Expressing gK gene of duck enteritis virus guided by bioinformatics and its applied prospect in diagnosis

Alphaherpesvirus glycoprotein E: A review of its interactions with other proteins of the virus and its application in vaccinology

The viral envelope glycoprotein E (gE) is required for cell-to-cell transmission, anterograde and retrograde neurotransmission, and immune evasion of alphaherpesviruses. gE can also interact with other proteins of the virus and perform various functions in the virus life cycle. In addition, the gE gene is often the target gene for the construction of gene-deleted attenuated marker vaccines. In recent years, new progress has been made in the research and vaccine application of gE with other proteins of the virus. This article reviews the structure of gE, the relationship between gE and other proteins of the virus, and the application of gE in vaccinology, which provides useful information for further research on gE.

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.

Cloning and functional analysis of squalene synthase gene from Dryopteris fragrans (L.) Schott

Dryopteris fragrans (L.) Schott is a traditional herbal medicine containing medicinal sterols and triterpenoids. Squalene synthase (SQS) is the first crucial enzyme in the biosynthesis pathway of sterols and triterpenoids. The full-length cDNA named DfSQS1 was isolated by RACE. It was predicted that DfSQS1 contained an open reading frame (ORF) of 1239 bp coding 412 amino acid residues with molecular weight of 46.6 kDa. It had 18 potential phosphorylation sites, 1 potential N-glycosylation site and 2 transmembrane domains. In neighbor-joining (NJ) phylogenetic tree, DfSQS1 was away from branch of gymnosperms and angiosperms. One hydrophobic domain at the C-terminal of DfSQS1 was deleted to express soluble recombinant enzyme. The truncated DfSQS1 (tDfSQS1) was expressed in Escherichia coli BL21 (DE3). Then, tDfSQS1 was obtained and incubated with farnesyl diphosphate (FPP) to identify its enzymatic activity. The result demontrated that squalene, the product of enzyme catalyzed reaction, was detected by HPLC. Quantitative real-time PCR (qRT-PCR) analysis revealed that the transcription level of DfSQS1 in D. fragrans was the highest in roots, followed by leaves and rhizomes. This work is the first report on cloning, characteration and expression of SQS from D. fragrans. It will be helpful to understand the regulatory role of SQS on the biosynthesis of triterpenoids in the fern.

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.

Programmed cell death: the battlefield between the host and alpha-herpesviruses and a potential avenue for cancer treatment

Programed cell death is an antiviral mechanism by which the host limits viral replication and protects uninfected cells. Many viruses encode proteins resistant to programed cell death to escape the host immune defenses, which indicates that programed cell death is more favorable for the host immune defense. Alpha-herpesviruses are pathogens that widely affect the health of humans and animals in different communities worldwide. Alpha-herpesviruses can induce apoptosis, autophagy and necroptosis through different molecular mechanisms. This review concisely illustrates the different pathways of apoptosis, autophagy, and necroptosis induced by alpha-herpesviruses. These pathways influence viral infection and replication and are a potential avenue for cancer treatment. This review will increase our understanding of the role of programed cell death in the host immune defense and provides new possibilities for cancer treatment.

Duck virus enteritis (duck plague) - a comprehensive update

Duck virus enteritis (DVE), also called duck plague, is one of the major contagious and fatal diseases of ducks, geese and swan. It is caused by duck enteritis virus (DEV)/Anatid herpesvirus-1 of the genus Mardivirus, family Herpesviridae, and subfamily Alpha-herpesvirinae. Of note, DVE has worldwide distribution, wherein migratory waterfowl plays a crucial role in its transmission within and between continents. Furthermore, horizontal and/ or vertical transmission plays a significant role in disease spread through oral-fecal discharges. Either of sexes from varying age groups of ducks is vulnerable to DVE. The disease is characterized by sudden death, vascular damage and subsequent internal hemorrhage, lesions in lymphoid organs, digestive mucosal eruptions, severe diarrhea and degenerative lesions in parenchymatous organs. Huge economic losses are connected with acute nature of the disease, increased morbidity and mortality (5%-100%), condemnations of carcasses, decreased egg production and hatchability. Although clinical manifestations and histopathology can provide preliminary diagnosis, the confirmatory diagnosis involves virus isolation and detection using serological and molecular tests. For prophylaxis, both live-attenuated and killed vaccines are being used in broiler and breeder ducks above 2 weeks of age. Since DEV is capable of becoming latent as well as shed intermittently, recombinant subunit and DNA vaccines either alone or in combination (polyvalent) are being targeted for its benign prevention. This review describes DEV, epidemiology, transmission, the disease (DVE), pathogenesis, and advances in diagnosis, vaccination and antiviral agents/therapies along with appropriate prevention and control strategies.

