Differential transcription attenuation of rabies virus genes by intergenic regions: generation of recombinant viruses overexpressing the polymerase gene

Evolution and divergence of the genetic lineage Desmodus rotundus/Artibeus lituratus of rabies virus in São Paulo State

The last record of a rabies case caused by the dog-specific rabies virus (RABV) lineage in dogs or cats in São Paulo State was in 1998. From 2002 to 2021, 57 cases of rabies in these animals were reported, and the vast majority (51) were genetically characterized as belonging to the Desmodus rotundus/Artibeus lituratus RABV lineage. However, it is not currently possible to infer which of these bats is the source of infection by genome sequencing of RABV isolates. The aims of this study were (a) to characterize the Desmodus rotundus/Artibeus lituratus lineage to determine the relationships between the RABV lineages and each reservoir, (b) to assess the phylogeny and common ancestors of the RABV lineages found in D. rotundus and A. lituratus, and (c) to further understand the epidemiology and control of rabies. In this study, we genetically analyzed 70 RABV isolates from São Paulo State that were received by the Virology Laboratory of the Pasteur Institute of São Paulo between 2006 and 2015. Of these isolates, 33 were associated with the hematophagous bat D. rotundus and 37 with the fruit bat A. lituratus. A genomic approach using phylogenetic analysis and nucleotide sequence comparisons demonstrated that these isolates belonged to the same genetic lineage of RABV. We also found that, in São Paulo State, the D. rotundus/A. lituratus lineage could be subdivided into at least four phylogenetic sublineages: two associated with D. rotundus and two with A. lituratus. These results are of importance for the epidemiological surveillance of rabies in São Paulo.

Characterisation of a Live-Attenuated Rabies Virus Expressing a Secreted scFv for the Treatment of Rabies

Rabies virus (RABV) causes possibly the oldest disease and is responsible for an estimated >59,000 human fatalities/year. Post exposure prophylaxis (PEP), the administration of vaccine and rabies immunoglobulin, is a highly effective tool which is frequently unavailable in RABV endemic areas. Furthermore, due to the constraints of the blood-brain barrier, current PEP regimes are ineffective after the onset of clinical symptoms which invariably result in death. To circumvent this barrier, a live-attenuated recombinant RABV expressing a highly RABV-neutralising scFv antibody (62-71-3) linked to the fluorescent marker mCherry was designed. Once rescued, the resulting construct (named RABV-62scFv) was grown to high titres, its growth and cellular dissemination kinetics characterised, and the functionality of the recombinant 62-71-3 scFv assessed. Encouraging scFv production and subsequent virus neutralisation results demonstrate the potential for development of a therapeutic live-attenuated virus-based post-infection treatment (PIT) for RABV infection.

Lyssaviruses and the Fatal Encephalitic Disease Rabies

Lyssaviruses cause the disease rabies, which is a fatal encephalitic disease resulting in approximately 59,000 human deaths annually. The prototype species, rabies lyssavirus, is the most prevalent of all lyssaviruses and poses the greatest public health threat. In Africa, six confirmed and one putative species of lyssavirus have been identified. Rabies lyssavirus remains endemic throughout mainland Africa, where the domestic dog is the primary reservoir - resulting in the highest per capita death rate from rabies globally. Rabies is typically transmitted through the injection of virus-laden saliva through a bite or scratch from an infected animal. Due to the inhibition of specific immune responses by multifunctional viral proteins, the virus usually replicates at low levels in the muscle tissue and subsequently enters the peripheral nervous system at the neuromuscular junction. Pathogenic rabies lyssavirus strains inhibit innate immune signaling and induce cellular apoptosis as the virus progresses to the central nervous system and brain using viral protein facilitated retrograde axonal transport. Rabies manifests in two different forms - the encephalitic and the paralytic form - with differing clinical manifestations and survival times. Disease symptoms are thought to be due mitochondrial dysfunction, rather than neuronal apoptosis. While much is known about rabies, there remain many gaps in knowledge about the neuropathology of the disease. It should be emphasized however, that rabies is vaccine preventable and dog-mediated human rabies has been eliminated in various countries. The global elimination of dog-mediated human rabies in the foreseeable future is therefore an entirely feasible goal.

