Characterization of a calcium binding domain in the VP1 protein of the avian polyomavirus, budgerigar fledgling disease virus

Pathogenicity of Avian Polyomaviruses and Prospect of Vaccine Development

Polyomaviruses are nonenveloped icosahedral viruses with a double-stranded circular DNA containing approximately 5000 bp and 5–6 open reading frames. In contrast to mammalian polyomaviruses (MPVs), avian polyomaviruses (APVs) exhibit high lethality and multipathogenicity, causing severe infections in birds without oncogenicity. APVs are classified into 10 major species: Adélie penguin polyomavirus, budgerigar fledgling disease virus, butcherbird polyomavirus, canary polyomavirus, cormorant polyomavirus, crow polyomavirus, Erythrura gouldiae polyomavirus, finch polyomavirus, goose hemorrhagic polyomavirus, and Hungarian finch polyomavirus under the genus Gammapolyomavirus. This paper briefly reviews the genomic structure and pathogenicity of the 10 species of APV and some of their differences in terms of virulence from MPVs. Each gene’s genomic size, number of amino acid residues encoding each gene, and key biologic functions are discussed. The rationale for APV classification from the Polyomavirdae family and phylogenetic analyses among the 10 APVs are also discussed. The clinical symptoms in birds caused by APV infection are summarized. Finally, the strategies for developing an effective vaccine containing essential epitopes for preventing virus infection in birds are discussed. We hope that more effective and safe vaccines with diverse protection will be developed in the future to solve or alleviate the problems of viral infection.

Deterioration of eggshell quality is related to calbindin in laying hens infected with velogenic genotype VIId Newcastle disease virus

The aim of this study was to determine the mechanism by which Newcastle disease virus (NDV) affects eggshell quality. Thirty-week-old specific pathogen free (SPF) egg-laying hens were inoculated with the velogenic genotype VIId NDV strain (infected group) or with inoculating media without virus (control group) by combined intraocular and intranasal routes. The levels of CaBP-D28k mRNA expression in the uterus, a gene related to eggshell quality, were examined by quantitative reverse transcriptase polymerase chain reaction (RT-PCR). The quality of eggshells was analyzed by scanning electron microscopy (SEM). The infected group showed a marked decline in egg production when compared to the control group. The NDV antigen was found more abundantly in the glandular epithelium of the infected hens' uteri from 1 to 15 d post-inoculation (dpi). The levels of CaBP-D28k mRNA expression in the uteri of infected hens were significantly lower than in the control hens from 3 to 15 dpi (P < 0.05). The changes in the Ca concentrations in the eggshells were consistent with the expression of CaBP-D28k mRNA in the infected hens. Ultrastructural examination of eggshells showed significantly reduced shell thickness in the infected hens from 1 to 15 dpi (P < 0.05). Furthermore, obvious changes in the structure of the external shell surface and shell membrane were detected in the infected hens compared with the control hens. In conclusion, the current study confirmed that velogenic genotype VIId NDV infection is associated with the deterioration of the eggshell quality of the laying hens.

Production and biomedical applications of virus-like particles derived from polyomaviruses

Virus-like particles (VLPs), aggregates of capsid proteins devoid of viral genetic material, show great promise in the fields of vaccine development and gene therapy. These particles spontaneously self-assemble after heterologous expression of viral structural proteins. This review will focus on the use of virus-like particles derived from polyomavirus capsid proteins. Since their first recombinant production 27 years ago these particles have been investigated for a myriad of biomedical applications. These virus-like particles are safe, easy to produce, can be loaded with a broad range of diverse cargoes and can be tailored for specific delivery or epitope presentation. We will highlight the structural characteristics of polyomavirus-derived VLPs and give an overview of their applications in diagnostics, vaccine development and gene delivery.

