Preliminary study of the UL55 gene based on infectious Chinese virulent duck enteritis virus bacterial artificial chromosome clone

An alpha-herpesvirus employs host HEXIM1 to promote viral transcription

Although it is widely accepted that herpesviruses utilize host RNA polymerase II (RNAPII) to transcribe viral genes, the mechanism of utilization varies significantly among herpesviruses. With the exception of herpes simplex virus 1 (HSV-1) in alpha-herpesviruses, the mechanism by which RNAPII transcribes viral genes in the remaining alpha-herpesviruses has not been reported. In this study, we investigated the transcriptional mechanism of an avian alpha-herpesvirus, Anatid herpesvirus 1 (AnHV-1). We discovered for the first time that hexamethylene-bis-acetamide-inducing protein 1 (HEXIM1), a major inhibitor of positive elongation factor B (P-TEFb), was significantly upregulated during AnHV-1 infection, and its expression was dynamically regulated throughout the progression of the disease. However, the expression level of HEXIM1 remained stable before and after HSV-1 infection. Excessive HEXIM1 assists AnHV-1 in progeny virus production, gene expression, and RNA polymerase II recruitment by promoting the formation of more inactive P-TEFb and the loss of RNAPII S2 phosphorylation. Conversely, the expression of some host survival-related genes, such as SOX8, CDK1, MYC, and ID2, was suppressed by HEXIM1 overexpression. Further investigation revealed that the C-terminus of the AnHV-1 US1 gene is responsible for the upregulation of HEXIM1 by activating its promoter but not by interacting with P-TEFb, which is the mechanism adopted by its homologs, HSV-1 ICP22. Additionally, the virus proliferation deficiency caused by US1 deletion during the early infection stage could be partially rescued by HEXIM1 overexpression, suggesting that HEXIM1 is responsible for AnHV-1 gaining transcription advantages when competing with cells. Taken together, this study revealed a novel HEXIM1-dependent AnHV-1 transcription mechanism, which has not been previously reported in herpesvirus or even DNA virus studies.IMPORTANCEHexamethylene-bis-acetamide-inducing protein 1 (HEXIM1) has been identified as an inhibitor of positive transcriptional elongation factor b associated with cancer, AIDS, myocardial hypertrophy, and inflammation. Surprisingly, no previous reports have explored the role of HEXIM1 in herpesvirus transcription. This study reveals a mechanism distinct from the currently known herpesvirus utilization of RNA polymerase II, highlighting the dependence on high HEXIM1 expression, which may be a previously unrecognized facet of the host shutoff manifested by many DNA viruses. Moreover, this discovery expands the significance of HEXIM1 in pathogen infection. It raises intriguing questions about whether other herpesviruses employ similar mechanisms to manipulate HEXIM1 and if this molecular target can be exploited to limit productive replication. Thus, this discovery not only contributes to our understanding of herpesvirus infection regulation but also holds implications for broader research on other herpesviruses, even DNA viruses.

A Recombinant Duck Plague Virus Containing the ICP27 Deletion Marker Provides Robust Protection in Ducks

Duck plague virus (DPV) is a member of Alphaherpesvirus genus and poses a major threat to waterfowl breeding. Genetic engineered vaccines that are capable of distinguishing naturally infected from vaccine-immunized animals are useful for eradicating duck plague. In this study, reverse genetics was used to develop an ICP27-deficient strain (CHv-ΔICP27), and its potential as a marker vaccination candidate was evaluated. The results showed that the CHv-ΔICP27 generated in this study exhibited good genetic stability in vitro and was highly attenuated both in vivo and in vitro. The level of neutralizing antibody generated by CHv-ΔICP27 was comparable to that induced by a commercial DPV vaccine, suggesting that it could protect ducks from virulent DPV attack. By using molecular identification techniques such as PCR, restriction fragment length polymorphism, immunofluorescence, Western blotting, and others, it is possible to differentiate the CHv-ΔICP27 from wild-type strains. Moreover, ICP27 can also be a potential target for the genetic engineering vaccine development of alphavirus or perhaps the entire herpesvirus family members due to the highly conservative of ICP27 protein in all herpesvirus family members. IMPORTANCE The development of distinguishable marker vaccines from natural infection is a key step toward eradicating duck plague. Here, we generated a recombinant DPV that carries an ICP27 deletion marker that could be easily distinguished from wild-type strain by molecular biological methods. It was highly attenuated in vitro and in vivo and could provide comparable protection to ducks after a single dose of immunizations, as commercial vaccines did. Our findings support the use of the ICP27-deficient virus as a marker vaccine for DPV control and future eradication.

