Fine structure and morphogenesis of Borna disease virus

Avian Bornavirus Research—A Comprehensive Review

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.

ICTV Virus Taxonomy Profile: Bornaviridae

Members of the family Bornaviridae produce enveloped virions containing a linear negative-sense non-segmented RNA genome of about 9 kb. Bornaviruses are found in mammals, birds, reptiles and fish. The most-studied viruses with public health and veterinary impact are Borna disease virus 1 and variegated squirrel bornavirus 1, both of which cause fatal encephalitis in humans. Several orthobornaviruses cause neurological and intestinal disorders in birds, mostly parrots. Endogenous bornavirus-like sequences occur in the genomes of various animals. This is a summary of the International Committee on Taxonomy of Viruses (ICTV) Report on the family Bornaviridae, which is available at ictv.global/report/bornaviridae.

A New Multiplex Real-Time RT-PCR for Simultaneous Detection and Differentiation of Avian Bornaviruses

Avian bornaviruses were first described in 2008 as the causative agents of proventricular dilatation disease (PDD) in parrots and their relatives (Psittaciformes). To date, 15 genetically highly diverse avian bornaviruses covering at least five viral species have been discovered in different bird orders. Currently, the primary diagnostic tool is the detection of viral RNA by conventional or real-time RT-PCR (rRT-PCR). One of the drawbacks of this is the usage of either specific assays, allowing the detection of one particular virus, or of assays with a broad detection spectrum, which, however, do not allow for the simultaneous specification of the detected virus. To facilitate the simultaneous detection and specification of avian bornaviruses, a multiplex real-time RT-PCR assay was developed. Whole-genome sequences of various bornaviruses were aligned. Primers were designed to recognize conserved regions within the overlapping X/P gene and probes were selected to detect virus species-specific regions within the target region. The optimization of the assay resulted in the sensitive and specific detection of bornaviruses of Psittaciformes, Passeriformes, and aquatic birds. Finally, the new rRT-PCR was successfully employed to detect avian bornaviruses in field samples from various avian species. This assay will serve as powerful tool in epidemiological studies and will improve avian bornavirus detection.

Patterns of virus growth across the diversity of life

Although viruses in their natural habitats add up to less than 10% of the biomass, they contribute more than 90% of the genome sequences [1]. These viral sequences or 'viromes' encode viruses that populate the Earth's oceans [2, 3] and terrestrial environments [4, 5], where their infections impact life across diverse ecological niches and scales [6, 7], including humans [8-10]. Most viruses have yet to be isolated and cultured [11-13], and surprisingly few efforts have explored what analysis of available data might reveal about their nature. Here, we compiled and analyzed seven decades of one-step growth and other data for viruses from six major families, including their infections of archaeal, bacterial and eukaryotic hosts [14-191]. We found that the use of host cell biomass for virus production was highest for archaea at 10%, followed by bacteria at 1% and eukarya at 0.01%, highlighting the degree to which viruses of archaea and bacteria exploit their host cells. For individual host cells, the yield of virus progeny spanned a relatively narrow range (10-1000 infectious particles per cell) compared with the million-fold difference in size between the smallest and largest cells. Furthermore, healthy and infected host cells were remarkably similar in the time they needed to multiply themselves or their virus progeny. Specifically, the doubling time of healthy cells and the delay time for virus release from infected cells were not only correlated (r = 0.71, p < 10-10, n = 101); they also spanned the same range from tens of minutes to about a week. These results have implications for better understanding the growth, spread and persistence of viruses in complex natural habitats that abound with diverse hosts, including humans and their associated microbes.