Expression of core antigen of HCV genotype 3a and its evaluation as screening agent for HCV infection in Pakistan

Background

Pakistan is facing a threat from hepatitis C infection which is increasing at an alarming rate throughout the country. More specific and sensitive screening assays are needed to timely and correctly diagnose this infection.

Methods

After RNA extraction from specimen (HCV-3a), cDNA was synthesized that was used to amplify full length core gene of HCV 3a. After verification through PCR, DNA sequencing and BLAST, a properly oriented positive recombinant plasmid for core gene was digested with proper restriction enzymes to release the target gene which was then inserted downstream of GST encoding DNA in the same open reading frame at proper restriction sites in multiple cloning site of pGEX4t2 expression vector. Recombinant expression vector for each gene was transformed in E. coli BL21 (DE3) and induced with IPTG for recombinant fusion protein production that was then purified through affinity chromatography. Western blot and Enzyme Linked Immunosorbant Assay (ELISA) were used to detect immuno-reactivity of the recombinant protein.

Results

The HCV core antigen produced in prokaryotic expression system was reactive and used to develop a screening assay. After validating the positivity (100%) and negativity (100%) of in-house anti-HCV screening assay through a standardized panel of 200 HCV positive and 200 HCV negative sera, a group of 120 serum specimens of suspected HCV infection were subjected to comparative analysis of our method with commercially available assay. The comparison confirmed that our method is more specific than the commercially available assays for HCV strains circulating in this specific geographical region of the world and could thus be used for HCV screening in Pakistan.

Conclusion

In this study, we devised a screening assay after successful PCR amplification, isolation, sequencing, expression and purification of core antigen of HCV genotype 3a. Our developed screening assay is more sensitive, specific and reproducible than the commercially available screening assays in Pakistan.

Complete genome sequence of virulent duck enteritis virus (DEV) strain 2085 and comparison with genome sequences of virulent and attenuated DEV strains

We here report the complete genome sequence of the duck enteritis virus (DEV) wild-type strain 2085, an avian herpesvirus (GenBank ID: JF999965). The nucleotide sequence was derived from the 2085 genome cloned as an infectious bacterial artificial chromosome (BAC) clone. The DEV 2085 genome is 160,649-bp in length and encodes 78 predicted open reading frames (ORFs), a number identical to that identified for the attenuated DEV VAC strain (GenBank ID: EU082088.2). Comparison of the genome sequences DEV 2085 and VAC with partial sequences of the virulent CHv strain and the attenuated strain Clone-03 was carried out to identify nucleotide or amino acid polymorphisms that potentially contribute to DEV virulence. No amino acid changes were identified in 24 of the 78 ORFs, a result indicating high conservation in DEV independently of strain origin or virulence. In addition, 39 ORFs contain non-synonymous nucleotide substitutions, while 15 ORFs had nucleotide insertions or deletions, frame-shift mutations and/or non-synonymous nucleotide substitutions with an effect on ORF initiation or termination. In 7 of the 15 ORFs with high and 27 of the 39 ORFs with low variability, polymorphisms were exclusively found in DEV 2085, a finding that likely is a result of a different origin of 2085 (Europe) or VAC, Clone-03 and CHv (Eastern Asia). Five ORFs (UL2, UL12, US10, UL47 and UL41) with polymorphisms were identical between the virulent DEV 2085 and CHv but different from VAC or Clone-03. They, individually or in combination, may therefore represent DEV virulence factors. Our comparative analysis of four DEV sequences provides a comprehensive overview of DEV genome structure and identifies ORFs that are changed during serial virus passage.

