Establishment of real-time quantitative reverse transcription polymerase chain reaction assay for transcriptional analysis of duck enteritis virus UL55 gene

Equine Arteritis Virus in Monocytic Cells Suppresses Differentiation and Function of Dendritic Cells

Equine viral arteritis is an infectious disease of equids caused by equine arteritis virus (EAV), an RNA virus of the family Arteriviridae. Dendritic cells (DC) are important modulators of the immune response with the ability to present antigen to naïve T cells and can be generated in vitro from monocytes (MoDC). DC are important targets for many viruses and this interaction is crucial for the establishment-or rather not-of an anti-viral immunity. Little is known of the effect EAV has on host immune cells, particularly DC. To study the interaction of eqDC with EAV in vitro, an optimized eqMoDC system was used, which was established in a previous study. MoDC were infected with strains of different genotypes and pathogenicity. Virus replication was determined through titration and qPCR. The effect of the virus on morphology, phenotype and function of cells was assessed using light microscopy, flow cytometry and in vitro assays. This study confirms that EAV replicates in monocytes and MoDC. The replication was most efficient in mature MoDC, but variable between strains. Only the virulent strain caused a significant down-regulation of certain proteins such as CD14 and CD163 on monocytes and of CD83 on mature MoDC. Functional studies conducted after infection showed that EAV inhibited the endocytic and phagocytic capacity of Mo and mature MoDC with minimal effect on immature MoDC. Infected MoDC showed a reduced ability to stimulate T cells. Ultimately, EAV replication resulted in an apoptosis-mediated cell death. Thus, EAV evades the host anti-viral immunity both by inhibition of antigen presentation early after infection and through killing infected DC during replication.

Identification of RT-qPCR reference genes suitable for gene function studies in the pitaya canker disease pathogen Neoscytalidium dimidiatum

Neoscytalidium dimidiatum is the main causal agent of pitaya canker. Most studies of virulence and pathogenicity genes have measured expression levels using real-time quantitative polymerase chain reaction (RT-qPCR). Suitable reference genes are essential for ensuring that estimates of gene expression levels by RT-qPCR are accurate. However, no reference genes can be robustly applied across all contexts and species. No studies to date have evaluated the most effective reference genes for normalizing gene expression levels estimated by RT-qPCR in N. dimidiatum. In this study, RT-qPCR data for individual candidate reference genes were analyzed using four different methods: the delta Ct method and the geNorm, NormFinder, and BestKeeper algorithms. We evaluated the utility of eight candidate reference genes (18S rRNA, Actin (1), Actin (2), Actin, GAPDH (1), GAPDH (2), UBQ, and Tubulin) for normalizing expression levels estimated by RT-qPCR in N. dimidiatum at different developmental stages, at different temperatures, and during interaction with pitaya. All candidate reference genes were suitable for gene expression analysis except for Actin (2). Tubulin and Actin (1) were the most stably expressed reference genes under different temperatures. Actin (1) and Actin were the most stably expressed reference genes in N. dimidiatum at different developmental stages. Tubulin and UBQ were the most stably expressed reference genes during interaction with pitaya. Actin and 18s rRNA were the most stably expressed across all experimental conditions. Subsequently, Tubulin and UBQ were further investigated in analyses of pectinase expression during the pitaya-N. dimidiatum interaction. Our results provide insights that will aid future RT-qPCR studies of gene expression in N. dimidiatum.

Duck plague virus UL41 protein inhibits RIG-I/MDA5-mediated duck IFN-β production via mRNA degradation activity

Retinoic acid-inducible gene I (RIG-I)-like receptors (RLRs) are cytosolic pattern recognition receptors that initiate innate antiviral immunity. Recent reports found that duck RLRs significantly restrict duck plague virus (DPV) infection. However, the molecular mechanism by which DPV evades immune responses is unknown. In this study, we first found that the DPV UL41 protein inhibited duck interferon-β (IFN-β) production mediated by RIG-I and melanoma differentiation-associated gene 5 (MDA5) by broadly downregulating the mRNA levels of important adaptor molecules, such as RIG-I, MDA5, mitochondrial antiviral signalling protein (MAVS), stimulator of interferon gene (STING), TANK-binding kinase 1 (TBK1), and interferon regulatory factor (IRF) 7. The conserved sites of the UL41 protein, E229, D231, and D232, were responsible for this activity. Furthermore, the DPV CHv-BAC-ΔUL41 mutant virus induced more duck IFN-β and IFN-stimulated genes (Mx, OASL) production in duck embryo fibroblasts (DEFs) than DPV CHv-BAC parent virus. Our findings provide insights into the molecular mechanism underlying DPV immune evasion.