Duck plague virus pUL15 performs a nonspecial cleavage activity through its C terminal nuclease domain in vitro

Duck plague virus (DPV), also known as anatid herpesvirus, is a double-stranded DNA virus and a member of α herpesvirus. DPV pUL15 is a homolog of herpes simplex virus 1 (HSV-1) pUL15, a terminase large subunit, and plays a key role in the cleavage and packaging of the viral concatemeric genome. However, the sequence similarity between DPV pUL15 and its homologs is low, and it is not sure if DPV pUL15 has the potential to cleave the concatemeric genome as same as its homologs. Here, we expressed the C terminal domain of DPV pUL15 to explore the nuclease function of DPV pUL15. The main results showed that (Ⅰ) DPV pUL15 C-terminal domain possesses nonspecific nuclease activity and lacks the DNA binding ability. (Ⅱ) DPV pUL15 nuclease activity needs to coordinate with divalent metal ions and tends to be more active at high temperatures. (Ⅲ) Even though the structure of DPV pUL15 nuclease domain is relatively conserved, the mutations of conserved amino acids on the nuclease domain do not significantly inhibit the nuclease activity.

BX795, a kinase inhibitor, inhibit duck plague virus infection via targeting US3 kinase

Duck plague virus (DPV) is a typical DNA virus of waterfowl, it causes huge economic losses to the duck industry due to the higher mortality and lower egg production. The disease is one of the frequent epidemics and outbreaks on duck farms because present vaccines could not provide complete immunity and there are no specific antiviral drugs available. Therefore, the development of antiviral drugs is urgently needed. In this study, we evaluated the antiviral activity of BX795, a specific kinase inhibitor of 3-phosphoinositide-dependent kinase 1 (PDK1), protein kinase B (AKT) and Tank binding kinase 1 (TBK1), against DPV in different duck cells. Our study demonstrated that BX795 reveals prominent antiviral activity in a dose-dependent manner in different types of duck cells. Time-addition and antiviral duration analysis uncovered that BX795 inhibits viral infection therapeutically and its antiviral activity lasts longer than 96 h. Further studies have shown that BX795 prevents cell-to-cell spread of the DPV rather than affects other stage of viral life cycle. Mechanistically, BX795 can inhibit DPV US3 kinase activity, reduce the phosphorylation of US3 substrates, and prevent the interaction between US3 and UL47. Taking together, our study demonstrated BX795, which disrupts the viral kinase activity, is a candidate antiviral agent for DPV.

Characterization of a Unique Novel LORF3 Protein of Duck Plague Virus and Its Potential Pathogenesis

Duck plague virus (DPV) is a high-morbidity fowl alphaherpesvirus that causes septicemic lesions in various organs. Most DPV genes are conserved among herpesviruses, while a few are specific to fowl herpesviruses, including the LORF3 gene, for which there is currently no literature describing its biological properties and functions. This study first addressed whether the LORF3 protein is expressed by making specific polyclonal antibodies. We could demonstrate that DPV LORF3 is an early gene and encodes a protein involved in virion assembly, mainly localized in the nucleus of DPV-infected DEF cells. To investigate the role of this novel LORF3 protein in DPV pathogenesis, we generated a recombinant virus that lacks expression of the LORF3 protein. Our data revealed that the LORF3 protein is not essential for viral replication but contributes to DPV replication in vitro and in vivo and promotes duck plague disease morbidity and mortality. Interestingly, deletion of the LORF3 protein abolished thymus atrophy in DPV-vaccinated ducks. In conclusion, this study revealed the expression of avian herpesviruses-specific genes and unraveled the role of the early protein LORF3 in the pathogenesis of DPV. IMPORTANCE DPV is a highly lethal alphaherpesvirus that causes duck plague in birds of the order Anseriformes. The virus has caused huge economic losses to the poultry industry due to high morbidity and mortality and the cost of vaccination. DPV encodes 78 open reading frames (ORFs), and these genes are involved in various processes of the viral life cycle. Functional characterization of DPV genes is important for understanding the complex viral life cycle and DPV pathogenesis. Here, we identified a novel protein encoded by LORF3, and our data suggest that the LORF3 protein is involved in the occurrence and development of duck plague.

