muA1, could be detected by Western blotting with duck anti-reovirus and mouse anti-muA polyclonal serum. muA was distributed diffusely in the cytoplasma and nucleus of transfected Vero cells, which provides evidence that muA might be functional related to the mammalian reovirus (MRV) mu2. The M2 gene was 2155 nucleotides in length and was predicted to encode muB major outer capsid protein of 676 amino acids. The M3 genome segment was 1996 nucleotides in length and was predicted to encode a muNS protein of 635 amino acids. It was unexpectedly found that 5'-termini of the M1 and M2 genes ended with 5'-ACUUUU and 5'-UCUUUU, respectively, instead of 5'-GCUUUU, which is present on most mRNAs of other avian reoviruses (ARV). The UCAUC 3'-terminal sequences of the S14 M1, M2, and M3 genome segments are shared by DRV, ARV, and MRV. Alignment of the DRV muA-, muB-, and muNS-encoding genes with ARV revealed 72.9-73.9%, 67.1-69.6%, and 69.4-70.8% nucleotide identity, respectively. The amino acid sequence homology between DRV and ARV ranged from 85.3 to 86.2% (muA), 75.0 to 76.5% (muB), and 78.4 to 79.8% (muNS). Phylogenetic analyses of the M1, M2, M3, and S-class [Kuntz-Simon, G., Le Gall-Recule, G., de Boisseson, C., Jestin, V., 2002. Muscovy duck reovirus sigmaC protein is a typically encoded by the smallest genome segment. J. Gen. Virol. 83, 1189-1200; Zhang, Y., Liu, M., Hu, Q.L., Ouyang, S.D., Tong, G.Z., 2006a. Characterization of the sigmaC-encoding gene from muscovy duck reovirus. Virus Genes 36, 169-174; Zhang, Y., Liu, M., Ouyan, S.D., Hu, Q.L., Guo, D.C., Han, Z., 2006b. Detection and identification of avian, duck, and goose reoviruses by RT-PCR: goose and duck reoviruses aggregated the same specified genogroup in Orthoreovirus Genus II. Arch. Virol. 151, 1525-1538] genome segments suggests that DRV and ARV share a recent common ancestor and that the two lineages have subsequently undergone host dependent evolution.

Characterization of the σC-encoding Gene from Musocvy Duck Reovirus

The sigmaC-encoding gene of two muscovy duck reovirus (DRV) S14 and C4 strains were cloned and completely sequenced. The open reading frame (ORF) comprised 810 bp and encoded 269 amino acids with a predicated molecular mass of 29.5 kDa. Expressed sigmaC fusion protein in Escherichia coli BL21 strain could be detected by Western blotting under duck anti-reovirus polyclonal serum. There are two large gap insertions at the N-terminal part of the DRV sigmaC when necessary to optimize the alignment of the amino acid sequences of the DRV sigmaC had a heptapeptide repeat and leucine zipper patterns structurally related to ARV sigmaC. All DRVs grouped into one specified genogroup within Orthoreoviruses genus subgroup II. The degree of differences between the S14/C4 and ARV was only 23-24%, and 21-22%, respectively, at both the nucleotide and deduced amino acid levels, suggested that DRVs are quite different from ARVs and should give a precise classification for DRVs in Orthoreovirus genus.

Detection and identification of avian, duck, and goose reoviruses by RT-PCR: goose and duck reoviruses are part of the same genogroup in the genus Orthoreovirus

A reverse transcription-polymerase chain reaction (RT-PCR) procedure for the detection of avian, duck, and goose reovirus (ARV, DRV, and GRV) RNA from cell culture supernatant and clinical samples was established. Based on multiple sequence alignment, a pair of degenerate primers was selected and synthesized. The amplified, cloned, and sequenced 598-base-pair products from the sigmaA-encoding gene fragment from 16 isolates (ranging over 30 years) indicated that the primer regions were well conserved. The sensitivity of this method was determined to be 10(-2) PFU. The specificity of the RT-PCR method was determined by testing specimens containing avian influenza A viruses, Newcastle disease virus, and infectious bronchitis virus, all of which yielded negative results with no discernible background. The efficiency of the system for detection of ARV, DRV, and GRV directly in 71/83 clinical samples was confirmed. The nucleotide sequence analysis indicated that DRV and GRV isolated from China in different locales and years were closely related, showing 97.4-100% homology to each other, but with only 86.7-88.5% identity to DRV 89026. The nucleotide and amino acid sequence identities in the amplified sigmaA-encoding gene were 74.2-78.4% and 86.9-92.0%, respectively, between duck/goose and chicken species. Phylogenetic analysis indicated that GRV and DRV aggregated into the same specified genogroup within subgroup II of the genus Orthoreovirus and are more closely related to ARV than to Nelson Bay virus. Overall, this study developed a sensitive and specific technique for the identification ARV, DRV, and GRV, and sequencing analysis has enhanced our understanding of the evolutionary relationship between ARV, DRV, and GRV.

