Sequence and genome organization of Borna disease virus

Negative-Strand RNA Virus-Vectored Vaccines

Vectored RNA vaccines offer a variety of possibilities to engineer targeted vaccines. They are cost-effective and safe, but replication competent, activating the humoral as well as the cellular immune system.This chapter focuses on RNA vaccines derived from negative-strand RNA viruses from the order Mononegavirales with special attention to Newcastle disease virus-based vaccines and their generation. It shall provide an overview on the advantages and disadvantages of certain vector platforms as well as their scopes of application, including an additional section on experimental COVID-19 vaccines.

Reverse genetics of parrot bornavirus 4 reveals a unique splicing of the glycoprotein gene that affects viral propagation

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.

Vaccination against Borna Disease: Overview, Vaccine Virus Characterization and Investigation of Live and Inactivated Vaccines

(1) Background: Vaccination of horses and sheep against Borna disease (BD) was common in endemic areas of Germany in the 20th century but was abandoned in the early 1990s. The recent occurrence of fatal cases of human encephalitis due to Borna disease virus 1 (BoDV-1) has rekindled the interest in vaccination. (2) Methods: The full genomes of the BD live vaccine viruses "Dessau" and "Giessen" were sequenced and analyzed for the first time. All vaccination experiments followed a proof-of-concept approach. Dose-titration infection experiments were performed in rabbits, based on both cell culture- and brain-derived viruses at various doses. Inactivated vaccines against BD were produced from concentrated cell culture supernatants and investigated in rabbits and horses. The BoDV-1 live vaccine "Dessau" was administered to horses and antibody profiles were determined. (3) Results: The BD live vaccine viruses "Dessau" and "Giessen" belong to clusters 3 and 4 of BoDV-1. Whereas the "Giessen" virus does not differ substantially from field viruses, the "Dessau" virus shows striking differences in the M gene and the N-terminal part of the G gene. Rabbits infected with high doses of cell-cultured virus developed neutralizing antibodies and were protected from disease, whereas rabbits infected with low doses of cell-cultured virus, or with brain-derived virus did not. Inactivated vaccines were administered to rabbits and horses, following pre-defined vaccination schemes consisting of three vaccine doses of either adjuvanted or nonadjuvanted inactivated virus. Their immunogenicity and protective efficacy were compared to the BD live vaccine "Dessau". Seventy per cent of horses vaccinated with the BD live vaccine "Dessau" developed neutralizing antibodies after vaccination. (4) Conclusion: Despite a complex evasion of immunological responses by bornaviruses, some vaccination approaches can protect against clinical disease. For optimal effectiveness, vaccines should be administered at high doses, following vaccination schemes consisting of three vaccine doses as basic immunization. Further investigations are necessary in order to investigate and improve protection against infection and to avoid side effects.

Word recognition memory and serum levels of Borna disease virus specific circulating immune complexes in obsessive-compulsive disorder

BACKGROUND

Borna disease virus 1 (BoDV-1) is a non-segmented, negative-strand RNA virus that persistently infects mammals including humans. BoDV-1 worldwide occurring strains display highly conserved genomes with overlapping genetic signatures between those of either human or animal origin. BoDV-1 infection may cause behavioral and cognitive disturbances in animals but has also been found in human major depression and obsessive-compulsive disorder (OCD). However, the impact of BoDV-1 on memory functions in OCD is unknown.

METHOD

To evaluate the cognitive impact of BoDV-1 in OCD, event-related brain potentials (ERPs) were recorded in a continuous word recognition paradigm in OCD patients (n = 16) and in healthy controls (n = 12). According to the presence of BoDV-1-specific circulating immune complexes (CIC), they were divided into two groups, namely group H (high) and L (low), n = 8 each. Typically, ERPs to repeated items are characterized by more positive waveforms beginning approximately 250 ms post-stimulus. This "old/new effect" has been shown to be relevant for memory processing. The early old/new effect (ca. 300-500 ms) with a frontal distribution is proposed to be a neural correlate of familiarity-based recognition. The late old/new effect (post-500 ms) is supposed to reflect memory recollection processes.

RESULTS

OCD patients were reported to show a normal early old/new effect and a reduced late old/new effect compared to normal controls. In our study, OCD patients with a high virus load (group H) displayed exactly these effects, while patients with a low virus load (group L) did not differ from healthy controls.

CONCLUSION

These results confirmed that OCD patients had impaired memory recollection processes compared to the normal controls which may to some extent be related to their BoDV-1 infection.

Nucleoprotein (P40) Binding to 5HT2C Receptors (5HT2CR) is the Key Point in the Pathogenesis of BoDV-1-Infected Hosts

Nucleoprotein (P40) is one of the most important proteins of Borna disease virus 1 (BoDV-1), but which proteins it would bind to in the pathogenesis of BoDV-1-infected hosts is unknown. We used lentivirus LV5-P40 overexpressing P40 to infect primary hippocampal neurons and characterized the interactome of P40 with co-immunoprecipitation (Co-IP) followed by mass spectrometry (MS) analysis. These interacting protein partners revealed the pathogenesis of BoDV-1-infected hosts. We also show for the first time that P40 interacts with 5HT2CR in rat neurons, which may be the molecular basis leading to neuropsychiatric diseases such as anxiety disorders and behavioral abnormalities after BoDV-1 infection of hosts.

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.

BUD23-TRMT112 interacts with the L protein of Borna disease virus and mediates the chromosomal tethering of viral ribonucleoproteins

Persistent intranuclear infection is an uncommon infection strategy among RNA viruses. However, Borna disease virus 1 (BoDV-1), a nonsegmented, negative-strand RNA virus, maintains viral infection in the cell nucleus by forming structured aggregates of viral ribonucleoproteins (vRNPs), and by tethering these vRNPs onto the host chromosomes. To better understand the nuclear infection strategy of BoDV-1, we determined the host protein interactors of the BoDV-1 large (L) protein. By proximity-dependent biotinylation, we identified several nuclear host proteins interacting with BoDV-1 L, one of which is TRMT112, a partner of several RNA methyltransferases (MTase). TRMT112 binds with BoDV-1 L at the RNA-dependent RNA polymerase domain, together with BUD23, an 18S rRNA MTase and 40S ribosomal maturation factor. We then discovered that BUD23-TRMT112 mediates the chromosomal tethering of BoDV-1 vRNPs, and that the MTase activity is necessary in the tethering process. These findings provide us a better understanding on how nuclear host proteins assist the chromosomal tethering of BoDV-1, as well as new prospects of host-viral interactions for intranuclear infection strategy of orthobornaviruses. This article is protected by copyright. All rights reserved.