Deletion of Double Copies of the US1 Gene Reduces the Infectivity of Recombinant Duck Plague Virus In Vitro and In Vivo

Duck plague caused by duck plague virus (DPV) is one of the main diseases that seriously endangers the production of waterfowl. DPV possesses a large genome consisting of 78 open reading frames (ORFs), and understanding the function and mechanism of each encoded protein in viral replication and pathogenesis is the key to controlling duck plague outbreaks. US1 is one of the two genes located in the repeat regions of the DPV genome, but the function of its encoded protein in DPV replication and pathogenesis remains unclear. Previous studies found that the US1 gene or its homologs exist in almost all alphaherpesviruses, but the loci, functions, and pathogenesis of their encoded proteins vary among different viruses. Here, we aimed to define the roles of US1 genes in DPV infection and pathogenesis by generating a double US1 gene deletion mutant and its revertant without any mini-F cassette retention. In vitro and in vivo studies found that deletion of both copies of the US1 gene significantly impaired the replication, gene expression, and virulence of DPV, which could represent a potential candidate vaccine strain for the prevention of duck plague. IMPORTANCE Duck plague virus contains nearly 80 genes, but the functions and mechanisms of most of the genes have not yet been elucidated, including those of the newly identified immediate early gene US1. Here, we found that US1 deletion reduces viral gene expression, replication, and virus production both in vitro and in vivo. This insight defines a fundamental role of the US1 gene in DPV infection and indicates its involvement in DPV transcription. These results provide clues for the study of the pathogenesis of the US1 gene and the development of attenuated vaccines targeting this gene.

Evaluation of safety and immunogenicity of duck-plague virus gC/gE double gene deletion

Duck plague caused by duck plague virus (DPV) is a highly contagious disease that can cause serious morbidity and death in waterfowl such as ducks and geese, and bring huge economic losses to the duck industry. In this study, on the basis of the duck plague virus gC gene deletion strain CHv-ΔgC, based on the duck plague virus bacterial artificial chromosome (BAC) platform in our laboratory, the gE gene was knocked out using the traceless deletion technology to obtain gC/gE double gene deletion candidate vaccine strain CHv-ΔgC/gE. The double gene deletion strain (CHv-ΔgC/gE) constructed in this study has greatly weakened virulence, no pathogenicity to ducks, and stable genetic characteristics in vitro and in vivo. Ducks immunized with CHv-ΔgC/gE can produce neutralizing antibodies and ELISA antibody levels comparable to those of commercial duck plague attenuated vaccine immunization, and can resist 100 LD₅₀ CHv challenge of ducks, with good immune protection effect. It has the potential to be further developed into duck plague gC/gE double gene deletion, marked attenuated vaccine.