Detection and sequence analysis of avian polyomavirus and psittacine beak and feather disease virus from psittacine birds in Taiwan

Avian polyomavirus (APV) and psittacine beak and feather disease virus (PBFDV) are the most common viral diseases of psittacine birds. In Taiwan, however, the existence of these viruses in psittacine birds has not been established. Polymerase chain reaction (PCR) methodology was therefore employed to ascertain whether APV and PBFDV genomes were present in isolates from psittacine birds of Taiwan. A total of 165 psittacine birds belonging to 22 genera were examined between 2002 and 2005. Findings revealed an APV-positive rate of 15.2%, a PBFDV-positive rate of 41.2%, and an APV/PBFDV dual infection rate of 10.3%. After cloning and sequencing, sequences of the PCR products were compared with sequences obtained from GenBank. For APV, the nucleotide identity among VP1 and t/T antigen coding regions ranged from 97.5% to 100% and 97.6% to 100%, respectively. For PBFDV, the nucleotide identity of ORF V1 and ORF C1 sequences ranged from 92.2% to 100% and 83.3% to 100%, respectively. The derived amino acid sequence alignment for PBFDV ORF V1 fragments revealed the conservation of two replication motifs and of the nucleotide binding site motif. In PBFDV, six of 42 deduced positions in the ORF C1 amino acid sequence were considered hypervariable. The established phylogenetic trees based on the four genome fragments examined in this study did not allow the assignment of particular APV or PBFDV nucleotide sequences to distinct avian species.

Interaction between molecules of hantavirus nucleocapsid protein

Intermolecular interactions of Tula hantavirus N (nucleocapsid) protein were detected in the yeast two-hybrid system, prompting further attempts to study this phenomenon. Using chemical cross-linking and immunoblotting it was shown that the N protein from purified virus and from infected cell lysates as well as recombinant protein produced in a baculovirus expression system are capable of forming dimers, trimers and multimers, thus confirming the capacity of the protein molecules to interact with each other. An ELISA format was developed in which molecules of the recombinant N protein were shown to associate non-covalently, via electrostatic interactions. Divalent cations (Ca(2+), Mn(2+), Mg(2+), Ba(2+)) enhanced the process 3- to 8-fold suggesting that adequate folding of the N protein is crucial for the association. Based on these data a model for hantavirus nucleocapsid assembly is proposed, in which N molecules first trimerize around the viral RNA molecule, and then the trimers gradually assemble forming longer multimers.

Avian polyomavirus major capsid protein VP1 interacts with the minor capsid proteins and is transported into the cell nucleus but does not assemble into capsid-like particles when expressed in the baculovirus system

The baculovirus system was used to construct and isolate AcMNPV-VP1, AcMNPV-VP2 and AcMNPV-VP3 recombinant viruses which express the respective avian polyomavirus (APV) structural proteins in Sf9 insect cells. These recombinant AcMNPVs containing APV structural protein genes were utilized to investigate protein-protein interactions between the structural proteins. Immunofluorescence studies utilizing Sf9 cells infected with the AcMNPV-VP1 revealed that the VP1 protein was expressed and localized in the cytoplasm and not transported into the nucleus. When the cells were co-infected with the VP1 and either VP2 or VP3 recombinant viruses, immunofluorescence of the VP1 protein was localized in the nucleus, indicating that the VP1 protein was transported to the nucleus by both the VP2 and VP3 minor proteins. This observation was suggestive of a protein-protein interaction between the expressed proteins. This protein-protein interaction was substantiated by laser scanning confocal microscopy of Sf9 cells that were co-infected with VP1, VP2 and VP3 recombinant viruses. However, the minor proteins could not be co-isolated with VP1 protein by immunoaffinity chromatography using a monoclonal anti-VP1 serum. In addition, capsid-like particles could not be purified either by CsC1 density gradient centrifugation or by immunoaffinity chromatography. VP1 capsomeres were isolated by immunoaffinity chromatography from Sf9 cells infected with AcMNPV-VP1, with or without the minor protein(s), and these capsomeres could assemble in vitro into capsid-like particles. Electron microscopic observation of thin-sectioned Sf9 cells, which were co-infected with VP1, VP2 and VP3 recombinant viruses, demonstrated capsomere-like structures in the nucleus, but capsid-like particles were not observed.