Full-length genomic sequencing and characterization of Borna disease virus 1 isolates: Lessons in epidemiology

Borna disease virus 1 (BoDV-1) is a nonsegmented, negative-strand RNA virus that infects mammals including humans. BoDV-1 strains occur globally, dominate the species Mammalian 1 bornavirus, and display highly conserved genomes and persistent infection (brain, blood). Subclinical infections prevail but the rare fatal outcomes even in people need awareness and risk assessment. Although BoDV-1 strains were successfully isolated, only limited full genomic sequences are available. In this study, the entire genomes of two natural BoDV-1 isolates (Hu-H2, Equ-Cres) and one vaccine strain (DessVac) were sequenced. They were compared with 20 genomes and 20 single-gene sequences (N and P) of worldwide human strains from psychiatric and neurologic patients and animal strains from horses with Borna disease available at GenBank. Phylogenetic analyses confirmed a low divergence not exceeding 5.55%, 5.34%, and 4.94% at the genome, P-gene, and N-gene level, respectively, characteristic of BoDV-1. Human viruses tended to cluster at the country level but appeared to be independent of hosts' diseases and/or time of isolation. Notably, our data also indicated that human viruses provided individual genetic signatures but exhibited no distinct genotypes that separated them from animal strains. Sequence similarities thus occurred between different host species and distant geographic regions, supporting global BoDV-1 prevalence. Overall low genetic divergence among BoDV-1 viruses shown here also argued against zoonotic concepts, requiring further clarification beyond sequence similarities. Finally, unlike shared sequence conservation, phenotyping of natural and laboratory variants revealed that they manipulated host cells differently, underpinning the authenticity of the human BoDV-1 strains.

Evolutionary Selection of the Nuclear Localization Signal in the Viral Nucleoprotein Leads to Host Adaptation of the Genus Orthobornavirus

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.

Reverse genetics approaches of Borna disease virus: applications in development of viral vectors and preventive vaccines

The plasmid-based reverse genetics system, which involves generation of recombinant viruses from cloned cDNA, has accelerated the understanding of clinical and virological aspects of different viruses. Borna disease virus (BoDV) is a nonsegmented, negative-strand RNA virus that causes persistent intranuclear infection in various vertebrate species. Since its first report, reverse genetics approaches with modified strategies have greatly improved rescue efficiency of recombinant BoDV and enhanced the understanding of function of each viral protein and mechanism of intranuclear persistency. Here, we summarize different reverse genetics approaches of BoDV and recent developments in the use of reverse genetics for generation of viral vectors for gene therapy and virus-like particles for potential preventive vaccines.

Update on immunopathology of bornavirus infections in humans and animals

Knowledge on bornaviruses has expanded tremendously during the last decade through detection of novel bornaviruses and endogenous bornavirus-like elements in many eukaryote genomes, as well as by confirmation of insectivores as reservoir species for classical Borna disease virus 1 (BoDV-1). The most intriguing finding was the demonstration of the zoonotic potential of lethal human bornavirus infections caused by a novel bornavirus of different squirrel species (variegated squirrel 1 bornavirus, VSBV-1) and by BoDV-1 known as the causative agent for the classical Borna disease in horses and sheep. Whereas a T cell-mediated immunopathology has already been confirmed as key disease mechanism for infection with BoDV-1 by experimental studies in rodents, the underlying pathomechanisms remain less clear for human bornavirus infections, infection with other bornaviruses or infection of reservoir species. Thus, an overview of current knowledge on the pathogenesis of bornavirus infections focusing on immunopathology is given.

Antiviral treatment perspective against Borna disease virus 1 infection in major depression: a double-blind placebo-controlled randomized clinical trial

Background

Whether Borna disease virus (BDV-1) is a human pathogen remained controversial until recent encephalitis cases showed BDV-1 infection could even be deadly. This called to mind previous evidence for an infectious contribution of BDV-1 to mental disorders. Pilot open trials suggested that BDV-1 infected depressed patients benefitted from antiviral therapy with a licensed drug (amantadine) which also tested sensitive in vitro. Here, we designed a double-blind placebo-controlled randomized clinical trial (RCT) which cross-linked depression and BDV-1 infection, addressing both the antidepressant and antiviral efficacy of amantadine.

Methods

The interventional phase II RCT (two 7-weeks-treatment periods and a 12-months follow-up) at the Hannover Medical School (MHH), Germany, assigned currently depressed BDV-1 infected patients with either major depression (MD; N = 23) or bipolar disorder (BD; N = 13) to amantadine sulphate (PK-Merz®; twice 100 mg orally daily) or placebo treatment, and contrariwise, respectively. Clinical changes were assessed every 2–3 weeks by the 21-item Hamilton rating scale for depression (HAMD) (total, single, and combined scores). BDV-1 activity was determined accordingly in blood plasma by enzyme immune assays for antigens (PAG), antibodies (AB) and circulating immune complexes (CIC).

Results

Primary outcomes (≥25% HAMD reduction, week 7) were 81.3% amantadine vs. 35.3% placebo responder (p = 0.003), a large clinical effect size (ES; Cohen’s d) of 1.046, and excellent drug tolerance. Amantadine was safe reducing suicidal behaviour in the first 2 weeks. Pre-treatment maximum infection levels were predictive of clinical improvement (AB, p = 0.001; PAG, p = 0.026; HAMD week 7). Respective PAG and CIC levels correlated with AB reduction (p = 0,001 and p = 0.034, respectively). Follow-up benefits (12 months) correlated with dropped cumulative infection measures over time (p < 0.001). In vitro, amantadine concentrations as low as 2.4–10 ng/mL (50% infection-inhibitory dose) prevented infection with human BDV Hu-H1, while closely related memantine failed up to 100,000-fold higher concentration (200 μg/mL).

Conclusions

Our findings indicate profound antidepressant efficacy of safe oral amantadine treatment, paralleling antiviral effects at various infection levels. This not only supports the paradigm of a link of BDV-1 infection and depression. It provides a novel possibly practice-changing low cost mental health care perspective for depressed BDV-1-infected patients addressing global needs.

Trial registration

The trial was retrospectively registered in the German Clinical Trials Registry on 04th of March 2015. The trial ID is DRKS00007649; https://www.drks.de/drks_web/setLocale_EN.do

Zoonotic spillover infections with Borna disease virus 1 leading to fatal human encephalitis, 1999-2019: an epidemiological investigation

BACKGROUND

In 2018-19, Borna disease virus 1 (BoDV-1), the causative agent of Borna disease in horses, sheep, and other domestic mammals, was reported in five human patients with severe to fatal encephalitis in Germany. However, information on case frequencies, clinical courses, and detailed epidemiological analyses are still lacking. We report the occurrence of BoDV-1-associated encephalitis in cases submitted to the Institute of Clinical Microbiology and Hygiene, Regensburg University Hospital, Regensburg, Germany, and provide a detailed description of newly identified cases of BoDV-1-induced encephalitis.

METHODS

All brain tissues from 56 encephalitis cases from Bavaria, Germany, of putative viral origin (1999-2019), which had been submitted for virological testing upon request of the attending clinician and stored for stepwise diagnostic procedure, were systematically screened for BoDV-1 RNA. Two additional BoDV-1-positive cases were contributed by other diagnostic centres. Positive results were confirmed by deep sequencing, antigen detection, and determination of BoDV-1-reactive antibodies in serum and cerebrospinal fluid. Clinical and epidemiological data from infected patients were collected and analysed.