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.

Molecular cloning of duck CD40 and its immune function research

Cosignal molecules are cell surface molecules that transduce signals to other cells to modulate immune response positively (costimulate) or negatively (cosuppress). Costimulatory signals are key factors in determining whether T/B cells are capable of responding to specific antigens and ultimately mediating an appropriate immune response. In this study, the cDNA sequence containing the complete coding frame of the costimulatory molecule duck CD40 gene was cloned and reported for the first time, and its mediated antiviral innate immune was verified in vitro. Results suggested duck CD40 molecule plays an important role in the innate immune responsiveness against some viruses. These data will be beneficial for the further understand of the avian immune system.

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.

Development of a simple and rapid immunochromatographic strip test for detecting duck plague virus antibodies based on gI protein

A colloidal gold strip (CGS) for detecting antibodies to duck plague virus (DPV) was developed. Colloidal gold-labeled DPV gI protein and goat anti-rabbit IgG were dispensed on a conjugate pad as tracers. The recombinant DPV gI protein and rabbit IgG were used as capture reagents at the test line and control line, respectively. The detection limit of this assay was 1:256. Additionally, the CGS did not react with antisera from other common duck diseases, only reacting with anti-DPV serum and yielding a specific and strong red signal. 123 serum samples were tested by CGS and enzyme-linked immunosorbent assay (ELISA), and the results showed good agreement. The CGS test results can be observed in 15 min with the naked eye, should be suitable for clinical testing and large-scale detection.

Determination of Suitable RT-qPCR Reference Genes for Studies of Gene Functions in Laodelphax striatellus (Fallén)

The reverse transcription quantitative polymerase chain reaction (RT-qPCR) has been widely used to determine gene functions in Laodelphax striatellus (Fallén) (small brown planthopper). Selection of suitable reference gene(s) for normalizations of RT-qPCR data is critical for reliable results. To date, reports on identification of suitable L. striatellus reference genes are still very limited. L. striatellus is a destructive rice pest and it can transmit multiple viruses, including Rice black-streaked dwarf virus (RBSDV), Rice stripe virus (RSV), and Maize rough dwarf virus (MRDV), to many important cereal crops worldwide. In this study, we examined the stablity of seven selected candidate reference genes in L. striatellus at different developmental stages, in different tissues, in RBSDV- or RSV-infected L. striatellus or in RBSDV-infected and Lssynaptojanin 1 (LsSYNJ1)-silenced L. striatellus. The RT-qPCR data representing individual candidate genes were analyzed using five different methods: the delta Ct method, geNorm, NormFinder, BestKeeper, and the RefFinder algorithm, respectively. The most stable reference gene for the specific condition was selected according to a comprehensive analysis using the RefFinder method. Ribosomal protein L5 (LsRPL5) and LsRPL8 are the most stably expressed genes in L. striatellus at different developmental stages. Alpha-1-tubulin (Lsα-TUB) is the most stably expressed reference gene in different tissues of RBSDV viruliferous (RBSDV-V) or non-viruliferous (RBSDV-NV) L. striatellus. LsRPL8 is the most stably expressed reference gene in RBSDV-V or RSV viruliferous (RSV-V) L. striatellus, while beta-tubulin (Lsβ-TUB) is the most stably expressed reference gene in RBSDV-V and LsSYNJ1-silenced L. striatellus. The selected reference genes were further investigated during analyses of RBSDV P5-1 and P10 gene expression in different tissues from RBSDV-V or RBSDV-NV L. striatellus. The stably expressed reference genes identified in this study will benefit future gene function studies using L. striatellus.

Molecular characterization and antiapoptotic function analysis of the duck plague virus Us5 gene

