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Komorizono R, Fujino K, Kessler S, Runge S, Kanda T, Horie M, Makino A, Rubbenstroth D, Tomonaga K. Reverse genetics of parrot bornavirus 4 reveals a unique splicing of the glycoprotein gene that affects viral propagation. J Virol 2023; 97:e0050923. [PMID: 37578232 PMCID: PMC10506466 DOI: 10.1128/jvi.00509-23] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 04/08/2023] [Accepted: 06/27/2023] [Indexed: 08/15/2023] Open
Abstract
Viruses can utilize host splicing machinery to enable the expression of multiple genes from a limited-sized genome. Orthobornaviruses use alternative splicing to regulate the expression level of viral proteins and achieve efficient viral replication in the nucleus. Although more than 20 orthobornaviruses have been identified belonging to eight different viral species, virus-specific splicing has not been demonstrated. Here, we demonstrate that the glycoprotein (G) transcript of parrot bornavirus 4 (PaBV-4; species Orthobornavirus alphapsittaciforme), a highly virulent virus in psittacines, undergoes mRNA splicing and expresses a soluble isoform termed sGP. Interestingly, the splicing donor for sGP is not conserved in other orthobornaviruses, including those belonging to the same orthobornavirus species, suggesting that this splicing has evolved as a PaBV-4-specific event. We have also shown that exogenous expression of sGP does not affect PaBV-4 replication or de novo virion infectivity. In this study, to investigate the role of sGP in viral replication, we established a reverse genetics system for PaBV-4 by using avian cell lines and generated a recombinant virus lacking the spliced mRNA for sGP. Using the recombinant viruses, we show that the replication of the sGP-deficient virus is significantly slower than that of the wild-type virus and that the exogenous expression of sGP cannot restore its propagation efficiency. These results suggest that autologous or controlled expression of sGP by splicing may be important for PaBV-4 propagation. The reverse genetics system for avian bornaviruses developed here will be a powerful tool for understanding the replication strategies and pathogenesis of avian orthobornaviruses. IMPORTANCE Parrot bornavirus 4 (PaBV-4) is the dominant cause of proventricular dilatation disease, a severe gastrointestinal and central nervous system disease among avian bornaviruses. In this study, we discovered that PaBV-4 expresses a soluble isoform of glycoprotein (G), called sGP, through alternative splicing of the G mRNA, which is unique to this virus. To understand the role of sGP in viral replication, we generated recombinant PaBV-4 lacking the newly identified splicing donor site for sGP using a reverse genetics system and found that its propagation was significantly slower than that of the wild-type virus, suggesting that sGP plays an essential role in PaBV-4 infection. Our results provide important insights not only into the replication strategy but also into the pathogenesis of PaBV-4, which is the most prevalent bornavirus in captive psittacines worldwide.
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Affiliation(s)
- Ryo Komorizono
- Laboratory of RNA Viruses, Department of Virus Research, Institute for Life and Medical Sciences (LiMe), Kyoto University, Kyoto, Japan
| | - Kan Fujino
- Laboratory of Microbiology, School of Veterinary Medicine, Azabu University, Kanagawa, Japan
- Institute of Virology, Medical Centre - University of Freiburg, Freiburg, Germany
| | - Susanne Kessler
- Institute of Virology, Medical Centre - University of Freiburg, Freiburg, Germany
| | - Solveig Runge
- Institute of Virology, Medical Centre - University of Freiburg, Freiburg, Germany
| | - Takehiro Kanda
- Laboratory of RNA Viruses, Department of Virus Research, Institute for Life and Medical Sciences (LiMe), Kyoto University, Kyoto, Japan
- Department of Molecular Virology, Graduate School of Medicine, Kyoto University, Kyoto, Japan
| | - Masayuki Horie
- Laboratory of RNA Viruses, Department of Virus Research, Institute for Life and Medical Sciences (LiMe), Kyoto University, Kyoto, Japan
- Hakubi Center for Advanced Research, Kyoto University, Kyoto, Japan
| | - Akiko Makino
- Laboratory of RNA Viruses, Department of Virus Research, Institute for Life and Medical Sciences (LiMe), Kyoto University, Kyoto, Japan
- Laboratory of RNA Viruses, Department of Mammalian Regulatory Network, Graduate School of Biostudies, Kyoto University, Kyoto, Japan
| | - Dennis Rubbenstroth
- Institute of Virology, Medical Centre - University of Freiburg, Freiburg, Germany
- Institute of Diagnostic Virology, Friedrich-Loeffler-Institut, Greifswald - Insel, Riems, Germany
| | - Keizo Tomonaga
- Laboratory of RNA Viruses, Department of Virus Research, Institute for Life and Medical Sciences (LiMe), Kyoto University, Kyoto, Japan
- Department of Molecular Virology, Graduate School of Medicine, Kyoto University, Kyoto, Japan