FINDINGS

BoDV-1 RNA and bornavirus-reactive antibodies were detected in eight newly analysed encephalitis cases and the first human BoDV-1 isolate was obtained from an unequivocally confirmed human BoDV-1 infection from the endemic area. Six of the eight BoDV-1-positive patients had no record of immunosuppression before the onset of fatal disease, whereas two were immunocompromised after solid organ transplantation. Typical initial symptoms were headache, fever, and confusion, followed by various neurological signs, deep coma, and severe brainstem involvement. Seven of nine patients with fatal encephalitis of unclear cause were BoDV-1 positive within one diagnostic centre. BoDV-1 sequence information and epidemiological analyses indicated independent spillover transmissions most likely from the local wild animal reservoir.

INTERPRETATION

BoDV-1 infection has to be considered as a potentially lethal zoonosis in endemic regions with reported spillover infections in horses and sheep. BoDV-1 infection can result in fatal encephalitis in immunocompromised and apparently healthy people. Consequently, all severe encephalitis cases of unclear cause should be tested for bornaviruses especially in endemic regions.

FUNDING

German Federal Ministry of Education and Research.

Intranasal Borna Disease Virus (BoDV-1) Infection: Insights into Initial Steps and Potential Contagiosity

Mammalian Bornavirus (BoDV-1) typically causes a fatal neurologic disorder in horses and sheep, and was recently shown to cause fatal encephalitis in humans with and without transplant reception. It has been suggested that BoDV-1 enters the central nervous system (CNS) via the olfactory pathway. However, (I) susceptible cell types that replicate the virus for successful spread, and (II) the role of olfactory ensheathing cells (OECs), remained unclear. To address this, we studied the intranasal infection of adult rats with BoDV-1 in vivo and in vitro, using olfactory mucosal (OM) cell cultures and the cultures of purified OECs. Strikingly, in vitro and in vivo, viral antigen and mRNA were present from four days post infection (dpi) onwards in the olfactory receptor neurons (ORNs), but also in all other cell types of the OM, and constantly in the OECs. In contrast, in vivo, BoDV-1 genomic RNA was only detectable in adult and juvenile ORNs, nerve fibers, and in OECs from 7 dpi on. In vitro, the rate of infection of OECs was significantly higher than that of the OM cells, pointing to a crucial role of OECs for infection via the olfactory pathway. Thus, this study provides important insights into the transmission of neurotropic viral infections with a zoonotic potential.

Genomic characterization, phylogenetic position and in situ localization of a novel putative mononegavirus in Lepeophtheirus salmonis

The complete genome sequence of a novel mononegavirus, Lepeophtheirus salmonis negative-stranded RNA virus 1 (LsNSRV-1), obtained from a salmonid ectoparasite, Lepeophtheirus salmonis was determined. The viral genome contains five open reading frames encoding three unknown proteins (ORF I, II and III), a putative glycoprotein (G), and a large (L) protein. Phylogenetic analysis placed LsNSRV-1 in the recently established mononegaviral family Artoviridae. LsNSRV-1 showed a prevalence of around 97% and was detected in all L. salmonis developmental stages. Viral genomic and antigenomic RNA was localized to nerve tissue, connective tissue, epithelial cells of the gut, subepidermal tissue, exocrine and cement glands, as well as the testis, vas deferens and spermatophore sac of male L. salmonis and the ovaries and oocytes of females. Viral RNA was detected in both the cytoplasm and the nucleoli of infected cells, and putative nuclear export and localization signals were found within the ORF I, III and L proteins, suggesting nuclear replication of LsNSRV-1. RNA interference (RNAi) was induced twice during development by the introduction of a double-stranded RNA fragment of ORF I, resulting in a transient knockdown of viral RNA. A large variation in the knockdown level was seen in adult males and off springs of knockdown animals, whereas the RNA level was more stable in adult females. Together with the localization of viral RNA within the male spermatophore and female oocytes and the amplification of viral RNA in developing embryos, this suggests that LsNSRV-1 is transmitted both maternally and paternally. Small amounts of viral RNA were detected at the site where chalimi were attached to the skin of Atlantic salmon (Salmo salar). However, as the RNAi-mediated treatment did not result in LsNSRV-1-negative offspring and the virus failed to replicate in the tested fish cell cultures, it is difficult to investigate the influence of secreted LsNSRV-1 on the salmon immune response.

Generation of a non-transmissive Borna disease virus vector lacking both matrix and glycoprotein genes

Borna disease virus (BoDV), a prototype of mammalian bornavirus, is a non-segmented, negative strand RNA virus that often causes severe neurological disorders in infected animals, including horses and sheep. Unique among animal RNA viruses, BoDV transcribes and replicates non-cytopathically in the cell nucleus, leading to establishment of long-lasting persistent infection. This striking feature of BoDV indicates its potential as an RNA virus vector system. It has previously been demonstrated by our team that recombinant BoDV (rBoDV) lacking an envelope glycoprotein (G) gene develops persistent infections in transduced cells without loss of the viral genome. In this study, a novel non-transmissive rBoDV, rBoDV ΔMG, which lacks both matrix (M) and G genes in the genome, is reported. rBoDV-ΔMG expressing green fluorescence protein (GFP), rBoDV ΔMG-GFP, was efficiently generated in Vero/MG cells stably expressing both BoDV M and G proteins. Infection with rBoDV ΔMG-GFP was persistently maintained in the parent Vero cells without propagation within cell culture. The optimal ratio of M and G for efficient viral particle production by transient transfection of M and G expression plasmids into cells persistently infected with rBoDV ΔMG-GFP was also demonstrated. These findings indicate that the rBoDV ΔMG-based BoDV vector may provide an extremely safe virus vector system and could be a novel strategy for investigating the function of M and G proteins and the host range of bornaviruses.

Divergent bornaviruses from Australian carpet pythons with neurological disease date the origin of extant Bornaviridae prior to the end-Cretaceous extinction

Tissue samples from Australian carpet pythons (Morelia spilota) with neurological disease were screened for viruses using next-generation sequencing. Coding complete genomes of two bornaviruses were identified with the gene order 3'-N-X-P-G-M-L, representing a transposition of the G and M genes compared to other bornaviruses and most mononegaviruses. Use of these viruses to search available vertebrate genomes enabled recognition of further endogenous bornavirus-like elements (EBLs) in diverse placental mammals, including humans. Codivergence patterns and shared integration sites revealed an ancestral laurasiatherian EBLG integration (77 million years ago [MYA]) and a previously identified afrotherian EBLG integration (83 MYA). The novel python bornaviruses clustered more closely with these EBLs than with other exogenous bornaviruses, suggesting that these viruses diverged from previously known bornaviruses prior to the end-Cretaceous (K-Pg) extinction, 66 MYA. It is possible that EBLs protected mammals from ancient bornaviral disease, providing a selective advantage in the recovery from the K-Pg extinction. A degenerate PCR primer set was developed to detect a highly conserved region of the bornaviral polymerase gene. It was used to detect 15 more genetically distinct bornaviruses from Australian pythons that represent a group that is likely to contain a number of novel species.