Targeting histone epigenetics to control viral infections

During the past decades, many studies have significantly broadened our understanding of complex virus-host interactions to control chromatin structure and dynamics.1, 2 However, the role and impact of such modifications during viral infections is not fully revealed. Indeed, this type of regulation is bidirectional between the virus and the host. While viral replication and gene expression are significantly impacted by histone modifications on the viral chromatin,³ studies have shown that some viral pathogens dynamically manipulate cellular epigenetic factors to enhance their own survival and pathogenesis, as well as escape the immune system defense lines.⁴ In this dynamic, histone posttranslational modifications (PTMs) appear to play fundamental roles in the regulation of chromatin structure and recruitment of other factors.⁵ Genuinely, those PTMs play a vital role in lytic infection, latency reinforcement, or, conversely, viral reactivation.⁶ In this chapter, we will examine and review the involvement of histone modifications as well as their potential manipulation to control infections during various viral life cycle stages, highlighting their prospective implications in the clinical management of human immunodeficiency virus (HIV), herpes simplex virus (HSV), human cytomegalovirus (HCMV), hepatitis B and C viruses (HBV and HCV, respectively), Epstein–Barr virus (EBV), and other viral diseases. Targeting histone modifications is critical in setting the treatment of chronic viral infections with both lytic and latent stages (HIV, HCMV, HSV, RSV), virus-induced cancers (HBV, HCV, EBV, KSHV, HPV), and epidemic/emerging viruses (e.g. influenza virus, arboviruses).

Degradation of amyloid β peptide by neprilysin expressed from Borna disease virus vector

Accumulation of amyloid β (Aβ40 and Aβ42) in the brain is a characteristic of Alzheimer's disease (AD). Because neprilysin (NEP) is a major Aβ-degrading enzyme, NEP delivery in the brain is a promising gene therapy for AD. Borna disease virus (BoDV) vector enables long-term transduction of foreign genes in the central nerve system. Here, we evaluated the proteolytic ability of NEP transduced by the BoDV vector and found that the amounts of Aβ40 and Aβ42 significantly decreased, which suggests that NEP expressed from the BoDV vector is functional to degrade Aβ.

Dual function of the nuclear export signal of the Borna disease virus nucleoprotein in nuclear export activity and binding to viral phosphoprotein

BACKGROUND

Borna disease virus (BoDV), which has a negative-sense, single-stranded RNA genome, causes persistent infection in the cell nucleus. The nuclear export signal (NES) of the viral nucleoprotein (N) consisting of leucine at positions 128 and 131 and isoleucine at positions 133 and 136 overlaps with one of two predicted binding sites for the viral phosphoprotein (P). A previous study demonstrated that higher expression of BoDV-P inhibits nuclear export of N; however, the function of N NES in the interaction with P remains unclear. We examined the subcellular localization, viral polymerase activity, and P-binding ability of BoDV-N NES mutants. We also characterized a recombinant BoDV (rBoDV) harboring an NES mutation of N.

RESULTS

BoDV-N with four alanine-substitutions in the leucine and isoleucine residues of the NES impaired its cytoplasmic localization and abolished polymerase activity and P-binding ability. Although an alanine-substitution at position 131 markedly enhanced viral polymerase activity as determined by a minigenome assay, rBoDV harboring this mutation showed expression of viral RNAs and proteins relative to that of wild-type rBoDV.

CONCLUSIONS

Our results demonstrate that BoDV-N NES has a dual function in BoDV replication, i.e., nuclear export of N and an interaction with P, affecting viral polymerase activity in the nucleus.

Surface glycoprotein of Borna disease virus mediates virus spread from cell to cell

Borna disease virus (BDV) is a non-segmented negative-stranded RNA virus that maintains a strictly neurotropic and persistent infection in affected end hosts. The primary target cells for BDV infection are brain cells, e.g. neurons and astrocytes. The exact mechanism of how infection is propagated between these cells and especially the role of the viral glycoprotein (GP) for cell-cell transmission, however, are still incompletely understood. Here, we use different cell culture systems, including rat primary astrocytes and mixed cultures of rat brain cells, to show that BDV primarily spreads through cell-cell contacts. We employ a highly stable and efficient peptidomimetic inhibitor to inhibit the furin-mediated processing of GP and demonstrate that cleaved and fusion-active GP is strictly necessary for the cell-to-cell spread of BDV. Together, our quantitative observations clarify the role of Borna disease virus-glycoprotein for viral dissemination and highlight the regulation of GP expression as a potential mechanism to limit viral spread and maintain persistence. These findings furthermore indicate that targeting host cell proteases might be a promising approach to inhibit viral GP activation and spread of infection.