Rabies Prophylactic and Treatment Options: An In Vitro Study of siRNA- and Aptamer-Based Therapeutics

If the goal of eliminating dog-mediated human rabies by 2030 is to be achieved, effective mass dog vaccination needs to be complemented by effective prophylaxis for individuals exposed to rabies. Aptamers and short-interfering RNAs (siRNAs) have been successful in therapeutics, but few studies have investigated their potential as rabies therapeutics. In this study, siRNAs and aptamers-using a novel selection method-were developed and tested against rabies virus (RABV) in a post-infection (p.i.) scenario. Multiple means of delivery were tested for siRNAs, including the use of Lipofectamine and conjugation with the developed aptamers. One siRNA (N53) resulted in an 80.13% reduction in viral RNA, while aptamer UPRET 2.03 demonstrated a 61.3% reduction when used alone at 2 h p.i. At 24 h p.i., chimera UPRET 2.03-N8 (aptamer-siRNA) resulted in a 36.5% inhibition of viral replication. To our knowledge, this is the first study using siRNAs or aptamers that (1) demonstrated significant inhibition of RABV using an aptamer, (2) tested Lipofectamine RNAi-Max as a means for delivery, and (3) produced significant RABV inhibition at 24 h p.i. This study serves as a proof-of-concept to potentially use aptamers and siRNAs as rabies immunoglobulin (RIG) replacements or therapeutic options for RABV and provides strong evidence towards their further investigation.

Transcriptional Control and mRNA Capping by the GDP Polyribonucleotidyltransferase Domain of the Rabies Virus Large Protein

Rabies virus (RABV) is a causative agent of a fatal neurological disease in humans and animals. The large (L) protein of RABV is a multifunctional RNA-dependent RNA polymerase, which is one of the most attractive targets for developing antiviral agents. A remarkable homology of the RABV L protein to a counterpart in vesicular stomatitis virus, a well-characterized rhabdovirus, suggests that it catalyzes mRNA processing reactions, such as 5'-capping, cap methylation, and 3'-polyadenylation, in addition to RNA synthesis. Recent breakthroughs in developing in vitro RNA synthesis and capping systems with a recombinant form of the RABV L protein have led to significant progress in our understanding of the molecular mechanisms of RABV RNA biogenesis. This review summarizes functions of RABV replication proteins in transcription and replication, and highlights new insights into roles of an unconventional mRNA capping enzyme, namely GDP polyribonucleotidyltransferase, domain of the RABV L protein in mRNA capping and transcription initiation.

A new recombinant rabies virus expressing a green fluorescent protein: A novel and fast approach to quantify virus neutralizing antibodies

The Rapid Fluorescent Focus Inhibition Test (RFFIT) is a standard assay used to detect and assess the titers of rabies virus neutralizing antibodies (RVNA) in blood sera. To simplify the multistep RFFIT procedure by eliminating the immunostaining step, we generated a new recombinant RV expressing a green fluorescent protein (rRV-GFP) and assess its suitability for quantifying RVNA. We rescued the rRV-GFP virus from plasmid DNA carrying a full-length genome of the CVS-N2c strain of RV in which the eGFP gene was inserted between the glycoprotein and RNA-polymerase genes. The recombinant virus was genetically stable and grew efficiently in appropriate cells expressing sufficient GFP fluorescence to detect directly 20 h post infection (hpi). We evaluated the feasibility of using rRV-GFP in RFFIT by comparing RVNA titers in 27 serum samples measured by conventional RFFIT and RFFIT-GFP. A linear regression analysis of the data demonstrated a good agreement between these two methods (r = 0.9776) including results with samples having RVNA titers close to the minimally acceptable vaccine potency threshold (0.5 IU/ml). Study results showed that the rRV-GFP virus could replace the CVS-11 challenge virus currently used in the conventional RFFIT and enabling more rapid, simpler, and less expensive detection and quantitation of RVNA.