Evaluation of the Safety and Immunogenicity of Duck-Plague Virus gE Mutants

Duck plague (DP) is an acute infectious disease in the duck industry. The duck plague virus (DPV) is the pathogen, a subfamily of alphaherpesvirinae. gE is a type I membrane protein that contains three parts: an extracellular domain, a transmembrane domain, and a cytoplasmic domain. gE is the major virulence determinant of α-herpesvirus. However, the functions of the gE extracellular and cytoplasmic domains have not been reported in DPV. In this study, a gE extracellular domain deletion mutant and a gE cytoplasmic domain deletion mutant were constructed from DPV. Virus replication kinetics showed that the growth titers of both the gE ectodomain-deleted mutant virus and the gE cytoplasmic domain-deleted virus in DEFs were lower than that of the parental virus CHv-50. DPV CHv-gEΔET and DPV CHv-gEΔCT were continuously passed to the 20th passage in DEFs and the 10th in ducklings. The mutant virus DNA after passage was extracted for identification. The results showed that the gE ectodomain and gE cytoplasmic domain deletion mutant viruses have good genetic stability. The ducklings in each group (n=10) were inoculated with the same titers of DPV CHv-gEΔET, DPV CHv-gEΔCT, DPV CHv-ΔgE, and parental CHv-50, respectively. Clinical symptoms and serum antibody levels were detected after inoculation. The results showed that the virulence of DPV CHv-gEΔCT to ducklings was reduced compared with parental CHv-50, while the virulence of DPV CHv-gEΔET to ducklings was significantly reduced. 10⁵ TCID₅₀ DPV CHv-gEΔET or DPV CHv-ΔgE can induce ducklings to produce DPV-specific antibodies, protect the ducklings from virulent CHv challenge. Therefore, DPV CHv-gEΔET may serve as a promising vaccine candidate to prevent and control duck plague.

CRISPR/Cas9 Editing of Duck Enteritis Virus Genome for the Construction of a Recombinant Vaccine Vector Expressing ompH Gene of Pasteurella multocida in Two Novel Insertion Sites

Duck enteritis virus (DEV) and Pasteurella multocida, the causative agent of duck plague and fowl cholera, are acute contagious diseases and leading causes of morbidity and mortality in duck. The NHEJ-CRISPR/Cas9-mediated gene editing strategy, accompanied with the Cre–Lox system, have been employed in the present study to show that two new sites at UL55-LORF11 and UL44-44.5 loci in the genome of the attenuated Jansen strain of DEV can be used for the stable expression of the outer membrane protein H (ompH) gene of P. multocida that could be used as a bivalent vaccine candidate with the potential of protecting ducks simultaneously against major viral and bacterial pathogens. The two recombinant viruses, DEV-OmpH-V5-UL55-LORF11 and DEV-OmpH-V5-UL44-44.5, with the insertion of ompH-V5 gene at the UL55-LORF11 and UL44-44.5 loci respectively, showed similar growth kinetics and plaque size, compared to the wildtype virus, confirming that the insertion of the foreign gene into these did not have any detrimental effects on DEV. This is the first time the CRISPR/Cas9 system has been applied to insert a highly immunogenic gene from bacteria into the DEV genome rapidly and efficiently. This approach offers an efficient way to introduce other antigens into the DEV genome for multivalent vector.

The LORF5 Gene Is Non-essential for Replication but Important for Duck Plague Virus Cell-to-Cell Spread Efficiently in Host Cells

Duck plague virus (DPV) can cause high morbidity and mortality in many waterfowl species within the order Anseriformes. The DPV genome contains 78 open reading frames (ORFs), among which the LORF2, LORF3, LORF4, LORF5, and SORF3 genes are unique genes of avian herpesvirus. In this study, to investigate the role of this unique LORF5 gene in DPV proliferation, we generated a recombinant virus that lacks the LORF5 gene by a two-step red recombination system, which cloned the DPV Chinese virulent strain (DPV CHv) genome into a bacterial artificial chromosome (DPV CHv-BAC); the proliferation law of LORF5-deleted mutant virus on DEF cells and the effect of LORF5 gene on the life cycle stages of DPV compared with the parent strain were tested. Our data revealed that the LORF5 gene contributes to the cell-to-cell transmission of DPV but is not relevant to virus invasion, replication, assembly, and release formation. Taken together, this study sheds light on the role of the avian herpesvirus-specific gene LORF5 in the DPV proliferation life cycle. These findings lay the foundation for in-depth functional studies of the LORF5 gene in DPV or other avian herpesviruses.