Borna disease virus infection in cats

Bornaviruses are known to cause neurological disorders in a number of animal species. Avian Bornavirus (ABV) causes proventricular dilatation disease (PDD) in birds and Borna disease virus (BDV) causes Borna disease in horses and sheep. BDV also causes staggering disease in cats, characterised by ataxia, behavioural changes and loss of postural reactions. BDV-infection markers in cats have been reported throughout the world. This review summarizes the current knowledge of Borna disease viruses in cats, including etiological agent, clinical signs, pathogenesis, epidemiology and diagnostics, with comparisons to Bornavirus infections in other species.

Epidemiology and host spectrum of Borna disease virus infections

Borna disease virus (BDV) has gained lot of interest because of its zoonotic potential, ability to introduce cDNA of its RNA transcripts into host genomes, and ability to cause severe neurobehavioural diseases. Classical Borna disease is a progressive meningoencephalomyelitis in horses and sheep, known in central Europe for centuries. According to current knowledge, BDV or a close relative also infects several other species, including humans at least occasionally, in central Europe and elsewhere, but the existence of potential 'human Borna disease' with its suspected neuropsychiatric symptoms is highly controversial. The recent detection of endogenized BDV-like genes in primate and various other vertebrate genomes confirms that at least ancient bornaviruses did infect our ancestors. The epidemiology of BDV is largely unknown, but accumulating evidence indicates vectors and reservoirs among small wild mammals. The aim of this review is to bring together the current knowledge on epidemiology of BDV infections. Specifically, geographical and host distribution are addressed and assessed in the critical light of the detection methods used. We also review some salient clinical aspects.

Model membrane platforms for biomedicine: case study on antiviral drug development

As one of the most important interfaces in cellular systems, biological membranes have essential functions in many activities such as cellular protection and signaling. Beyond their direct functions, they also serve as scaffolds to support the association of proteins involved in structural support, adhesion, and transport. Unfortunately, biological processes sometimes malfunction and require therapeutic intervention. For those processes which occur within or upon membranes, it is oftentimes difficult to study the mechanism in a biologically relevant, membranous environment. Therefore, the identification of direct therapeutic targets is challenging. In order to overcome this barrier, engineering strategies offer a new approach to interrogate biological activities at membrane interfaces by analyzing them through the principles of the interfacial sciences. Since membranes are complex biological interfaces, the development of simplified model systems which mimic important properties of membranes can enable fundamental characterization of interaction parameters for such processes. We have selected the hepatitis C virus (HCV) as a model viral pathogen to demonstrate how model membrane platforms can aid antiviral drug discovery and development. Responsible for generating the genomic diversity that makes treating HCV infection so difficult, viral replication represents an ideal step in the virus life cycle for therapeutic intervention. To target HCV genome replication, the interaction of viral proteins with model membrane platforms has served as a useful strategy for target identification and characterization. In this review article, we demonstrate how engineering approaches have led to the discovery of a new functional activity encoded within the HCV nonstructural 5A protein. Specifically, its N-terminal amphipathic, α-helix (AH) can rupture lipid vesicles in a size-dependent manner. While this activity has a number of exciting biotechnology and biomedical applications, arguably the most promising one is in antiviral medicine. Based on the similarities between lipid vesicles and the lipid envelopes of virus particles, experimental findings from model membrane platforms led to the prediction that a range of medically important viruses might be susceptible to rupturing treatment with synthetic AH peptide. This hypothesis was tested and validated by molecular virology studies. Broad-spectrum antiviral activity of the AH peptide has been identified against HCV, HIV, herpes simplex virus, and dengue virus, and many more deadly pathogens. As a result, the AH peptide is the first in class of broad-spectrum, lipid envelope-rupturing antiviral agents, and has entered the drug pipeline. In summary, engineering strategies break down complex biological systems into simplified biomimetic models that recapitulate the most important parameters. This approach is particularly advantageous for membrane-associated biological processes because model membrane platforms provide more direct characterization of target interactions than is possible with other methods. Consequently, model membrane platforms hold great promise for solving important biomedical problems and speeding up the translation of biological knowledge into clinical applications.