Plant Viruses in Plant Molecular Pharming: Toward the Use of Enveloped Viruses

Plant molecular pharming has emerged as a reliable platform for recombinant protein expression providing a safe and low-cost alternative to bacterial and mammalian cells-based systems. Simultaneously, plant viruses have evolved from pathogens to molecular tools for recombinant protein expression, chimaeric viral vaccine production, and lately, as nanoagents for drug delivery. This review summarizes the genesis of viral vectors and agroinfection, the development of non-enveloped viruses for various biotechnological applications, and the on-going research on enveloped plant viruses.

Experimental screening studies on rabies virus transmission and oral rabies vaccination of the Greater Kudu (Tragelaphus strepsiceros)

Rabies in the Greater Kudu (Tragelaphus strepsiceros) in Namibia is unique and found in such magnitude as has not been reported elsewhere in southern Africa. Reasons as to why Kudus appear to be exceptionally susceptible to rabies still remain speculative at best. Because the current severe rabies endemic in Kudus continues to have an enormous negative impact on the Namibian agricultural sector, we set out to question existing dogmas regarding the epidemiology of the disease in a unique experimental setting. In addition, we explored effective measures to protect these antelopes. Although we were able to confirm high susceptibly of kudus for rabies and sporadic horizontal rabies virus transmission to contact animals, we contend that these observations cannot plausibly explain the rapid spread of the disease in Kudus over large territories. Since parenteral vaccination of free-roaming Kudus is virtually impossible, oral rabies vaccination using modified life virus vaccines with a high safety profile would be the ultimate solution to the problem. In a proof-of-concept study using a 3rd generation oral rabies virus vaccine construct (SPBN GASGAS) we found evidence that Kudus can be vaccinated by the oral route and protected against a subsequent rabies infection. In a second phase, more targeted studies need to be initiated by focusing on optimizing oral vaccine uptake and delivery.

Nontoxic, double-deletion-mutant rabies viral vectors for retrograde targeting of projection neurons

Recombinant rabies viral vectors have proven useful for applications including retrograde targeting of projection neurons and monosynaptic tracing, but their cytotoxicity has limited their use to short-term experiments. Here we introduce a new class of double-deletion-mutant rabies viral vectors that left transduced cells alive and healthy indefinitely. Deletion of the viral polymerase gene abolished cytotoxicity and reduced transgene expression to trace levels but left vectors still able to retrogradely infect projection neurons and express recombinases, allowing downstream expression of other transgene products such as fluorophores and calcium indicators. The morphology of retrogradely targeted cells appeared unperturbed at 1 year postinjection. Whole-cell patch-clamp recordings showed no physiological abnormalities at 8 weeks. Longitudinal two-photon structural and functional imaging in vivo, tracking thousands of individual neurons for up to 4 months, showed that transduced neurons did not die but retained stable visual response properties even at the longest time points imaged.

Sequencing and sequence analysis of partial nucleoprotein (N) gene and phylogenetic analysis of rabies virus field isolates from Gujarat state, India

The present study was undertaken with an aim of characterization of rabies virus (genus Lyssavirus of the family Rhabdoviridae under the order Mononegavirales) by sequencing of partial nucleoprotein (N) gene of rabies virus and phylogenetic analysis to know the genotype and lineage of rabies virus present in Gujarat state of India. A total of 32 samples (18 brain samples and 14 saliva samples) were aseptically collected from live and dead animals (viz. dog, buffalo, cow, goat, donkey and hyena) for rabies virus detection. Out of 32 samples, 24 samples were found positive by Reverse Transcriptase Polymerase Chain Reactions and from these 24 positive samples, 20 samples were selected for sequencing having good concentration of gene product. ClustalW alignment of nucleotide sequences and amino acid sequences of field rabies isolates revealed 95.20-100 and 97.95-100% similarity among themselves, respectively. Multiple sequence alignment of field rabies isolates and reference vaccine strains [Pasteur strain and Challenge Virus Strain (CVS)] indicated single nucleotide mutations at total 91 positions and amino acid mutations at total 17 different positions. Phylogenetic analysis of N gene sequences using our 20 field rabies isolates and 21 other reported isolates in Genbank resulted in 3 phylogenetic clusters. All the field rabies isolates showed same genetic lineage among themselves and with other earlier reported Indian rabies isolates placing them in Arctic like lineage of Genotype 1 Rabies virus. However, they were at genetic distance with reference Pasteur and CVS strains, which grouped in different phylogenetic cluster.