Different inhibitory effects on the proliferation and apoptosis of human and laboratory Borna disease virus‑infected human neuroblastoma SH‑SY5Y cells in vitro

Borna disease virus (BDV) is a neurotropic and non‑cytolytic virus, which causes behavioral disorders in a wide range of warm‑blooded species. It is well established that BDV induces neurodegeneration by impairing neurogenesis and interfering with neuronal functioning in the limbic system. In the present study, the potential role of BDV infection in SH‑SY5Y cells was identified, and comparisons of two original BDV strains (the human Hu‑H1 and the laboratory Strain V) were performed to further elucidate the phenotypes of BDV pathogenesis with strain differences. Cell Counting Kit‑8 and flow cytometric analyses revealed that the two BDV strain‑infected groups exhibited marked anti‑proliferation and cell cycle arrest compared with the control group, and the Hu‑H1 strain caused more evident effects. However, the Hu‑H1 strain did not exert effects on the apoptosis of SH‑SH5Y cells, while Strain V led to a marked increase in apoptosis upon initial infection. Western blot analysis confirmed the upregulation of apoptosis regulator BAX protein and the downregulation of apoptosis regulator Bcl‑2 protein caused by the two BDV strains. The results of the present study provided evidence that infection with BDV suppressed SH‑SY5Y cellular functioning and exhibited divergent antiproliferative and apoptotic roles in cells between the two strains. The present study provided an insight for future investigation of strain differences and underlying pathomechanisms.

Linkage between the leader sequence and leader RNA production in Borna disease virus-infected cells

The 3'-untranslated region (UTR) of the non-segmented, negative-strand (NNS) RNA viral genome is called the leader sequence, and functions as the promoter for viral replication and transcription. NNS RNA viruses also use the sequence as a template to synthesize leader RNAs (leRNAs) with unknown functions. Borna disease virus (BDV) is unique because it establishes a persistent infection and replicates in the nucleus. No report has yet demonstrated the presence of leRNAs during BDV infection. Here, we report that BDV synthesizes leRNAs from the 3'-UTR of the genome. They started at position 5 in the 3'-UTR and ended by the transcription start signal of the nucleoprotein gene. The level of leRNA production is not correlated with the levels of viral replication and transcription. On the other hand, mutation of the 3'-UTR affects leRNA production. Our findings add a novel viral transcript to the BDV life cycle and shed light on BDV replication and/or transcription.

Identification and bioinformatic analysis of dysregulated microRNAs in human oligodendroglial cells infected with borna disease virus

MicroRNAs (miRNAs) are recognized as important regulators of gene expression via translational depression or mRNA degradation. Previously, dysregulated miRNAs have been found in neurodegenerative and neuropsychiatric disorders. Borna disease virus (BDV) is a neurotropic, negative single‑stranded RNA virus, which may be a cause of human neuropsychiatric disease. BDV is regarded as an ideal model to analyze the molecular mechanisms of mental disorders caused by viral infection. In the present study, 10 miRNAs were dysregulated in human oligodendrocytes (OL cells) infected with the BDV strain, Hu‑H1 (OL/BDV). The predicted target genes of those different miRNAs were closely associated with DNA binding, receptor activity, cytoplasm and membrane, biopolymer metabolic process and signal transduction, which were ranked highest using Gene Ontology (GO) analysis, and were predominantly involved in 'Immune system and adaptive Immune system pathways' on pathway analysis. Reverse transcription‑quantitative polymerase chain reaction analysis confirmed that seven miRNAs (miR‑1290, miR‑1908, miR‑146a‑5p, miR‑424‑5p, miR‑3676‑3p, miR‑296‑3p and miR‑7‑5p) were significantly downregulated in the OL/BDV cells, whereas two miRNAs (miR‑1244 and miR‑4521) showed no significant differences between the two groups. The present study revealed for the first time, to the best of our knowledge, the miRNA profile of BDV Hu‑H1‑infected human OL cells. Based on GO and pathway analyses, further investigation of the signaling processes in BDV‑infected oligodendrocytes may offer particular promise in improving understanding of the neuropathogenesis of BDV.

The Hydrophobic Mannose Derivative 1B6TM Efficiently Inhibits Borna Disease Virus in Vitro

α-D-Mannnose occupies the terminal position on the N-linked carbohydrate side chain of BDV-specific gp17 (Stoyloff et al., 1994). A hydrophobic derivative of this sugar residue, the 1-0-benzyl-6-0-trityl-α-D-mannnopyranoside (1B6TM), showed a potent and selective inhibition of BDV-replication in vitro, using a range of host-cell/virus systems. When tested in comparison with the unmodified sugar, 1B6TM inhibited the infection in a dose-dependent manner up to 100% without effecting cell viability. After removal of the compound, the antiviral effect remained for several hours. These results suggest that simple modified carbohydrate molecules of BDV-specific sugar residues are able to interfere with virus replication.

Knock-Down of Endogenous Bornavirus-Like Nucleoprotein 1 Inhibits Cell Growth and Induces Apoptosis in Human Oligodendroglia Cells

Endogenous bornavirus-like nucleoprotein elements (EBLNs) have been discovered in the genomes of various animals including humans, whose functions have been seldom studied. To explore the biological functions of human EBLNs, we constructed a lentiviral vector expressing a short-hairpin RNA against human EBLN1, which successfully inhibited EBLN1 expression by above 80% in infected human oligodendroglia cells (OL cells). We found that EBLN1 silencing suppressed cell proliferation, induced G2/M phase arrest, and promoted apoptosis in OL cells. Gene expression profiling demonstrated that 1067 genes were up-regulated, and 2004 were down-regulated after EBLN1 silencing. The top 10 most upregulated genes were PI3, RND3, BLZF1, SOD2, EPGN, SBSN, INSIG1, OSMR, CREB3L2, and MSMO1, and the top 10 most-downregulated genes were KRTAP2-4, FLRT2, DIDO1, FAT4, ESCO2, ZNF804A, SUV420H1, ZC3H4, YAE1D1, and NCOA5. Pathway analysis revealed that these differentially expressed genes were mainly involved in pathways related to the cell cycle, the mitogen-activated protein kinase pathway, p53 signaling, and apoptosis. The gene expression profiles were validated by using quantitative reverse transcription polymerase chain reaction (RT-PCR) for detecting these 20 most-changed genes. Three genes closely related to glioma, RND3, OSMR, and CREB3L2, were significantly upregulated and might be the key factors in EBLN1 regulating the proliferation and apoptosis of OL cells. This study provides evidence that EBLN1 plays a key role in regulating cell life and death, thereby opening several avenues of investigation regarding EBLN1 in the future.