The intracellular domain of duck plague virus glycoprotein E affects UL11 protein incorporation into viral particles

Studies have shown that proteins in the tegument (located between the viral capsid and envelope layer) play critical roles in the assembly and budding of herpesviruses. The UL11 protein of herpesviruses is important in the process of virus particle cell entry, release, assembly and secondary envelopment. Herpesvirus glycoprotein E (gE) is involved in syncytia formation, transmission between cells and nerve invasion. In herpes simplex virus, UL11 has been shown to interact with gE. However, little is known about the relationship of duck plague virus (DPV) pUL11 and gE. In this study, we constructed DPV cytoplasmic domain (CT)-gE, and extracellular domain (ET)-gE deletion mutants, pCMV-gE, CT-gE, and ET-gE and UL11 recombinant plasmids. We found that pUL11 can interact and colocalize with gE, CT-gE and ET-gE. Together, these results highlight an important role for UL11 in the function of gE, and may also have important implications for the role of pUL11 and gE.

SC75741 antagonizes vesicular stomatitis virus, duck Tembusu virus, and duck plague virus infection in duck cells through promoting innate immune responses

Duck Tembusu virus (DTMUV) and duck plague virus (DPV) are typical DNA and RNA viruses of waterfowl, causing drastic economic losses to the duck farm industry in terms of high mortality and decreased egg production. These 2 viruses reappear from time to time because the available vaccines fail to provide complete immunity and no clinical antiviral drugs are available for them. In the present study, we evaluated the antiviral activity of SC75741 for DTMUV, DPV, and the model virus, vesicular stomatitis virus infection in duck cells. SC75741, a nuclear factor-kappa B (NF-κB)-specific inhibitor in mammal cells, revealed the highest antiviral activity among the inhibitors specific to c-Jun NH₂-terminal kinase, extracellular signal-regulated kinase, p38 mitogen-activated protein kinase (p38), and NF-κB signaling. The antiviral activity of SC75741 was dose-dependent and showed effects in different duck cell types. Time-addition and duration assay demonstrated that SC75741 inhibited virus infection in the middle of and after virus infection at least for 72 h in duck embro fibroblast cells. The DPV viral adsorption and genomic copy number were reduced, indicating that SC75741 blocks the phase of the virus life cycle at viral entry and genomic replication. In addition, SC75741 enhanced the expression of interferon only when stimulator of interferon genes (STING) was overexpressed or pre-activated by the virus infection, suggesting that SC75741 acts as a STING agonist. In conclusion, SC75741 is a candidate antiviral agent for DTMUV and DPV.

DPV UL41 gene encoding protein induces host shutoff activity and affects viral replication

The virion host shutoff (VHS) protein, encoded by the UL41 gene of herpes simplex virus (HSV), specifically degrades mRNA and induces host shutoff. VHS and its homologs are highly conserved in the Alphaherpesvirinae subfamily. However, the role of the duck plague virus (DPV) UL41 gene is unclear. In this study, we found that the DPV UL41 gene-encoded protein (pUL41) degrades RNA polymerase (pol) II-transcribed translatable RNA and induces protein synthesis shutoff. DPV pUL41 was dispensable for viral replication, but the UL41-deleted mutant virus exhibited a significant viral growth defect and plaque size reduction in Duck embryo fibroblast (DEF) cells. Furthermore, DPV pUL41 regulated viral mRNA accumulation to affect viral DNA replication, release and cell-to-cell spread.