Borna disease virus infection perturbs energy metabolites and amino acids in cultured human oligodendroglia cells

Background

Borna disease virus is a neurotropic, non-cytolytic virus that has been widely employed in neuroscientific research. Previous studies have revealed that metabolic perturbations are associated with Borna disease viral infection. However, the pathophysiological mechanism underlying its mode of action remains unclear.

Methodology

Human oligodendroglia cells infected with the human strain Borna disease virus Hu-H1 and non-infected matched control cells were cultured in vitro. At day 14 post-infection, a proton nuclear magnetic resonance-based metabonomic approach was used to differentiate the metabonomic profiles of 28 independent intracellular samples from Borna disease virus-infected cells (n = 14) and matched control cells (n = 14). Partial least squares discriminant analysis was performed to demonstrate that the whole metabonomic patterns enabled discrimination between the two groups, and further statistical testing was applied to determine which individual metabolites displayed significant differences between the two groups.

Findings

Metabonomic profiling revealed perturbations in 23 metabolites, 19 of which were deemed individually significant: nine energy metabolites (α-glucose, acetate, choline, creatine, formate, myo-inositol, nicotinamide adenine dinucleotide, pyruvate, succinate) and ten amino acids (aspartate, glutamate, glutamine, glycine, histidine, isoleucine, phenylalanine, threonine, tyrosine, valine). Partial least squares discriminant analysis demonstrated that the whole metabolic patterns enabled statistical discrimination between the two groups.

Conclusion

Borna disease viral infection perturbs the metabonomic profiles of several metabolites in human oligodendroglia cells cultured in vitro. The findings suggest that Borna disease virus manipulates the host cell’s metabolic network to support viral replication and proliferation.

Borna disease virus - fact and fantasy

The occasion of Brian Mahy's retirement as editor of Virus Research provides an opportunity to reflect on the work that led one of the authors (Lipkin) to meet him shortly after the molecular discovery and characterization of Borna disease virus in the late 1980s, and work with authors Briese and Hornig to investigate mechanisms of pathogenesis and its potential role in human disease. This article reviews the history, molecular biology, epidemiology, and pathobiology of bornaviruses.

Antigen tissue distribution of Avian bornavirus (ABV) in psittacine birds with natural spontaneous proventricular dilatation disease and ABV genotype 1 infection

Tissues of 10 psittacines from aviary 1 ("case birds") and 5 psittacines from different aviaries were investigated for the presence of Avian bornavirus (ABV) antigen by immunohistochemistry using a polyclonal serum specific for the viral nucleocapsid (N) protein. Seven of 10 case birds had clinical signs, and necropsy findings consistent with proventricular dilatation disease (PDD) while 3 case birds and the 5 birds from other aviaries did not exhibit signs and lesions of this disease. In birds with clinical signs of PDD, ABV antigen was largely limited to neuroectodermal cells including neurons, astroglia, and ependymal cells of the central nervous system, neurons of the peripheral nervous system, and adrenal cells. ABV antigen was present in the nuclei and cytoplasm of infected cells. In 2 case birds that lacked signs and lesions of PDD, viral antigen had a more widespread distribution and was present in nuclei and cytoplasm of epithelial cells of the alimentary and urogenital tract, retina, heart, skeletal muscle, and skin in addition to the mentioned neuroectodermal cells. ABV RNA was identified by reverse transcription polymerase chain reaction (RT-PCR) in tissues of all 7 case birds available for testing from aviary 1, including 4 birds with PDD lesions and the 3 birds without PDD lesions. Sequencing and phylogenetic analysis indicated the presence of ABV genotype 1 in all cases. Findings further substantiate a role of ABV in PDD of psittacine bird species.