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.

X-linked RNA-binding motif protein (RBMX) is required for the maintenance of Borna disease virus nuclear viral factories

Borna disease virus (BDV) is a non-segmented, negative-strand RNA virus that establishes persistent infection in the nucleus. Although BDV forms viral inclusion bodies, termed viral speckles of transcripts (vSPOTs), which are associated with chromatin in the nucleus, the host factors involved in the maintenance of vSPOTs remain largely unknown. In this study, we identified X-linked RNA-binding motif protein (RBMX) as a nuclear factor interacting with BDV nucleoprotein. Interestingly, knockdown of RBMX led to disruption of the formation of vSPOTs and reduced both transcription and replication of BDV. Our results indicate that RBMX is involved in the maintenance of the structure of the virus factory in the nucleus.

Coding-complete sequencing classifies parrot bornavirus 5 into a novel virus species

In this study, we determined the sequence of the coding region of an avian bornavirus detected in a blue-and-yellow macaw (Ara ararauna) with pathological/histopathological changes characteristic of proventricular dilatation disease. The genomic organization of the macaw bornavirus is similar to that of other bornaviruses, and its nucleotide sequence is nearly identical to the available partial parrot bornavirus 5 (PaBV-5) sequences. Phylogenetic analysis showed that these strains formed a monophyletic group distinct from other mammalian and avian bornaviruses and in calculations performed with matrix protein coding sequences, the PaBV-5 and PaBV-6 genotypes formed a common cluster, suggesting that according to the recently accepted classification system for bornaviruses, these two genotypes may belong to a new species, provisionally named Psittaciform 2 bornavirus.

Borna disease virus infection in cats: ABCD guidelines on prevention and management

OVERVIEW

Borna disease virus (BDV) has a broad host range, affecting primarily horses and sheep, but also cattle, ostriches, cats and dogs. In cats, BDV may cause a non-suppurative meningoencephalomyelitis ('staggering disease').

INFECTION

The mode of transmission is not completely elucidated. Direct and indirect virus transmission is postulated, but BDV is not readily transmitted between cats. Vectors such as ticks may play a role and shrews have been identified as a potential reservoir host. Access to forested areas has been reported to be an important risk factor for staggering disease.

DISEASE SIGNS

It is postulated that BDV may infect nerve endings in the oropharynx and spread via olfactory nerve cells to the central nervous system. A strong T-cell response may contribute to the development of clinical disease. Affected cats develop gait disturbances, ataxia, pain in the lower back and behavioural changes.

DIAGNOSIS

For diagnostic purposes, detection of viral RNA by reverse transcription PCR in samples collected from cats with clinical signs of Borna disease can be considered diagnostic. Serology is of little value; cats without signs of Borna disease may be seropositive and yet not every cat with BDV infection has detectable levels of antibodies.

HUMAN INFECTION

A hypothesis that BDV infection may be involved in the development of selected neurological disorders in man could not be confirmed. A research group within the German Robert Koch Institute studied the potential health threat of BDV to humans and concluded that BDV was not involved in the aetiology of human psychiatric diseases.

Evolution of mammalian and avian bornaviruses

Recently, Avian Bornavirus (ABV) was identified to be a new member of the Bornaviridae family consisting solely of the mammal-infecting Borna disease virus (BDV). Here, to gain more insights into the evolution of these bornaviruses, the time-stamped N gene sequences of BDV genotype 1 (BDV1) and ABV were subjected to Bayesian coalescent analyses. The nucleotide substitution rates and the divergence times were estimated. Age calculations suggested that the first diversification event of the analyzed BDV1 isolates might have taken place about 300years ago, and revealed that ABV was an old virus newly recognized. Great differences were observed in the rate of nucleotide substitution and the pattern of codon usage bias between BDV1 and ABV. Moreover, the analyzed bornaviruses might be descended from an AT-rich ancestor.

The bicolored white-toothed shrew Crocidura leucodon (HERMANN 1780) is an indigenous host of mammalian Borna disease virus

Borna disease (BD) is a sporadic neurologic disease of horses and sheep caused by mammalian Borna disease virus (BDV). Its unique epidemiological features include: limited occurrence in certain endemic regions of central Europe, yearly varying disease peaks, and a seasonal pattern with higher disease frequencies in spring and a disease nadir in autumn. It is most probably not directly transmitted between horses and sheep. All these features led to the assumption that an indigenous virus reservoir of BDV other than horses and sheep may exist. The search for such a reservoir had been unsuccessful until a few years ago five BDV-infected shrews were found in a BD-endemic area in Switzerland. So far, these data lacked further confirmation. We therefore initiated a study in shrews in endemic areas of Germany. Within five years 107 shrews of five different species were collected. BDV infections were identified in 14 individuals of the species bicolored white-toothed shrew (Crocidura leucodon, HERMANN 1780), all originating from BD-endemic territories. Immunohistological analysis showed widespread distribution of BDV antigen both in the nervous system and in epithelial and mesenchymal tissues without pathological alterations. Large amounts of virus, demonstrated by presence of viral antigen in epithelial cells of the oral cavity and in keratinocytes of the skin, may be a source of infection for natural and spill-over hosts. Genetic analyses reflected a close relationship of the BDV sequences obtained from the shrews with the regional BDV cluster. At one location a high percentage of BDV-positive shrews was identified in four consecutive years, which points towards a self-sustaining infection cycle in bicolored white-toothed shrews. Analyses of behavioral and population features of this shrew species revealed that the bicolored white-toothed shrew may indeed play an important role as an indigenous host of BDV.

Evidence for natural Borna disease virus infection in healthy domestic animals in three areas of western China

Borna disease virus (BDV) is a non-cytolytic, neurotropic RNA virus that can infect many vertebrate species, including humans. To date, BDV infection has been reported in a range of animal species across a broad global geographic distribution. However, a systematic epidemiological survey of BDV infection in domesticated animals in China has yet to be performed. In current study, BDV RNA and antibodies in 2353 blood samples from apparently healthy animals of eight species (horse, donkey, dog, pig, rabbit, cattle, goat, sheep) from three areas in western China (Xinjiang province, Chongqing municipality, and Ningxia province) were assayed using reverse transcription qPCR (RT-qPCR) and ELISA assay. Brain tissue samples from a portion of the BDV RNA- and/or antibody-positive animals were subjected to RT-qPCR and western blotting. As a result, varying prevalence of BDV antibodies and/or RNA was demonstrated in various animal species from three areas, ranging from 4.4 % to 20.0 %. Detection of BDV RNA and/or antibodies in Chongqing pigs (9.2 %) provided the first known evidence of BDV infection in this species. Not all brain tissue samples from animals whose blood was BDV RNA and/or antibody positive contained BDV RNA and protein. This study provides evidence that BDV infection among healthy domestic animal species is more widespread in western China than previously believed.