- Laboratory of RNA Viruses, Department of Mammalian Regulatory Network, Graduate School of Biostudies, Kyoto University, Kyoto, Japan
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Rubbenstroth D. Avian Bornavirus Research—A Comprehensive Review. Viruses 2022; 14:v14071513. [PMID: 35891493 PMCID: PMC9321243 DOI: 10.3390/v14071513] [Citation(s) in RCA: 16] [Impact Index Per Article: 8.0] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 06/02/2022] [Revised: 06/30/2022] [Accepted: 07/05/2022] [Indexed: 02/01/2023] Open
Abstract
Avian bornaviruses constitute a genetically diverse group of at least 15 viruses belonging to the genus Orthobornavirus within the family Bornaviridae. After the discovery of the first avian bornaviruses in diseased psittacines in 2008, further viruses have been detected in passerines and aquatic birds. Parrot bornaviruses (PaBVs) possess the highest veterinary relevance amongst the avian bornaviruses as the causative agents of proventricular dilatation disease (PDD). PDD is a chronic and often fatal disease that may engulf a broad range of clinical presentations, typically including neurologic signs as well as impaired gastrointestinal motility, leading to proventricular dilatation. It occurs worldwide in captive psittacine populations and threatens private bird collections, zoological gardens and rehabilitation projects of endangered species. In contrast, only little is known about the pathogenic roles of passerine and waterbird bornaviruses. This comprehensive review summarizes the current knowledge on avian bornavirus infections, including their taxonomy, pathogenesis of associated diseases, epidemiology, diagnostic strategies and recent developments on prophylactic and therapeutic countermeasures.
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Affiliation(s)
- Dennis Rubbenstroth
- Institute of Diagnostic Virology, Friedrich-Loeffler-Institut, 17493 Greifswald, Insel Riems, Germany
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Optimal Expression of the Envelope Glycoprotein of Orthobornaviruses Determines the Production of Mature Virus Particles. J Virol 2021; 95:JVI.02221-20. [PMID: 33268525 PMCID: PMC8092845 DOI: 10.1128/jvi.02221-20] [Citation(s) in RCA: 3] [Impact Index Per Article: 1.0] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/24/2022] Open
Abstract
An RNA virus-based episomal vector (REVec) whose backbone is Borna disease virus 1 (BoDV-1) can provide long-term gene expression in transduced cells. To improve the transduction efficiency of REVec, we evaluated the role of the viral envelope glycoprotein (G) of the genus Orthobornavirus, including that of BoDV-1, in the production of infectious particles. By using G-pseudotype assay in which the lack of G in G-deficient REVec (ΔG-REVec) was compensated for expression of G, we found that excess expression of BoDV-1-G does not affect particle production itself but results in uncleaved and aberrant mature G expression in the cells, leading to the production of REVec particles with low transduction titers. We revealed that the expression of uncleaved G in the cells inhibits the incorporation of mature G and vgRNA into the particles. This feature of G was conserved among mammalian and avian orthobornaviruses; however, the cleavage efficacy of canary bornavirus 1 (CnBV-1)-G was exceptionally not impaired by its excess expression, which led to the production of the pseudotype ΔG-REVec with the highest titer. Chimeric G proteins between CnBV-1 and -2 revealed that the signal peptide of CnBV-1-G was responsible for the cleavage efficacy through the interaction with intracellular furin. We showed that CnBV-1 G leads to the development of pseudotyped REVec with high transduction efficiency and a high-titer recombinant REVec. Our study demonstrated that the restricted expression of orthobornavirus G contributes to the regulation of infectious particle production, the mechanism of which can improve the transduction efficiency of REVec.IMPORTANCE Most viruses causing persistent infection produce few infectious particles from the infected cells. Borna disease virus 1, a member of the genus Orthobornavirus, is an RNA virus that persistently infects the nucleus and has been applied to vectors for long-term gene expression. In this study, we showed that, common among orthobornaviruses, excessive G expression does not affect particle production itself but reduces the production of infectious particles with mature G and genomic RNA. This result suggested that limited G expression contributes to suppressing abnormal viral particle production. On the other hand, we found that canary bornavirus 1 has an exceptional G maturation mechanism and produces a high-titer virus. Our study will contribute to not only understanding the mechanism of infectious particle production but also improving the vector system of orthobornaviruses.