RNA splicing in a new rhabdovirus from Culex mosquitoes

Among members of the order Mononegavirales, RNA splicing events have been found only in the family Bornaviridae. Here, we report that a new rhabdovirus isolated from the mosquito Culex tritaeniorhynchus replicates in the nuclei of infected cells and requires RNA splicing for viral mRNA maturation. The virus, designated Culex tritaeniorhynchus rhabdovirus (CTRV), shares a similar genome organization with other rhabdoviruses, except for the presence of a putative intron in the coding region for the L protein. Molecular phylogenetic studies indicated that CTRV belongs to the family Rhabdoviridae, but it is yet to be assigned a genus. Electron microscopic analysis revealed that the CTRV virion is extremely elongated, unlike virions of rhabdoviruses, which are generally bullet shaped. Northern hybridization confirmed that a large transcript (approximately 6,500 nucleotides [nt]) from the CTRV L gene was present in the infected cells. Strand-specific reverse transcription-PCR (RT-PCR) analyses identified the intron-exon boundaries and the 76-nt intron sequence, which contains the typical motif for eukaryotic spliceosomal intron-splice donor/acceptor sites (GU-AG), a predicted branch point, and a polypyrimidine tract. In situ hybridization exhibited that viral RNAs are primarily localized in the nucleus of infected cells, indicating that CTRV replicates in the nucleus and is allowed to utilize the host's nuclear splicing machinery. This is the first report of RNA splicing among the members of the family Rhabdoviridae.

Failure to detect borna disease virus antibody and RNA from peripheral blood mononuclear cells of psychiatric patients

OBJECTIVE

Borna disease virus (BDV) is a highly neurotropic agent causing various neuropsychiatric symptoms in animals. Over the past two decades, it has been suggested that BDV might be associated with human psychiatric diseases. We aimed to investigate whether BDV is associated with psychiatric patients in Korea.

METHODS

We recruited 60 normal controls and 198 psychiatric patients (98 patients with depressive disorder, 60 with schizophrenia, and 40 with bipolar disorder). We used an indirect immunofluorescence antibody (IFA) test for the BDV antibody and a real-time reverse transcriptase polymerase chain reaction (rRT-PCR) assay for p24 and p40 RNA from peripheral blood mononuclear cells (PBMCs).

RESULTS

Neither the BDV antibody nor p24, p40 RNA was detected in controls and patients groups.

CONCLUSION

Our results suggest that BDV might not be associated with psychiatric patients in Korea.

Role of Borna disease virus in neuropsychiatric illnesses: are we inching closer?

The biological cause of psychiatric illnesses continues to be under intense scrutiny. Among the various neurotropic viruses, Borna disease virus (BDV) is another virus that preferentially targets the neurons of the limbic system and has been shown to be associated with behavioural abnormalities. Presence of various BDV markers, including viral RNA, in patients with affective and mood disorders have triggered ongoing debate worldwide regarding its aetiopathogenic relationship. This article analyses its current state of knowledge and recent advances in diagnosis in order to prove or refute the association of BDV in causation of human neuropsychiatric disorders. This emerging viral causative association of behavioural disorders, which seems to be inching closer, has implication not only for a paradigm shift in the treatment and management of neuropsychiatric illnesses but also has an important impact on the public health systems.

Experimental induction of proventricular dilatation disease in cockatiels (Nymphicus hollandicus) inoculated with brain homogenates containing avian bornavirus 4

BACKGROUND

Proventricular dilatation disease (PDD) is a fatal disorder of psittacine birds worldwide. The disease is characterized by lymphoplasmacytic infiltration of the central and peripheral nervous systems, leading to gastrointestinal motility and/or central nervous system dysfunction. Recently, we detected a significant association between avian bornavirus (ABV) infection and clinical signs of PDD in psittacines. However, it remains unclear whether ABV infection actually causes PDD. To address this question, we examined the impact of ABV inoculation on the cockatiel (Nymphicus hollandicus).