Evidence for Borna disease virus infection in neuropsychiatric patients in three western China provinces

Borna disease virus (BDV) is a non-cytolytic, neurotropic RNA virus that can infect a wide variety of vertebrate species from birds and primates to humans. Several studies have been carried out to investigate whether BDV is associated with neuropsychiatric diseases. However, this association is still inconclusive. Two panels of subjects consisting of 1,679 various neuropsychiatric patients and healthy people from three western China provinces were enrolled in this study. BDV p24 or p40 RNA in peripheral blood mononuclear cells (PBMCs) were detected in the first panel of 1,481 subjects using reverse transcription quantitative polymerase chain reaction (RT-qPCR) and cerebrospinal fluid (CSF) samples from the BDV RNA-positive individuals were subjected to BDV p24 antibodies testing by enzyme-linked immunosorbent assay (ELISA). BDV p24 or p40 RNA in PBMCs and p24 antibodies in plasma were detected in the second panel of 198 subjects by RT-qPCR and Western blot. A higher prevalence for BDV RNA was demonstrated in patients with viral encephalitis (6.70%), Guillain-Barré syndrome (6.70%), schizophrenia (9.90%) and chronic fatigue syndrome (CFS) (12.70%) compared to healthy controls in the first panel. CSF p24 antibodies were demonstrated in three viral encephalitis patients, two schizophrenia patients and two major depressive disorder (MDD) patients. The prevalences of p24 antibodies in plasma from patients with viral encephalitis (13.24%), multiple sclerosis (25.00%) and Parkinson's disease (22.73%) were significantly higher than healthy controls. This study demonstrates that BDV infection also exists in humans from three western China provinces, and suggests the involvement of the contribution of BDV in the aetiology of Chinese patients with some neuropsychiatric disorders, including viral encephalitis, schizophrenia, CFS, multiple sclerosis and Parkinson's disease.

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.

Investigations of cerebrospinal fluid in Borna disease virus seropositive psychiatric patients

Borna disease virus (BDV) appears to cause meningoencephalitis and schizophreniform psychosis in sporadic cases according to earlier cerebrospinal fluid (CSF) inoculation experiments (Rott et al, 1991). However, CSF parameters in BDV seropositive psychiatric patients proved nearly all normal; only the most sensitive CSF/serum index I-BDV for intrathecally produced BDV specific IgG was pathologic in 10.5-29.0% (according to different methodological limits) of patients. An increase in sensitivity was attempted to detect specific IgG in CSF in a part of the cases by concentration. Concentration procedure does not significantly increase methodological bias according to a statistical analysis of the results. Our findings support the hypothesis that BDV may cause or contribute to the pathogenesis of a diagnostically broad pattern of psychiatric syndromes. The occurence of a spectrum of diagnoses is expected from non-specificity of psychiatric symptoms in other infectious diseases of the brain as well as from results in experimental Borna disease (BD) in animals, when a majority of the animals showed rather unspecific symptomatology due to slight, preferentially limbic encephalitis. Slight deficiencies from an earlier BDV infection could explain continuing symptoms in a part of the cases. Recurrences years after infection are well known in experimental and natural BD in animals. It remains open, whether this mechanism could play a more prominent role in a form of "symptomatic" cyclothymia and "symptomatic" schizophrenia, although the results of CSF investigations are more clear in BDV seropositive patients with major psychoses.

[Bornaviruses]

Bornaviridae is an enveloped animal virus carrying an 8.9 kb non-segmented, negative-strand RNA genome. The genus bornavirus contains two members infecting vertebrates, Borna disease virus (BDV) and avian bornavirus (ABV), which could preferably infect the nervous systems. BDV causes classical Borna disease, a progressive meningoencephalomyelitis, in horses and sheep, and ABV is known to induce proventricular dilatation disease, a fatal disease characterized by a lymphocytic, plasmacytic inflammation of central and peripheral nervous tissues, in multiple avian species. Recent evidences have demonstrated that bornavirus is unique among RNA viruses as they not only establish a long-lasting, persistent infection in the nucleus, but also integrate their own DNA genome copy into the host chromosome. In this review, I outline the recent knowledge about the unique virological characteristics of bornaviruses, as well as the diseases caused by the infection of BDV and ABV.

A novel borna disease virus vector system that stably expresses foreign proteins from an intercistronic noncoding region

Borna disease virus (BDV), a nonsegmented, negative-strand RNA virus, infects a wide variety of mammalian species and readily establishes a long-lasting, persistent infection in brain cells. Therefore, this virus could be a promising candidate as a novel RNA virus vector enabling stable gene expression in the central nervous system (CNS). Previous studies demonstrated that the 5' untranslated region of the genome is the only site for insertion and expression of a foreign gene. In this study, we established a novel BDV vector in which an additional transcription cassette has been inserted into an intercistronic noncoding region between the viral phosphoprotein (P) and matrix (M) genes. The recombinant BDV (rBDV) carrying green fluorescent protein (GFP) between the P and M genes, rBDV P/M-GFP, expressed GFP efficiently in cultured cells and rodent brains for a long period of time without attenuation. Furthermore, we generated a nonpropagating rBDV, ΔGLLP/M, which lacks the envelope glycoprotein (G) and a splicing intron within the polymerase gene (L), by the transcomplementation system with either transient or stable expression of the G gene. Interestingly, rBDV ΔGLLP/M established a persistent infection in cultured cells with stable expression of GFP in the absence of the expression of G. Using persistently infected rBDV ΔGLLP/M-infected cells, we determined the amino acid region in the cytoplasmic tail (CT) of BDV G important for the release of infectious rBDV particles and also demonstrated that the CT region may be critical for the generation of pseudotyped rBDV having vesicular stomatitis virus G protein. Our results revealed that the newly established BDV vector constitutes an alternative tool not only for stable expression of foreign genes in the CNS but also for understanding the mechanism of the release of enveloped virions.

Detection and characterization of a distinct bornavirus lineage from healthy Canada geese (Branta canadensis)

Avian bornaviruses (ABV), identified in 2008, infect captive parrots and macaws worldwide. The natural reservoirs of these viruses are unknown. Reverse transcription-PCR (RT-PCR) was used to screen oropharyngeal/cloacal swab and brain samples from wild Canada geese (Branta canadensis) for ABV. Approximately 2.9% of swab samples were positive for bornavirus sequences. Fifty-two percent of brain samples from 2 urban flocks also tested positive, and brain isolates were cultured in duck embryo fibroblasts. Phylogenetic analyses placed goose isolates in an independent cluster, and more notably, important regulatory sequences present in Borna disease virus but lacking in psittacine ABVs were present in goose isolates.