Rabies - epidemiology, pathogenesis, public health concerns and advances in diagnosis and control: a comprehensive review

Rabies is a zoonotic, fatal and progressive neurological infection caused by rabies virus of the genus Lyssavirus and family Rhabdoviridae. It affects all warm-blooded animals and the disease is prevalent throughout the world and endemic in many countries except in Islands like Australia and Antarctica. Over 60,000 peoples die every year due to rabies, while approximately 15 million people receive rabies post-exposure prophylaxis (PEP) annually. Bite of rabid animals and saliva of infected host are mainly responsible for transmission and wildlife like raccoons, skunks, bats and foxes are main reservoirs for rabies. The incubation period is highly variable from 2 weeks to 6 years (avg. 2-3 months). Though severe neurologic signs and fatal outcome, neuropathological lesions are relatively mild. Rabies virus exploits various mechanisms to evade the host immune responses. Being a major zoonosis, precise and rapid diagnosis is important for early treatment and effective prevention and control measures. Traditional rapid Seller's staining and histopathological methods are still in use for diagnosis of rabies. Direct immunofluoroscent test (dFAT) is gold standard test and most commonly recommended for diagnosis of rabies in fresh brain tissues of dogs by both OIE and WHO. Mouse inoculation test (MIT) and polymerase chain reaction (PCR) are superior and used for routine diagnosis. Vaccination with live attenuated or inactivated viruses, DNA and recombinant vaccines can be done in endemic areas. This review describes in detail about epidemiology, transmission, pathogenesis, advances in diagnosis, vaccination and therapeutic approaches along with appropriate prevention and control strategies.

Rabies

Rabies is a life-threatening neglected tropical disease: tens of thousands of cases are reported annually in endemic countries (mainly in Africa and Asia), although the actual numbers are most likely underestimated. Rabies is a zoonotic disease that is caused by infection with viruses of the Lyssavirus genus, which are transmitted via the saliva of an infected animal. Dogs are the most important reservoir for rabies viruses, and dog bites account for >99% of human cases. The virus first infects peripheral motor neurons, and symptoms occur after the virus reaches the central nervous system. Once clinical disease develops, it is almost certainly fatal. Primary prevention involves dog vaccination campaigns to reduce the virus reservoir. If exposure occurs, timely post-exposure prophylaxis can prevent the progression to clinical disease and involves appropriate wound care, the administration of rabies immunoglobulin and vaccination. A multifaceted approach for human rabies eradication that involves government support, disease awareness, vaccination of at-risk human populations and, most importantly, dog rabies control is necessary to achieve the WHO goal of reducing the number of cases of dog-mediated human rabies to zero by 2030.

Increased transgene expression level of rabies virus vector for transsynaptic tracing