RESULTS

Five cockatiels were inoculated via multiple routes (intramuscular, intraocular, intranasal, and oral) with a brain homogenate derived from either a PDD(+) avian bornavirus 4 (ABV4) (+) case (n = 3 inoculees) or from a PDD(-) ABV(-) control (n = 2 inoculees). The control birds remained free of clinical or pathological signs of PDD, and tested ABV(-) by RT-PCR and immunohistochemistry (IHC). In contrast, all three cockatiels inoculated with ABV4(+) brain homogenate developed gross and microscopic PDD lesions, and two exhibited overt clinical signs. In numerous tissues, ABV RT-PCR and sequence analysis demonstrated the presence of ABV4 RNA nearly identical to that in the inoculum. ABV was detected in the central nervous system of the three ABV-inoculees by IHC. Pyrosequencing to investigate the viral flora in the ABV4(+) inoculum uncovered 7 unique reads sharing 73-100% nucleotide sequence identity with previously identified ABV sequences and 24 reads sharing 40-89% amino acid sequence identity with viruses in the Retroviridae and Astroviridae families. Of these candidate viral species, only ABV RNA was recovered from tissues of the inoculated birds.

CONCLUSION

In this study, the clinical and pathological manifestations of PDD were induced by inoculation of cockatiels with brain homogenates containing avian bornavirus 4. By using high throughput pyrosequencing an in-depth view of the viral content of the inoculum was achieved, revealing that of 3 candidate virus families detected, only the presence of ABV RNA correlated with the development of PDD. This study provides evidence of a causal association between ABV4 infection and PDD in cockatiels.

Structural comparisons of the nucleoprotein from three negative strand RNA virus families

Structures of the nucleoprotein of three negative strand RNA virus families, borna disease virus, rhabdovirus and influenza A virus, are now available. Structural comparisons showed that the topology of the RNA binding region from the three proteins is very similar. The RNA was shown to fit into a cavity formed by the two distinct domains of the RNA binding region in the rhabdovirus nucleoprotein. Two helices connecting the two domains characterize the center of the cavity. The nucleoproteins contain at least 5 conserved helices in the N-terminal domain and 3 conserved helices in the C-terminal domain. Since all negative strand RNA viruses are required to have the ribonucleoprotein complex as their active genomic templates, it is perceivable that the (5H+3H) structure is a common motif in the nucleoprotein of negative strand RNA viruses.

Reverse-genetic approaches to the study of Borna disease virus

Borna disease virus (BDV) is an enveloped virus that has a non-segmented, negative-strand RNA genome with the characteristic organization of the mononegaviruses. However, based on its unique genetic and biological features, BDV is considered to be the prototypic member of a new mononegavirus family, the Bornaviridae. BDV causes central nervous system (CNS) disease in a wide variety of mammals. This article discusses the recently developed reverse-genetics systems for BDV, and the implications for the elucidation of the molecular mechanisms underlying BDV-host interactions, including the basis of BDV persistence in the CNS and its associated diseases.

Maturation of Borna disease virus glycoprotein

The maturation of Borna disease virus (BDV) glycoprotein GP was studied in regard to intracellular compartmentalization, compartmentalization signal-domains, proteolytic processing, and packaging into virus particles. Our data show that BDV-GP is (i) predominantly located in the endoplasmic reticulum (ER), (ii) partially exists in the ER already as cleaved subunits GP-N and GP-C, (iii) is directed to the ER/cis-Golgi region by its transmembrane and/or cytoplasmic domains in CD8-BDV-GP hybrid constructs and (iv) is incorporated in the virus particles as authentic BDV glycoprotein exclusively in the cleaved form decorated with N-glycans of the complex type. Downregulation of BDV-glycoproteins on the cell surface, their limited proteolytic processing, and protection of antigenic epitopes on the viral glycoproteins by host-identical N-glycans are different strategies for persistent virus infections.

Borna disease virus glycoprotein is required for viral dissemination in neurons

Borna disease virus (BDV) is a nonsegmented negative-strand RNA virus with a tropism for neurons. Infection with BDV causes neurological diseases in a wide variety of animal species. Although it is known that the virus spreads from neuron to neuron, assembled viral particles have never been visualized in the brains of infected animals. This has led to the hypothesis that BDV spreads as nonenveloped ribonucleoproteins (RNP) rather than as enveloped viral particles. We assessed whether the viral envelope glycoprotein (GP) is required for neuronal dissemination of BDV by using primary cultures of rat hippocampal neurons. We show that upon in vitro infection, BDV replicated and spread efficiently in this system. Despite rapid virus dissemination, very few infectious viral particles were detectable in the culture. However, neutralizing antibodies directed against BDV-GP inhibited BDV spread. In addition, interference with BDV-GP processing by inhibiting furin-mediated cleavage of the glycoprotein blocked virus spread. Finally, antisense treatment with peptide nucleic acids directed against BDV-GP mRNA inhibited BDV dissemination, marking BDV-GP as an attractive target for antiviral therapy against BDV. Together, our results demonstrate that the expression and correct processing of BDV-GP are necessary for BDV dissemination in primary cultures of rat hippocampal neurons, arguing against the hypothesis that the virus spreads from neuron to neuron in the form of nonenveloped RNP.