Intracerebral Borna disease virus infection of bank voles leading to peripheral spread and reverse transcription of viral RNA

Bornaviruses, which chronically infect many species, can cause severe neurological diseases in some animal species; their association with human neuropsychiatric disorders is, however, debatable. The epidemiology of Borna disease virus (BDV), as for other members of the family Bornaviridae, is largely unknown, although evidence exists for a reservoir in small mammals, for example bank voles (Myodes glareolus). In addition to the current exogenous infections and despite the fact that bornaviruses have an RNA genome, bornavirus sequences integrated into the genomes of several vertebrates millions of years ago. Our hypothesis is that the bank vole, a common wild rodent species in traditional BDV-endemic areas, can serve as a viral host; we therefore explored whether this species can be infected with BDV, and if so, how the virus spreads and whether viral RNA is transcribed into DNA in vivo.We infected neonate bank voles intracerebrally with BDV and euthanized them 2 to 8 weeks post-infection. Specific Ig antibodies were detectable in 41%. Histological evaluation revealed no significant pathological alterations, but BDV RNA and antigen were detectable in all infected brains. Immunohistology demonstrated centrifugal spread throughout the nervous tissue, because viral antigen was widespread in peripheral nerves and ganglia, including the mediastinum, esophagus, and urinary bladder. This was associated with viral shedding in feces, of which 54% were BDV RNA-positive, and urine at 17%. BDV nucleocapsid gene DNA occurred in 66% of the infected voles, and, surprisingly, occasionally also phosphoprotein DNA. Thus, intracerebral BDV infection of bank vole led to systemic infection of the nervous tissue and viral excretion, as well as frequent reverse transcription of the BDV genome, enabling genomic integration. This first experimental bornavirus infection in wild mammals confirms the recent findings regarding bornavirus DNA, and suggests that bank voles are capable of bornavirus transmission.

Discovery and initial analysis of novel viral genomes in the soybean cyst nematode

Nematodes are the most abundant multicellular animals on earth, yet little is known about their natural viral pathogens. To date, only two nematode virus genomes have been reported. Consequently, nematode viruses have been overlooked as important biotic factors in the study of nematode ecology. Here, we show that one plant parasitic nematode species, Heterodera glycines, the soybean cyst nematode (SCN), harbours four different RNA viruses. The nematode virus genomes were discovered in the SCN transcriptome after high-throughput sequencing and assembly. All four viruses have negative-sense RNA genomes, and are distantly related to nyaviruses and bornaviruses, rhabdoviruses, bunyaviruses and tenuiviruses. Some members of these families replicate in and are vectored by insects, and can cause significant diseases in animals and plants. The novel viral sequences were detected in both eggs and the second juvenile stage of SCN, suggesting that these viruses are transmitted vertically. While there was no evidence of integration of viral sequences into the nematode genome, we indeed detected transcripts from these viruses by using quantitative PCR. These data are the first finding of virus genomes in parasitic nematodes. This discovery highlights the need for further exploration for nematode viruses in all tropic groups of these diverse and abundant animals, to determine how the presence of these viruses affects the fitness of the nematode, strategies of viral transmission and mechanisms of viral pathogenesis.

Genomic RNAs of Borna disease virus are elongated on internal template motifs after realignment of the 3' termini

The terminal structures of the Borna disease virus (BDV) genome (vRNA) and antigenome (cRNA) differ from those of other negative strand RNA viruses, as both molecules possess four nucleotides at the 3' terminus without an apparent template at the 5' end of the opposite strand. Consequently, the v- and cRNA molecules are not perfect mirror images, a situation that is not compatible with conventional strategies to maintain genetic information. We show here that recombinant viruses recovered from cDNA lacking the nontemplated nucleotides efficiently reconstitute the 3' overhangs. Analyses of recombinant viruses encoding genetic markers in potential alternative template sequences demonstrated that the BDV v- and cRNA molecules are extended by a realign-and-elongation process on internal template motifs located in close proximity to the 3' ends of v- and cRNA, respectively. The data further suggest that cRNA elongation is restricted to a single template motif of the nascent strand, whereas elongation of vRNA might use multiple template motifs. We propose that the elongation of the 3' termini supports the terminal integrity of the genomic RNA molecules during BDV persistence, and furthermore provides an elegant strategy to eliminate the triphosphate groups from the 5' termini of the BDV v- and cRNA without compromising the genetic information of the virus.

Expression of interferon gamma in the brain of cats with natural Borna disease virus infection

Borna disease virus (BDV) is a neurotropic, negative-stranded RNA virus, which causes a non-suppurative meningoencephalomyelitis in a wide range of animals. In cats, BDV infection leads to staggering disease. In spite of a vigorous immune response the virus persists in the central nervous system (CNS) in both experimentally and naturally infected animals. Since the CNS is vulnerable to cytotoxic effects mediated via NK-cells and cytotoxic T-cells, other non-cytolytic mechanisms such as the interferon (IFN) system is favourable for viral clearance. In this study, IFN-γ expression in the brain of cats with clinical signs of staggering disease (N=12) was compared to the expression in cats with no signs of this disease (N=7) by quantitative RT-PCR. The IFN-γ expression was normalised against the expression of three reference genes (HPRT, RPS7, YWHAZ). Cats with staggering disease had significantly higher expression of IFN-γ compared to the control cats (p-value ≤ 0.001). There was no significant difference of the IFN-γ expression in BDV-positive (N=7) and -negative (N=5) cats having clinical signs of staggering disease. However, as BDV-RNA still could be detected, despite an intense IFN-γ expression, BDV needs to have mechanisms to evade this antiviral immune response of the host, to be able to persist.

Functional analysis of proteins and protein species using shotgun proteomics and linear mathematics

Covalent post-translational modification of proteins is the primary modulator of protein function in the cell. It greatly expands the functional potential of the proteome compared to the genome. In the past few years shotgun proteomics-based research, where the proteome is digested into peptides prior to mass spectrometric analysis has been prolific in this area. It has determined the kinetics of tens of thousands of sites of covalent modification on an equally large number of proteins under various biological conditions and uncovered a transiently active regulatory network that extends into diverse branches of cellular physiology. In this review, we discuss this work in light of the concept of protein speciation, which emphasizes the entire post-translationally modified molecule and its interactions and not just the modification site as the functional entity. Sometimes, particularly when considering complex multisite modification, all of the modified molecular species involved in the investigated condition, the protein species must be completely resolved for full understanding. We present a mathematical technique that delivers a good approximation for shotgun proteomics data.

Modulation of miR-122 on persistently Borna disease virus infected human oligodendroglial cells

Using RNAhybrid software we found the predicted binding of complementary sequences between miR-122 and viral mRNAs, may be important for the antiviral effect of miR-122 on Borna disease virus (BDV). A moderate expression of miR-122 was identified in human oligodendroglial cells (OL), but with a much lower level of miR-122 in BDV persistent infection (OL/BDV) and cells transfected with BDV gene expression vectors. Over-expression of miR-122 and specific blocking experiments demonstrated that miR-122 was able to specifically inhibit BDV protein synthesis, viral gene replication and transcription, and induce the secretion/synthesis of interferon (IFN) in OL and OL/BDV cells. The abolishment of miR-122 by AMO-122 inhibited endogenous IFN induction by IFN-beta. These results indicate that miR-122 can exert direct antiviral function by inhibiting BDV translation and replication on one hand, while acting indirectly through IFN to increase the host innate immunity to modulate the virus-host interactions on the other hand.