Characterization of the duck enteritis virus UL55 protein

Background

Characteration of the newly identified duck enteritis virus UL55 gene product has not been reported yet. Knowledge of the protein UL55 can provide useful insights about its function.

Results

The newly identified duck enteritis virus UL55 gene was about 561 bp, it was amplified and digested for construction of a recombinant plasmid pET32a(+)/UL55 for expression in Escherichia coli. SDS-PAGE analysis revealed the recombinant protein UL55(pUL55) was overexpressed in Escherichia coli BL21 host cells after induction by 0.2 mM IPTG at 37°C for 4 h and aggregated as inclusion bodies. The denatured protein about 40 KDa named pUL55 was purified by washing five times, and used to immune rabbits for preparation of polyclonal antibody. The prepared polyclonal antibody against pUL55 was detected and determined by Agar immundiffusion and Neutralization test. The results of Wstern blotting assay and intracellular analysis revealed that pUL55 was expressed most abundantly during the late phase of replication and mainly distributed in cytoplasm in duck enteritis virus infected cells.

Conclusions

In this study, the duck enteritis virus UL55 protein was successfully expressed in prokaryotic expression system. Besides, we have prepared the polyclonal antibody against recombinant prtein UL55, and characterized some properties of the duck enteritis virus UL55 protein for the first time. The research will be useful for further functional analysis of this gene.

Expression and characterization of duck enteritis virus gI gene

BACKGROUND

At present, alphaherpesviruses gI gene and its encoding protein have been extensively studied. It is likely that gI protein and its homolog play similar roles in virions direct cell-to-cell spread of alphaherpesviruses. But, little is known about the characteristics of DEV gI gene. In this study, we expressed and presented the basic properties of the DEV gI protein.

RESULTS

The special 1221-bp fragment containing complete open reading frame(ORF) of duck enteritis virus(DEV) gI gene was extracted from plasmid pMD18-T-gI, and then cloned into prokaryotic expression vector pET-32a(+), resulting in pET-32a(+)-gI. After being confirmed by PCR, restriction endonuclease digestion and sequencing, pET-32a(+)-gI was transformed into E.coli BL21(DE3) competent cells for overexpression. DEV gI gene was successfully expressed by the addition of isopropyl-β-D-thiogalactopyranoside(IPTG). SDS-PAGE showed that the recombinant protein His6-tagged gI molecular weight was about 61 kDa. Subsequently, the expressed product was applied to generate specific antibody against gI protein. The specificity of the rabbit immuneserum was confirmed by its ability to react with the recombinant protein His6-tagged gI. In addition, real time-PCR was used to determine the the levels of the mRNA transcripts of gI gene, the results showed that the DEV gI gene was transcribed most abundantly during the late phase of infection. Furthermore, indirect immunofluorescence(IIF) was established to study the gI protein expression and localization in DEV-infected duck embryo fibroblasts (DEFs), the results confirmed that the protein was expressed and located in the cytoplasm of the infected cells, intensively.

CONCLUSIONS

The recombinant prokaryotic expression vector of DEV gI gene was constructed successfully. The gI protein was successfully expressed by E.coli BL21(DE3) and maintained its antigenicity very well. The basic information of the transcription and intracellular localization of gI gene were presented, that would be helpful to assess the possible role of DEV gI gene. The research will provide useful clues for further functional analysis of DEV gI gene.

Characterization of duck enteritis virus UL53 gene and glycoprotein K

Background

Most of the previous research work had focused on the epidemiology and prevention of duck enteritis virus (DEV). Whilst with the development of protocols in molecular biology, nowadays more and more information about the genes of DEV was reported. But little information about DEV UL53 gene and glycoprotein K(gK) was known except our reported data.