Borna disease virus nucleoprotein interacts with the CDC2-cyclin B1 complex

Transition from G(2) to M phase, a cell cycle checkpoint, is regulated by the Cdc2-cyclin B1 complex. Here, we report that persistent infection with Borna disease virus (BDV), a noncytolytic RNA virus infecting the central nervous system, results in decelerated proliferation of infected host cells due to a delayed G(2)-to-M transition. Persistent BDV-infected rat fibroblast cells showed reduced proliferation compared to uninfected cells. In pull-down assays we observed an interaction of the viral nucleoprotein with the Cdc2-cyclin B1 complex. Transfection of the viral nucleoprotein but not of the phosphoprotein also results in decelerated proliferation. This phenomenon was found in BDV-susceptible primary rat fibroblast cells and also in primary mouse cells, which are not susceptible to BDV infection. This is the first evidence that the noncytolytic Borna disease virus can manipulate host cell functions via interaction of the viral nucleoprotein with mitotic entry regulators. BDV preferentially infects and persists in nondividing neurons. The present report could give an explanation for this selective choice of host cell by BDV.

Bornavirus and the brain

Borna disease virus (BDV) causes central nervous system (CNS) disease that is frequently manifested by behavioral abnormalities. BDV is a nonsegmented, negative, single-stranded RNA virus. On the basis of its unique genetic and biologic features, BDV is the prototypic member of a new virus family, Bornaviridae, within the order Mononegavirales. Therefore, the investigation of the molecular and cell biology of BDV may provide new insights about virus-cell interactions in the CNS. BDV is an important model system for the investigation of viral persistence in the CNS. Serologic and molecular epidemiologic studies suggest that BDV can infect humans. Despite controversy about potential association with human neuropsychiatric illnesses, BDV affords an intriguing model for the study of these illnesses. Neonatal BDV-infected rats display neurodevelopmental, physiologic, and neurobehavioral abnormalities that closely parallel some of the main features associated with several human mental disorders.

Identification of the amino terminal subunit of the glycoprotein of Borna disease virus

The only surface membrane glycoprotein of Borna disease virus (BDV) is synthesized as a polypeptide with a molecular mass of 57 kDa and N-glycosylated to a precursor glycoprotein (GP) of about 94 kDa. It is processed by the cellular protease furin into the C-terminal membrane-anchored subunit GP-C, also known as gp43, and a presumptive N-terminal subunit GP-N, that is highly glycosylated and has a molecular mass of about 51 kDa. However, up to now the latter remained undetected in BDV-infected material. We describe a novel approach to identify glycan masked linear antigenic epitopes. In the present study, GP-N was identified in BDV-infected cells by a combination of lectin precipitation, enzymatic deglycosylation on blot and immunochemistry using an N-terminal specific antiserum. The GP-N has an apparent molecular mass of 45-50 kDa in its glycosylated form and 27 kDa in its deglycosylated form. N-glycan analysis revealed that the precursor GP contains only mannose-rich N-glycans, whereas GP-N and GP-C contain mannose-rich and complex-type N-glycans.