Autogenous translational regulation of the Borna disease virus negative control factor X from polycistronic mRNA using host RNA helicases

Borna disease virus (BDV) is a nonsegmented, negative-strand RNA virus that employs several unique strategies for gene expression. The shortest transcript of BDV, X/P mRNA, encodes at least three open reading frames (ORFs): upstream ORF (uORF), X, and P in the 5′ to 3′ direction. The X is a negative regulator of viral polymerase activity, while the P phosphoprotein is a necessary cofactor of the polymerase complex, suggesting that the translation of X is controlled rigorously, depending on viral replication. However, the translation mechanism used by the X/P polycistronic mRNA has not been determined in detail. Here we demonstrate that the X/P mRNA autogenously regulates the translation of X via interaction with host factors. Transient transfection of cDNA clones corresponding to the X/P mRNA revealed that the X ORF is translated predominantly by uORF-termination-coupled reinitiation, the efficiency of which is upregulated by expression of P. We found that P may enhance ribosomal reinitiation at the X ORF by inhibition of the interaction of the DEAD-box RNA helicase DDX21 with the 5′ untranslated region of X/P mRNA, via interference with its phosphorylation. Our results not only demonstrate a unique translational control of viral regulatory protein, but also elucidate a previously unknown mechanism of regulation of polycistronic mRNA translation using RNA helicases.

All viruses rely on host cell factors to complete their life cycles. Therefore, the replication strategies of viruses may provide not only the understanding of virus pathogenesis but also useful models to disentangle the complex machinery of host cells. Translation regulation of viral mRNA is a good example of this. Borna disease virus (BDV) is a highly neurotropic RNA virus which is characterized by persistent infection. BDV expresses mRNAs as polycistronic coding transcripts. Among them, the 0.8 kb X/P mRNA encodes at least three open reading frames (ORFs), upstream ORF, X, and P. Although BDV X and P have opposing effects in terms of viral polymerase activity, the translational regulation of X/P polycistronic mRNA has not been elucidated. In this study, we show an ingenious strategy of translational control of viral regulatory protein using host factors. We demonstrate that host RNA helicases, mainly DDX21, can affect ribosomal reinitiation of X via interaction with the 5′ untranslated region (UTR) of X/P mRNA and that the downstream P protein autogenously controls the translation of X by interfering with the binding of DDX21 to the 5′ UTR. Our findings uncover not only a unique translational control of viral regulatory protein but also a previously unknown mechanism of translational regulation of polycistronic mRNA using RNA helicases.

Detection and analysis of Borna disease virus in Chinese patients with neurological disorders

BACKGROUND AND PURPOSE

Borna disease virus (BDV) is a neurotropic RNA virus that is known to cause neurological disturbances in various animal species, potentially even humans. However, the association between BDV infection and human neurological disorders remains unclear.

METHODS

Between August 2005 and March 2006, 65 patients with neurological disorders were enrolled into our study. The presence of BDV p24 RNA from peripheral blood mononuclear cells (PBMCs) was investigated by using nested reverse transcriptase PCR (RT-PCR) assay.

RESULTS

Borna disease virus p24 RNA was detected from PBMCs in six patients with viral encephalitis by using nested RT-PCR assay. However, BDV p24 RNA was not detected in patients with multiple sclerosis or peripheral nerve diseases.

CONCLUSION

There might be possible associations between BDV infection and human viral encephalitis.

Binding properties of GP1 protein of Borna disease virus

The surface glycoprotein (G) of Borna disease virus (BDV) plays central roles in the process of viral entry. BDV G is cleaved by cellular furin-like proteases into two components, GP1 and GP2. Although GP1 is involved in the virus entry into cells, the binding activity of GP1 to cells is unknown. Therefore, we expressed the wild-type GP1 and a variety of GP1 deletion mutants that were FLAG-tagged at the C-terminus in human embryonic kidney 293T cells. These proteins were then purified using an anti-FLAG antibody and evaluated for their ability to bind to cell lines. GP1 bound to BDV-permissive cells but not to non-permissive cells. GP1 also inhibited BDV infection via its binding to cells. This binding assay should prove useful to map the receptor-binding domain of BDV.

Identification of RNA instability elements in Borna disease virus

Genome organization and gene expression of Borna disease virus (BDV) are remarkable for the overlap of open reading frames, transcription units and transcription signals, readthrough of transcription termination signals, differential use of translation initiation codons, and exploitation of the cellular splicing machinery. Here we report an additional control of gene expression at the level of mRNA stability. Levels of BDV proteins in infected cells do not correspond to the transcriptional gradient typically observed in nonsegmented negative-sense RNA viruses. The third transcription unit of BDV's negative-sense RNA genome encodes viral proteins M, G and L. Analysis of the third transcription unit identified RNA-destabilizing domains with the most pronounced activity located in regions spanning nucleotides 2818-2918 (instability domain-1) and 4022-4071 (instability domain-2). Given that one domain maps to intron-2 and is thereby eliminated upon splicing, this represents an intriguing mechanism for regulating transcript levels independent of a transcriptional gradient. The presence of instability domains in introns offers a mechanism to create the observed discontinuous gradient M>L>G, compatible with the non-cytopathic, persistent infection that is characteristic for BDV, and provides a rationale for the use of alternative splicing by this unusual virus.

Polymerase read-through at the first transcription termination site contributes to regulation of borna disease virus gene expression

An unusually long noncoding sequence is located between the N gene of Borna disease virus (BDV) and the genes for regulatory factor X and polymerase cofactor P. Most of these nucleotides are transcribed and seem to control translation of the bicistronic X/P mRNA. We report here that Vero cells persistently infected with mutant viruses containing minor alterations in this control region showed almost normal levels of N, X, and P proteins but exhibited greatly reduced levels of mRNAs coding for these viral gene products. Surprisingly, cells infected with these BDV mutants accumulated a viral transcript 1.9 kb in length that represents a capped and polyadenylated mRNA containing the coding regions of the N, X, and P genes. Cells infected with wild-type BDV also contained substantial amounts of this read-through mRNA, which yielded both N and P protein when translated in vitro. Viruses carrying mutations that promoted read-through transcription at the first gene junction failed to replicate in the brain of adult rats. In the brains of newborn rats, these mutant viruses were able to replicate after acquiring second-site mutations in or near the termination signal located downstream of the N gene. Thus, sequence elements adjacent to the core termination signal seem to regulate the frequency by which the polymerase terminates transcription after the N gene. We conclude from these observations that BDV uses read-through transcription for fine-tuning the expression of the N, X, and P genes which, in turn, influence viral polymerase activity.