Thus far, there have been no reports on the molecular characterization and antiapoptotic function of the DPV Us5 gene. To perform molecular characterization of DPV Us5, RT-PCR and pharmacological inhibition tests were used to ascertain the kinetic class of the Us5 gene. Western blotting and an indirect immunofluorescence assay (IFA) were used to analyze the expression level and subcellular localization of Us5 in infected cells at different time points. Us5 in purified DPV virions was identified by mass spectrometry. The results of RT-PCR, Western blotting, and pharmacological inhibition tests revealed that Us5 is transcribed mainly in the late stage of viral replication. The IFA results revealed that Us5 was localized throughout DPV-infected cells but was localized only to the cytoplasm of transfected cells. Mass spectrometry and Western blot analysis showed that Us5 was a virion component. Next, to study the antiapoptotic function of DPV Us5, we found that DPV CHv without gJ could induce more apoptosis cells than DPV-CHv BAC and rescue virus. we constructed a model of apoptosis in duck embryo fibroblasts (DEFs) induced by hydrogen peroxide (H₂O₂). Transfected cells expressing the Us5 gene were protected from apoptosis induced by H₂O₂, as measured by a TUNEL assay, a caspase activation assay and Flow Cytometry assay. The TUNEL assay and Flow Cytometry assay results showed that the recombinant plasmid pCAGGS-Us5 could inhibit apoptosis induced by H₂O₂ in DEF cells. However, caspase-3/7 and caspase-9 protein activity upregulated by H₂O₂ was significantly reduced in cells expressing the recombinant plasmid pCAGGS-Us5. Overall, these results show that the DPV Us5 gene is a late gene and that the Us5 protein is a component of the virion, is localized in the cytoplasm, and can inhibit apoptosis induced by H₂O₂ in DEF cells.

Duck plague outbreak in a Chara-Chemballi duck farm

BACKGROUND

Duck rearing is one of the important livelihoods of rural people. Duck plague is one of the diseases causing heavy mortality resulting in economic losses.

CASE DESCRIPTION

An outbreak of duck plague in a farm in Kadavakathi Village near Tenkasi, Tirunelveli Dt., is reported.

FINDINGS/TREATMENT AND OUTCOME

Two thousands out of 4500 Chara-Chemballi breed of ducks which were recently purchased from Chenganacherry in Kerala died, with a mortality rate of 44.4%. Clinical signs of inappetence, partial closure of eyelid, conjunctivitis, corneal opacity, oculo-nasal discharge, soiled vent with green white watery diarrhoea, ataxia, incoordination and sudden death were observed. Necropsy examination revealed diphtheritic membrane in the oesophagus, congestion, petechial haemorrhages and multifocal gray white areas on the surface of the liver, epicardial haemorrhages, congested trachea, lung, kidneys, splenomegaly with mottled appearance and enteritis. Microscopical examination revealed presence of eosinophilic intranuclear and intracytoplasmic inclusions in the epithelial cells of the intestine and hepatocytes, degeneration and necrosis of enterocytes, dilated crypt epithelial cells with presence of eosinophilic intranuclear and intracytoplasmic inclusions, congestion and lymphoid cell depletion in the spleen, vasculitis, congestion, and haemorrhages in the trachea and lungs, proventriculitis, and congested kidneys. Polymerase chain reaction (PCR) also confirmed the duck plague viral infection by the amplification of polymerase gene fragment (446 bp).

CONCLUSION

Based on the above findings, the Chara-Chemballi duck disease outbreak was diagnosed as duck viral enteritis infection.

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.

Molecular characterization of duck enteritis virus UL41 protein

BACKGROUND

Duck enteritis virus (DEV) belongs to the subfamily Alphaherpesvirinae, and information on the DEV UL41 gene is limited.

METHODS

The DEV UL41 gene was cloned into the pET32a(+) vector and expressed in a prokaryotic expression system. Antiserum was raised against a bacterially expressed UL41-His fusion protein for further experiments. Transcription was quantified and UL41 protein expression levels were determined in DEV-infected cells at different time points by RT-qPCR and western blotting, respectively. DEV virions were purified by sucrose gradient centrifugation and analyzed by mass spectrometry to identify protein content. We confirmed the DEV UL41 gene kinetic class using a pharmacological test. IFA was used to analyze the intracellular localization of pUL41.

RESULTS

The recombinant expression plasmid, pET-32a(+)-UL41, which highly expresses a 76.0 kDa fusion protein, was constructed and expressed in E. coli BL21 (DE3) after induction with 0.2 mM IPTG at 30 °C for 10 h, generating a specific mouse anti-UL41 protein polyclonal antibody. RT-qPCR and western blot analyses revealed that the UL41 transcript number peaked at 36 hpi, and peak protein expression occurred at 48 hpi. The pharmacological test showed that UL41 was a γ2 gene. Mass spectrometry analysis showed that pUL41 was a virion component. IFA results revealed that pUL41 was localized throughout DEV-infected cells but only localized to the cytoplasm of transfected cells. DEV pUL47 translocated pUL41 to the nuclei of DEF cells; this translocation was dependent on predicted pUL47 NLS signals (40-50 aa and 768-777 aa).