The Goose Reovirus Genome Segment Encoding the Minor Outer Capsid Protein, σ1/σC, is Bicistronic and Shares Structural Similarities with its Counterpart in Muscovy Duck Reovirus

Reoviruses have recently been shown to be associated with disease in young geese and to be involved in epizooties of severe outcome in Hungary. To assess the genetic variability among these pathogenic goose reoviruses (GRVs), we sequenced the S4 genome segment of five GRV strains isolated from different diseased flocks. We found that the GRV S4 genome segment, consisting of two partially overlapping open reading frames (ORFs), shares substantial structural similarity with its counterpart in muscovy duck reoviruses (DRVs). ORF1 is predicted to encode a polypeptide highly similar to the p10 polypeptide of DRV, and ORF2 supposedly encodes the minor outer capsid protein, sigma1/sigmaC. In one of the five GRV strains examined, we identified a single uracil base insertion close to the middle of ORF2. This insertion resulted in a frameshift and in concomitant acquisition of a termination codon (UAA) a few codons downstream, apparently causing truncation of the C-terminal part of the protein. The functional consequences of this assumed mutation, which would result in loss of more than a half of the protein, have yet to be determined. Nonetheless, the sequence and structural similarities between the genome segment encoding sigmal/sigmaC in GRVs and DRVs suggest that these viruses belong to a species distinct from other established species within subgroup 2 of orthoreoviruses.

Structure of the carboxy-terminal receptor-binding domain of avian reovirus fibre sigmaC

Avian reovirus fibre, a homo-trimer of the sigmaC protein, is responsible for primary host cell attachment. The protein expressed in bacteria forms elongated fibres comprised of a carboxy-terminal globular head domain and a slender shaft, and partial proteolysis yielded a carboxy-terminal protease-stable domain that was amenable to crystallisation. Here, we show that this fragment retains receptor-binding capability and report its structure, solved using two-wavelength anomalous diffraction and refined using data collected from three different crystal forms at 2.1 angstroms, 2.35 angstroms and 3.0 angstroms resolution. The carboxy-terminal globular domain has a beta-barrel fold with the same overall topology as the mammalian reovirus fibre (sigma1). However, the monomers of the sigmaC trimer show a more splayed-out arrangement than in the sigma1 structure. Also resolved are two triple beta-spiral repeats of the shaft or stalk domain. The presence in the sequence of heptad repeats amino-terminal to these triple beta-spiral repeats suggests that the unresolved portion of the shaft domain contains a triple alpha-helical coiled-coil structure. Implications for the function and stability of the sigmaC protein are discussed.

Reptilian reovirus: a new fusogenic orthoreovirus species

The fusogenic subgroup of orthoreoviruses contains most of the few known examples of non-enveloped viruses capable of inducing syncytium formation. The only unclassified orthoreoviruses at the species level represent several fusogenic reptilian isolates. To clarify the relationship of reptilian reoviruses (RRV) to the existing fusogenic and nonfusogenic orthoreovirus species, we undertook a characterization of a python reovirus isolate. Biochemical, biophysical, and biological analyses confirmed the designation of this reptilian reovirus (RRV) isolate as an unclassified fusogenic orthoreovirus. Sequence analysis revealed that the RRV S1 and S3 genome segments contain a novel conserved 5'-terminal sequence not found in other orthoreovirus species. In addition, the gene arrangement and the coding potential of the bicistronic RRV S1 genome segment differ from that of established orthoreovirus species, encoding a predicted homologue of the reovirus cell attachment protein and a unique 125 residue p14 protein. The RRV S3 genome segment encodes a homologue of the reovirus sigma-class major outer capsid protein, although it is highly diverged from that of other orthoreovirus species (amino acid identities of only 16-25%). Based on sequence analysis, biological properties, and phylogenetic analysis, we propose this python reovirus be designated as the prototype strain of a fifth species of orthoreoviruses, the reptilian reoviruses.