Duck Enteritis Virus VP16 Antagonizes IFN-β-Mediated Antiviral Innate Immunity

Duck enteritis virus (DEV) can successfully evade the host innate immune responses and establish a lifelong latent infection in the infected host. However, the study about how DEV escapes host innate immunity is still deficient up to now. In this study, for the first time, we identified a viral protein VP16 by which DEV can obviously downregulate the production of IFN-β in duck embryo fibroblast (DEF). Our results showed that ectopic expression of VP16 decreased duck IFN-β (duIFN-β) promoter activation and significantly inhibited the mRNA transcription of IFN-β. Further study showed that VP16 can also obviously inhibit the mRNA transcription of interferon-stimulated genes (ISGs), such as myxovirus resistance protein (Mx) and interferon-induced oligoadenylate synthetase-like (OASL). Furthermore, we found that this anti-interferon activity of VP16 depended on its N-terminus (aa1-200). Coexpression analysis revealed that VP16 selectively blocked duIFN-β promoter activity at the duIRF7 level rather than duIRF1. Based on the results of coimmunoprecipitation analysis (co-IP) and indirect immunofluorescence assay (IFA), VP16 was able to bind to duck IRF7 (duIRF7) directly, but did not interact with duck IRF1 (duIRF1) in vitro.

The Pivotal Roles of US3 Protein in Cell-to-Cell Spread and Virion Nuclear Egress of Duck Plague Virus

The duck plague virus (DPV) US3 protein, a homolog of the herpes simplex virus-1 (HSV-1) US3 protein that is reported to be critical for viral replication, has been minimally studied. Therefore, to investigate the function of the DPV US3 protein, we used scarless Red recombination technology based on an infectious bacterial artificial chromosome (BAC) containing the DPV Chinese virulent strain (CHv) genome and successfully constructed and rescued a US3-deleted mutant and the corresponding revertant virus (BAC-CHv-ΔUS3 and BAC-CHv-ΔUS3R, respectively). For viral growth characteristics, compared to the parental and revertant viruses, the US3-deleted mutant showed an approximately 100-fold reduction in viral titers but no significant reduction in genome copies, indicating that the US3-deleted mutant exhibited decreased viral replication but not decreased viral DNA generation. In addition, the US3-deleted mutant formed viral plaques that were 33% smaller on average than those formed by the parental and revertant viruses, demonstrating that US3 protein affected the viral cell-to-cell spread of DPV. Finally, the results of electron microscopy showed that the deletion of US3 resulted in a large number of virions accumulating in the nucleus and perinuclear space, thus blocking virion nuclear egress. In this study, we found that the DPV US3 protein played pivotal roles in viral replication by promoting viral cell-to-cell spread and virion nuclear egress, which may provide some references for research on the function of the DPV US3 protein.

Duck plague virus gE serves essential functions during the virion final envelopment through influence capsids budding into the cytoplasmic vesicles

Duck plague virus (DPV), a member of the alphaherpesviruses subfamily, causes massive ducks death and results in a devastating hit to duck industries in China. It is of great significance for us to analyze the functions of DPV genes for controlling the outbreak of duck plague. Thus, glycoproteins E (gE) of DPV, which requires viral cell-to-cell spreading and the final envelopment in herpes simplex virus 1 (HSV-1) and pseudorabies virus (PRV), was chosen herein. The gE mutant virus BAC-CHv-ΔgE was constructed by using a markerless two-step Red recombination system implemented on the DPV genome cloned into a bacterial artificial chromosome (BAC). Viral plaques on duck embryo fibroblast (DEF) cells of BAC-CHv-ΔgE were on average approximately 60% smaller than those produced by BAC-CHv virus. Viral replication kinetics showed that BAC-CHv-ΔgE grew to lower titers than BAC-CHv virus did in DEF cells. Electron microscopy confirmed that deleting of DPV gE resulted in a large number of capsids accumulating around vesicles and very few of them could bud into vesicles. The drastic inhibition of virion formation in the absence of the DPV gE indicated that it played an important role in virion morphogenesis before the final envelopment of intracytoplasmic nucleocapsids.