Results

In our paper, the fluorescent quantitative real-time PCR(FQ-RT-PCR) assay and nucleic acid inhibition test were used to study the transcription characteristic of the DEV UL53 gene. Except detecting the mRNA of DEV UL53 gene, the product gK encoded by UL53 gene was detected through the expression kinetics of UL53 gene by the purified rabbit anti-UL53 protein polyclonal antibodies. Western-blotting and indirect immunofluorescence assays were used to detect gK. From the results of these experiments, the UL53 gene and gK were respectively identified as a late gene and a really late protein. On the other hand, the indirect immunofluorescence assay provided another information that the intracellular localization of DEV gK was mainly distributed in cytoplasm.

Conclusions

By way of conclusions, we conceded that DEV UL53 gene is a really late gene, which is coincident with properties of UL53 homologs from other herpesvirus, such as ILTV(Infectious Laryngotracheitis virus) and HSV-1(Herpes simplex virus type 1). The properties of intracellular localization about gK protein provided a foundation for further functional analysis and further studies will be focused on constructing of the UL53 gene DEV mutant.

Expression and characterization of recombinant VP19c protein and N-terminal from duck enteritis virus

Background

Previous studies have indicated that the VP19c protein and its homology play similar roles in capsid assembly of all Alphaherpesvirus subfamily. However, there is no report on the VP19c protein of duck enteritis virus (DEV). In this study, we expressed the DEV VP19c protein and presented its antigenic properties. Moreover, we developed polyclonal antibody against the VP19c protein and characterized it.

Methods

A recombinant VP19c (rVP19c) and N-terminal were expressed in Escherichia coli (E.coli) and purified by Ni2+-affinity chromatography. The antigenic properties of the recombinant protein were determined by Western blot and indirect enzyme-linked immunosorbent assay (ELISA). Furthermore, the polyclonal antibodies against the purified recombinant proteins were produced and the titer of polyclonal antibody was determined by ELISA analysis. Finally, the antibody was used to recognize the VP19c in the cells infected with DEV in the immunofluorescence assay.

Results

The N-terminally His-tagged rVP19c and rVP19c(N) were produced as inclusion bodies in E. coli strain BL21 (DE3) with molecular weight of about 66 and 46 kDa. Then the proteins were purified to reach the level of homogeneity. Western blot and ELISA analysis that the rVP19c seems to be structurally and antigenically very similar to native VP19c and the N-terminus of VP19c may contain most antigenic linear-epitopes. Furthermore, ELISA analysis demonstrated that the titer of polyclonal antibody was approximately 1:12800, and in the immunofluorescence assay, the antibody was able to recognize the VP19c in the cells infected with DEV.

Conclusions

To our knowledge, this was the first report on basic properties of DEV VP19c protein. In the present study, we obtained a high-level expression of the recombinant VP19c protein as well as high titers of rabbit polyclonal antibody against to VP19c protein. The anti-rVP19c serum was able to detect the VP19c protein in DEV infected cells and the VP19c protein targeted to the nucleus as distinct punctate speckles. This specific polyclonal antibody provides a good tool for further studying structural and functional characterization of DEV VP19c.

Production, purification and characterization of polyclonal antibody against the truncated gK of the duck enteritis virus

Duck virus enteritis (DVE) is an acute, contagious herpesvirus infection of ducks, geese, and swans, which has produced significant economic losses in domestic and wild waterfowl. With the purpose of decreasing economic losses in the commercial duck industry, studying the unknown glycoprotein K (gK) of DEV may be a new method for preferably preventing and curing this disease. So this is the first time to product and purify the rabbit anti-tgK polyclonal antibody. Through the western blot and ELISA assay, the truncated glycoprotein K (tgK) has good antigenicity, also the antibody possesses high specificity and affinity. Meanwhile the rabbit anti-tgK polyclonal antibody has the potential to produce subunit vaccines and the functions of neutralizing DEV and anti-DEV infection because of its neutralization titer. Indirect immunofluorescent microscopy using the purified rabbit anti-tgK polyclonal antibody as diagnostic antibody was susceptive to detect a small quantity of antigen in tissues or cells. This approach also provides effective experimental technology for epidemiological investigation and retrospective diagnose of the preservative paraffin blocks.