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Komorizono R, Sassa Y, Horie M, Makino A, Tomonaga K. Evolutionary Selection of the Nuclear Localization Signal in the Viral Nucleoprotein Leads to Host Adaptation of the Genus Orthobornavirus. Viruses 2020; 12:v12111291. [PMID: 33187187 PMCID: PMC7698282 DOI: 10.3390/v12111291] [Citation(s) in RCA: 3] [Impact Index Per Article: 0.8] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 10/20/2020] [Revised: 11/09/2020] [Accepted: 11/10/2020] [Indexed: 12/23/2022] Open
Abstract
Adaptation of the viral life cycle to host cells is necessary for efficient viral infection and replication. This evolutionary process has contributed to the mechanism for determining the host range of viruses. Orthobornaviruses, members of the family Bornaviridae, are non-segmented, negative-strand RNA viruses, and several genotypes have been isolated from different vertebrate species. Previous studies revealed that some genotypes isolated from avian species can replicate in mammalian cell lines, suggesting the zoonotic potential of avian orthobornaviruses. However, the mechanism by which the host specificity of orthobornaviruses is determined has not yet been identified. In this study, we found that the infectivity of orthobornaviruses is not determined at the viral entry step, mediated by the viral glycoprotein and matrix protein. Furthermore, we demonstrated that the nuclear localization signal (NLS) sequence in the viral nucleoprotein (N) has evolved under natural selection and determines the host-specific viral polymerase activity. A chimeric mammalian orthobornavirus, which has the NLS sequence of avian orthobornavirus N, exhibited a reduced propagation efficiency in mammalian cells. Our findings indicated that nuclear transport of the viral N is a determinant of the host range of orthobornaviruses, providing insights into the evolution and host adaptation of orthobornaviruses.
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Affiliation(s)
- Ryo Komorizono
- Laboratory of RNA Viruses, Department of Virus Research, Institute for Frontier Life and Medical Sciences, Kyoto University, Kyoto 606-8507, Japan; (R.K.); (M.H.)
- Laboratory of RNA Viruses, Department of Mammalian Regulatory Network, Graduate School of Biostudies, Kyoto University, Kyoto 606-8507, Japan
| | - Yukiko Sassa
- Laboratory of Veterinary Infectious Disease, Tokyo University of Agriculture and Technology, Tokyo 183-8509, Japan;
| | - Masayuki Horie
- Laboratory of RNA Viruses, Department of Virus Research, Institute for Frontier Life and Medical Sciences, Kyoto University, Kyoto 606-8507, Japan; (R.K.); (M.H.)
- Hakubi Center for Advanced Research, Kyoto University, Kyoto 606-8507, Japan
| | - Akiko Makino
- Laboratory of RNA Viruses, Department of Virus Research, Institute for Frontier Life and Medical Sciences, Kyoto University, Kyoto 606-8507, Japan; (R.K.); (M.H.)
- Laboratory of RNA Viruses, Department of Mammalian Regulatory Network, Graduate School of Biostudies, Kyoto University, Kyoto 606-8507, Japan
- Correspondence: (A.M.); (K.T.)
| | - Keizo Tomonaga
- Laboratory of RNA Viruses, Department of Virus Research, Institute for Frontier Life and Medical Sciences, Kyoto University, Kyoto 606-8507, Japan; (R.K.); (M.H.)
- Laboratory of RNA Viruses, Department of Mammalian Regulatory Network, Graduate School of Biostudies, Kyoto University, Kyoto 606-8507, Japan
- Department of Molecular Virology, Graduate School of Medicine, Kyoto University, Kyoto 606-8507, Japan
- Correspondence: (A.M.); (K.T.)