Viral vectors that can infect neurons transsynaptically and can strongly express foreign genes are useful for investigating the organization of neural circuits. We previously developed a propagation-competent rabies virus (RV) vector based on a highly attenuated HEP-Flury strain (rHEP5.0-CVSG), which selectively infects neurons and propagates between synaptically connected neurons in a retrograde direction. Its relatively low level of transgene expression, however, makes immunostaining necessary to visualize the morphological features of infected neurons. To increase the transgene expression level of this RV vector, in this study we focused on two viral proteins: the large protein (L) and matrix protein (M). We first attempted to enhance the expression of L, which is a viral RNA polymerase, by deleting the extra transcription unit and shortening the intergenic region between the G and L genes. This viral vector (rHEP5.0-GctL) showed increased transgene expression level with efficient transsynaptic transport. We next constructed an RV vector with a rearranged gene order (rHEP5.0-GML) with the aim to suppress the expression of M, which plays a regulatory role in virus RNA synthesis. Although this vector showed high transgene expression level, the efficiency of transsynaptic transport was low. To further evaluate the usability of rHEP5.0-GctL as a transsynaptic tracer, we inserted a fluorescent timer as a transgene, which changes the color of its fluorescence from blue to red over time. This viral vector enabled us the differentiation of primary infected neurons from secondary infected neurons in terms of the fluorescence wavelength. We expect this propagation-competent RV vector to be useful for elucidating the complex organization of the central nervous system.

The structurally disordered paramyxovirus nucleocapsid protein tail domain is a regulator of the mRNA transcription gradient

The paramyxovirus RNA-dependent RNA-polymerase (RdRp) complex loads onto the nucleocapsid protein (N)-encapsidated viral N:RNA genome for RNA synthesis. Binding of the RdRp of measles virus (MeV), a paramyxovirus archetype, is mediated through interaction with a molecular recognition element (MoRE) located near the end of the carboxyl-terminal Ntail domain. The structurally disordered central Ntail section is thought to add positional flexibility to MoRE, but the functional importance of this Ntail region for RNA polymerization is unclear. To address this question, we dissected functional elements of Ntail by relocating MoRE into the RNA-encapsidating Ncore domain. Linker-scanning mutagenesis identified a microdomain in Ncore that tolerates insertions. MoRE relocated to Ncore supported efficient interaction with N, MoRE-deficient Ntails had a dominant-negative effect on bioactivity that was alleviated by insertion of MoRE into Ncore, and recombinant MeV encoding N with relocated MoRE grew efficiently and remained capable of mRNA editing. MoRE in Ncore also restored viability of a recombinant lacking the disordered central Ntail section, but this recombinant was temperature-sensitive, with reduced RdRp loading efficiency and a flattened transcription gradient. These results demonstrate that virus replication requires high-affinity RdRp binding sites in N:RNA, but productive RdRp binding is independent of positional flexibility of MoRE and cis-acting elements in Ntail. Rather, the disordered central Ntail section independent of the presence of MoRE in Ntail steepens the paramyxovirus transcription gradient by promoting RdRp loading and preventing the formation of nonproductive polycistronic viral mRNAs. Disordered Ntails may have evolved as a regulatory element to adjust paramyxovirus gene expression.

Attenuated Infectious Hematopoietic Necrosis Virus with Rearranged Gene Order as Potential Vaccine

The genome of infectious hematopoietic necrosis virus (IHNV), a salmonid novirhabdovirus, has been engineered to modify the gene order and to evaluate the impact on a possible attenuation of the virus in vitro and in vivo By reverse genetics, eight recombinant IHNVs (rIHNVs), termed NxGy according to the respective positions of the nucleoprotein (N) and glycoprotein (G) genes along the genome, have been recovered. All rIHNVs have been fully characterized in vitro for their cytopathic effects, kinetics of replication, and profiles of viral gene transcription. These rIHNVs are stable through up to 10 passages in cell culture. Following bath immersion administration of the various rIHNVs to juvenile trout, some of the rIHNVs were clearly attenuated (N2G3, N2G4, N3G4, and N4G1). The position of the N gene seems to be one of the most critical features correlated to the level of viral attenuation. The induced immune response potential in fish was evaluated by enzyme-linked immunosorbent spot assay (ELISPOT) and seroneutralization assays. The recombinant virus N2G3 induced a strong antibody response in immunized fish and conferred 86% of protection against wild-type IHNV challenge in trout, thus representing a promising starting point for the development of a live attenuated vaccine candidate.