CONCLUSIONS

DEV UL41 is a γ2 gene that encodes a virion structural protein, pUL41 localizes throughout DEV-infected cells but only localizes to the cytoplasm of transfected cells. pUL41 cannot autonomously localize to the nucleus, as this nuclear localization is dependent on predicted DEV pUL47 NLS signals (40-50 aa and 768-777 aa).

Molecular characterization of the duck enteritis virus US10 protein

BACKGROUND

There is little information regarding the duck enteritis virus (DEV) US10 gene and its molecular characterization.

METHODS

Duck enteritis virus US10 was amplified and cloned into the recombinant vector pET32a(+). The recombinant US10 protein was expressed in Escherichia coli BL21 cells and used to immunize rabbits for the preparation of polyclonal antibodies. The harvested rabbit antiserum against DEV US10 was detected and analyzed by agar immunodiffusion. Using this antibody, western blotting and indirect immunofluorescence analysis were used to analyze the expression level and subcellular localization of US10 in infected cells at different time points. Quantitative reverse-transcription PCR (qRT-PCR) and pharmacological inhibition tests were used to ascertain the kinetic class of the US10 gene. A mass spectrometry-based strategy was used to identify US10 in purified DEV virions and quantify its abundance.

RESULTS

The recombinant pET32a(+)/US10 protein was expressed as inclusion bodies, purified by gradient urea washing, and used to prepare specific antibodies. The results of qRT-PCR, western blotting, and pharmacological inhibition tests revealed that US10 is mainly transcribed in the late stage of viral replication. However, the presence of the DNA polymerase inhibitor ganciclovir and the protein synthesis inhibitor cycloheximide blocked transcription. Therefore, US10 is a γ2 (true late) gene. Indirect immunofluorescence analysis showed that US10 proteins were initially diffusely distributed throughout the cytoplasm, but with the passage of time, they gradually relocated to a perinuclear region. The US10 protein was detected in purified DEV virions by mass spectrometry, but was not detected by western blotting, indicating that DEV US10 is a minor virion protein.

CONCLUSIONS

The DEV US10 gene is a γ2 gene and the US10 protein is localized in the perinuclear region. DEV US10 is a virion component.

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.

The pregenome/C RNA of duck hepatitis B virus is not used for translation of core protein during the early phase of infection in vitro

Over the course of duck hepatitis B virus (DHBV) replication, one type of RNA (pregenome/C RNA, 3.5 kb) that corresponds to the whole genome of DHBV is generated from the transcription of viral cccDNA. Previous work has proposed three functions for the pregenome/C RNA: it can serve as the pregenome and be packaged into the core protein during the process of replication, and it encodes the mRNA for both the capsid protein and the viral polymerase. However, little is known about the timing of these functions during the different stages of viral infection. In this study, a reverse transcription quantitative real-time PCR assay was developed to analyze the dynamic transcription process of the pregenome/C RNA. The dynamic expression of the core protein was investigated using an indirect immunofluorescence assay (IFA) and by western blot analysis. The generation of pregenome/C RNA began at 12 h post infection and peaked at 20 h post infection; however, the core protein was not detectable until 24h post infection. These results demonstrate that the core protein appeared approximately 12h later than the pregenome/C RNA. These results suggest that the DHBV pregenome/C RNA is not used for the translation of the viral core protein during the early stages of infection.

The transcription analysis of duck enteritis virus UL49.5 gene using real-time quantitative reverse transcription PCR

Duck enteritis virus (DEV) UL49.5 encoding glycoprotein N was a conserved gene. The transcription dynamic process of UL49.5 homologous genes in herpesviruses was reported. However, the transcription dynamic process of DEV UL49.5 gene has not yet been established. In this study, a real-time quantitative reverse transcription PCR (real-time qRT-PCR) assay was established to test the transcription dynamic process of DEV UL49.5 gene, and the recombinant plasmid pUCm-T/UL49.5 was constructed as the standard DNA. The samples prepared from DEV-infected (at different time points) and uninfected cell were detected and calculated. The results demonstrated that the real-time qRT-PCR assay was successfully established. The transcription product of DEV UL49.5 gene was first detected at 0.5 h post infection (p.i.), increased at 8 h p.i. and reached a peak at 60 h p.i. Our results illustrated that DEV UL49.5 gene could be regarded as a late gene. The transcription dynamic process of DEV UL49.5 gene may provide a significant clue for further studies of DEV UL49.5 gene.