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Pham PH, Leacy A, Deng L, Nagy É, Susta L. Isolation of Ontario aquatic bird bornavirus 1 and characterization of its replication in immortalized avian cell lines. Virol J 2020; 17:16. [PMID: 32005267 PMCID: PMC6995091 DOI: 10.1186/s12985-020-1286-6] [Citation(s) in RCA: 9] [Impact Index Per Article: 2.3] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 06/24/2019] [Accepted: 01/20/2020] [Indexed: 11/10/2022] Open
Abstract
BACKGROUND Aquatic bird bornavirus 1 (ABBV-1) has been associated with neurological diseases in wild waterfowls. In Canada, presence of ABBV-1 was demonstrated by RT-qPCR and immunohistochemistry in tissues of waterfowls with history of neurological disease and inflammation of the central and peripheral nervous tissue, although causation has not been proven by pathogenesis experiments, yet. To date, in vitro characterization of ABBV-1 is limited to isolation in primary duck embryo fibroblasts. The objectives of this study were to describe isolation of ABBV-1 in primary duck embryonic fibroblasts (DEF), and characterize replication in DEF and three immortalized avian fibroblast cell lines (duck CCL-141, quail QT-35, chicken DF-1) in order to evaluate cellular permissivity and identify suitable cell lines for routine virus propagation. METHODS The virus was sequenced, and phylogenetic analysis performed on a segment of the N gene coding region. Virus spread in cell cultures, viral RNA and protein production, and titres were evaluated at different passages using immunofluorescence, RT-qPCR, western blotting, and tissue culture dose 50% (TCID50) assay, respectively. RESULTS The isolated ABBV-1 showed 97 and 99% identity to European ABBV-1 isolate AF-168 and North American ABBV-1 isolates 062-CQ and CG-N1489, and could infect and replicate in DEF, CCL-141, QT-35 and DF-1 cultures. Viral RNA was detected in all four cultures with highest levels observed in DEF and CCL-141, moderate in QT-35, and lowest in DF-1. N protein was detected in western blots from infected DEF, CCL-141 and QT-35 at moderate to high levels, but minimally in infected DF-1. Infectious titre was highest in DEF (between approximately 105 to 106 FFU / 106 cells). Regarding immortalized cell lines, CCL-141 showed the highest titre between approximately 104 to 105 FFU / 106 cells. DF-1 produced minimal infectious titre. CONCLUSIONS This study confirms the presence of ABBV-1 among waterfowl in Canada and reported additional in vitro characterization of this virus in different avian cell lines. ABBV-1 replicated to highest titre in DEF, followed by CCL-141 and QT-35, and poorly in DF-1. Our results showed that CCL-141 can be used instead of DEF for routine ABBV-1 production, if a lower titre is an acceptable trade-off for the simplicity of using immortalized cell line over primary culture.
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Affiliation(s)
- Phuc H Pham
- Department of Pathobiology, Ontario Veterinary College, University of Guelph, Guelph, ON, Canada
| | - Alexander Leacy
- Department of Pathobiology, Ontario Veterinary College, University of Guelph, Guelph, ON, Canada
| | - Li Deng
- Department of Pathology and Molecular Medicine, McMaster University, Hamilton, ON, Canada
| | - Éva Nagy
- Department of Pathobiology, Ontario Veterinary College, University of Guelph, Guelph, ON, Canada
| | - Leonardo Susta
- Department of Pathobiology, Ontario Veterinary College, University of Guelph, Guelph, ON, Canada.
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Development of a reverse transcription-loop-mediated isothermal amplification assay for the detection of parrot bornavirus 4. J Virol Methods 2019; 275:113749. [PMID: 31622637 DOI: 10.1016/j.jviromet.2019.113749] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 07/23/2019] [Revised: 09/21/2019] [Accepted: 10/08/2019] [Indexed: 10/25/2022]
Abstract
Avian bornavirus (ABV) is the causative agent of proventricular dilatation disease, which is fatal in psittacine birds. ABVs have spread worldwide, and outbreaks have led to mass deaths of captive birds in commercial and breeding facilities. The segregation of infected birds is a countermeasure to prevent ABV spread in aviaries. However, this approach requires a highly sensitive detection method for the screening of infected birds before virus transmission. In this study, we developed a reverse transcription-loop-mediated isothermal amplification (RT-LAMP) assay for the diagnosis of parrot bornavirus 4 (PaBV-4), a dominant ABV genotype. Using this assay, we successfully detected PaBV-4 RNA in cell cultures, brain tissues, and feces. We also developed methods for simple RNA extraction and visual detection without electrophoresis. The sensitivity of the newly established RT-LAMP assay was 100-fold higher than that of the real-time PCR (RT-qPCR) assay. Accordingly, the RT-LAMP assay developed in this study is suitable for the rapid and sensitive diagnosis of PaBV-4 without specialized equipment and will contribute to virus control in aviaries.
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Tokunaga T, Yamamoto Y, Sakai M, Tomonaga K, Honda T. Antiviral activity of favipiravir (T-705) against mammalian and avian bornaviruses. Antiviral Res 2017; 143:237-245. [DOI: 10.1016/j.antiviral.2017.04.018] [Citation(s) in RCA: 22] [Impact Index Per Article: 3.1] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 11/10/2016] [Revised: 04/28/2017] [Accepted: 04/28/2017] [Indexed: 01/18/2023]
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