Open reading frame III of borna disease virus encodes a nonglycosylated matrix protein

The open reading frame III of Borna disease virus (BDV) codes for a protein with a mass of 16 kDa, named p16 or BDV-M. p16 was described as an N-glycosylated protein in several previous publications and therefore was termed gp18, although the amino acid sequence of p16 does not contain any regular consensus sequence for N glycosylation. We examined glycosylation of p16 and studied its membrane topology using antisera raised against peptides, which comprise the N and the C termini. Neither an N- nor a C-terminal peptide is cleaved from p16 during maturation. Neither deglycosylation of p16 by endoglycosidases nor binding of lectin to p16 was detectable. Introduction of typical N-glycosylation sites at the proposed sites of p16 failed in carbohydrate attachment. Flotation experiments with membranes of BDV-infected cells on density gradients revealed that p16 is not an integral membrane protein, since it can be dissociated from membranes. Our experimental data strongly suggest that p16 is a typical nonglycosylated matrix protein associated at the inner surface of the viral membrane, as is true for homologous proteins of other members of the Mononegavirales order.

Search for Borna disease virus in Danish fibromyalgia patients

OBJECTIVE

The purpose of this study was to look for Borna disease virus (BDV) in 18 patients with acute onset of fibromyalgia (FMS) following a "flu-like" episode. BDV is a neurotropic RNA virus affecting horses and sheep. Infections in animals have been reported to cause immune mediated disease characterized by abnormalities in behavior. A possible link between BDV and neuropsychiatric diseases in man has been described, and lately a connection to chronic fatigue syndrome (CFS) has been suggested.

METHODS

A BDV-specific nested PCR (RT-PCR) was performed on serum and spinal fluid.

RESULTS

The BDV genome was not detected in any of the FMS cases.

CONCLUSION

Although BDV was not demonstrated in spinal fluid or serum from the tested patients with FMS, we believe that it is important to report our results, since FMS can exhibit many manifestations in common with CFS. Possible reasons for the discrepant findings are discussed.

Borna disease virus: a mystery as an emerging zoonotic pathogen

For Central European veterinarians, Borna disease (BD) has been known for a long time as a sporadically occurring, progressive viral polioencephalomyelitis predominantly affecting horses and sheep and-as discovered in the last decade-an increasing number of domestic and zoo animals. The aetiological agent, the Borna disease virus (BDV), a negative-sense, single-stranded RNA virus classified in the new virus family Bornaviridae within the order Mononegavirales, can induce severe clinical signs typically of a viral encephalitis with striking behavioural disturbances. After an incubation period lasting a few weeks to several months, BDV-infection causes locomotor and sensory dysfunctions followed by paralysis and death. Natural infections seem to be subclinical in most cases. BD received world-wide attention when it was reported that sera and/or cerebrospinal fluids from neuro-psychiatric patients can contain BDV-specific antibodies. Since infected animals produce BDV-specific antibodies only after virus replication, it was assumed that the broad spectrum of BDV-susceptible species also includes man. However, reports describing the presence of other BDV-markers, i.e. BDV-RNA or BDV-antigen, in peripheral blood leukocytes or brain tissue of neuro-psychiatric patients are highly controversial and, therefore, the role of BDV in human neuro-psychiatric disorders is questionable. (c) 2001 Harcourt Publishers Ltd.

Borna disease in horses

Borna disease is a sporadically occurring, progressive viral polioencephalomyelitis that primarily affects horses and sheep. The etiological agent, Borna disease virus (BDV), is an enveloped, single-stranded RNA virus that has been classified in the new virus family Bornaviridae within the order Mononegavirales. Serological evidence of BDV infection has been found in an increasing number of countries throughout the world. After an incubation period lasting a few weeks to several months, BDV infection can cause locomotor and sensory dysfunction followed by paralysis and death. Borna disease is the result of a virus-induced immunopathological reaction. BDV-specific antibodies and viral RNA have been found in humans with various psychiatric disorders.

Contrast-enhanced immunoelectron microscopy for Helicobacter pylori

Since a method of contrast enhancement for immunoelectron microscopy has not been available in bacteriology, the morphological localization of proteins of Helicobacter pylori is not well known. In this report, we established a method of contrast enhancement in immunoelectron microscopy in this organism. Immunostained ultrathin sections are stained with a mixture of alcian blue and osmium tetroxide prior to staining with uranyl acetate. This method of staining provided good contrast enhancement of the bacterial cell wall and membrane without any loss of immunolabeled gold particles on the ultrathin section.