Duplicate US1 Genes of Duck Enteritis Virus Encode a Non-essential Immediate Early Protein Localized to the Nucleus

The duplicate US1 genes of duck enteritis virus (DEV) encode a protein with a conserved Herpes_IE68 domain, which was found to be closely related to the herpes virus immediate early regulatory protein family and is highly conserved among counterparts encoded by Herpes_IE68 genes. Previous studies found the homologous proteins HSV-1 ICP22 and VZV ORF63/ORF70 to be critical for virus transcription and replication. However, little is known about the DEV ICP22 protein. In this paper, we describe the characteristics of this protein based on pharmacological experiments, real-time quantitative Polymerase Chain Reaction, Western blot, and immunofluorescence assays. We also investigate the role of the protein in DEV replication via mutation of US1. As a result, we found that the DEV ICP22 protein is a non-essential immediate early protein predominantly located in the nucleus of infected DEF cells and that DEV replication is impaired by US1 deletion. We also found that ICP22 contains a classical nuclear localization signal (NLS) at 305-312AA, and ICP22 cannot enter the nucleus by itself after mutating residue 309.

Alpha-Herpesvirus Thymidine Kinase Genes Mediate Viral Virulence and Are Potential Therapeutic Targets

Alpha-herpesvirus thymidine kinase (TK) genes are virulence-related genes and are nonessential for viral replication; they are often preferred target genes for the construction of gene-deleted attenuated vaccines and genetically engineered vectors for inserting and expressing foreign genes. The enzymes encoded by TK genes are key kinases in the nucleoside salvage pathway and have significant substrate diversity, especially the herpes simplex virus 1 (HSV-1) TK enzyme, which phosphorylates four nucleosides and various nucleoside analogues. Hence, the HSV-1 TK gene is exploited for the treatment of viral infections, as a suicide gene in antitumor therapy, and even for the regulation of stem cell transplantation and treatment of parasitic infection. This review introduces the effects of α-herpesvirus TK genes on viral virulence and infection in the host and classifies and summarizes the current main application domains and potential uses of these genes. In particular, mechanisms of action, clinical limitations, and antiviral and antitumor therapy development strategies are discussed.

US10 Protein Is Crucial but not Indispensable for Duck Enteritis Virus Infection in Vitro

To investigate the function of the duck enteritis virus (DEV) tegument protein US10, we generated US10 deletion and revertant mutants (ΔUS10 and US10FRT) via two-step RED recombination based on an infectious BAC clone of DEV CHv-BAC-G (BAC-G). In multistep growth kinetic analyses, ΔUS10 showed an approximately 100-fold reduction in viral titer, while the genome copies decreased only 4-fold compared to those of BAC-G. In one-step growth kinetic analyses, there were no significant differences in genome copies among BAC-G, ΔUS10 and US10FRT, but ΔUS10 still showed a 5- to 20-fold reduction in viral titer, and the replication defect of ΔUS10 was partially reversed by infection of US10-expressing cells. The transcription levels of Mx, OASL, IL-4, IL-6 and IL-10 in ΔUS10-infected duck embryo fibroblasts (DEFs) were significantly upregulated, while TLR3 was downregulated compared with those in BAC-G-infected DEFs. Taken together, these data indicated that US10 is vital for DEV replication and is associated with transcription of some immunity genes.

Duck plague virus Glycoprotein J is functional but slightly impaired in viral replication and cell-to-cell spread

To analyse the function of the duck plague virus (DPV) glycoprotein J homologue (gJ), two different mutated viruses, a gJ deleted mutant ΔgJ and a gJR rescue mutant gJR with US5 restored were generated. All recombinant viruses were constructed by using two-step of RED recombination system implemented on the duck plague virus Chinese virulent strain (DPV CHv) genome cloned into a bacterial artificial chromosome. DPV-mutants were characterized on non-complementing DEF cells compared with parental virus. Viral replication kinetics of intracellular and extracellular viruses revealed that the ΔgJ virus produce a 10-fold reduction of viral titers than the gJR and parental virus, which especially the production of extracellular infectivity was affected. In addition, the ΔgJ virus produced viral plaques on DEF cells that was on average approximately 11% smaller than those produced by the gJR and parental viruses. Electron microscopy confirmed that although DPV CHv without gJ could efficiently carry out viral replication, virion assembly and envelopment within infected cells, the ΔgJ virus produced and accumulated high levels of anuclear particles in the nuclear and cytoplasm. These results show that the gJ slightly impaired in viral replication, virion assembly and cell-to-cell spread, and is not essential in virion envelopment.