IMPORTANCE

In Europe, no vaccines are available against infectious hematopoietic necrosis virus (IHNV), one of the major economic threats in fish aquaculture. Live attenuated vaccines are conditioned by a sensible balance between attenuation and pathogenicity. Moreover, nonsegmented negative-strain RNA viruses (NNSV) are subject to a transcription gradient dictated by the order of the genes in their genomes. With the perspective of developing a vaccine against IHNV, we engineered various recombinant IHNVs with reordered genomes in order to artificially attenuate the virus. Our results validate the gene rearrangement approach as a potent and stable attenuation strategy for fish novirhabdovirus and open a new perspective for design of vaccines against other NNSV.

A recombinant rabies virus carrying GFP between N and P affects viral transcription in vitro

Several studies have demonstrated the rabies virus to be a perfect potential vaccine vector to insert foreign genes into the target genome. For this study, a green fluorescent protein (GFP) gene was cloned into the rabies virus (RABV) genome between the N and P gene. CT dinucleotide was inserted as intergenic region. The recombinant high egg passage Flury strain (HEP-Flury) of RABV, carrying GFP (rHEP-NP-GFP), was generated in BHK-21 cells using reverse genetics. According to the viral growth kinetics assay, the addition of GFP between N and P gene has little effect on the viral growth compared to the parental strain HEP-Flury. Quantitative real-time PCR (qPCR) indicated that rHEP-NP-GFP showed different viral gene transcription, especially for G gene, compared to HEP-Flury. The same is true for one other recombinant RABV carrying GFP between G and L gene in NA cells. In addition, parent HEP-Flury showed more expression of innate immune-related molecules in NA cells. Compared to HEP-Flury, Western blotting (WB) indicated that insertion of a foreign gene following N gene enhanced the expression of M and G proteins. According to the qPCR and WB, GFP expression levels of rHEP-NP-GFP were significantly higher than rHEP-GFP. This study indicates HEP-Flury as valid vector to express exogenous genes between N and P.

Transcriptional Regulation in Ebola Virus: Effects of Gene Border Structure and Regulatory Elements on Gene Expression and Polymerase Scanning Behavior

The highly pathogenic Ebola virus (EBOV) has a nonsegmented negative-strand (NNS) RNA genome containing seven genes. The viral genes either are separated by intergenic regions (IRs) of variable length or overlap. The structure of the EBOV gene overlaps is conserved throughout all filovirus genomes and is distinct from that of the overlaps found in other NNS RNA viruses. Here, we analyzed how diverse gene borders and noncoding regions surrounding the gene borders influence transcript levels and govern polymerase behavior during viral transcription. Transcription of overlapping genes in EBOV bicistronic minigenomes followed the stop-start mechanism, similar to that followed by IR-containing gene borders. When the gene overlaps were extended, the EBOV polymerase was able to scan the template in an upstream direction. This polymerase feature seems to be generally conserved among NNS RNA virus polymerases. Analysis of IR-containing gene borders showed that the IR sequence plays only a minor role in transcription regulation. Changes in IR length were generally well tolerated, but specific IR lengths led to a strong decrease in downstream gene expression. Correlation analysis revealed that these effects were largely independent of the surrounding gene borders. Each EBOV gene contains exceptionally long untranslated regions (UTRs) flanking the open reading frame. Our data suggest that the UTRs adjacent to the gene borders are the main regulators of transcript levels. A highly complex interplay between the different cis-acting elements to modulate transcription was revealed for specific combinations of IRs and UTRs, emphasizing the importance of the noncoding regions in EBOV gene expression control.

IMPORTANCE

Our data extend those from previous analyses investigating the implication of noncoding regions at the EBOV gene borders for gene expression control. We show that EBOV transcription is regulated in a highly complex yet not easily predictable manner by a set of interacting cis-active elements. These findings are important not only for the design of recombinant filoviruses but also for the design of other replicon systems widely used as surrogate systems to study the filovirus replication cycle under low biosafety levels. Insights into the complex regulation of EBOV transcription conveyed by noncoding sequences will also help to interpret the importance of mutations that have been detected within these regions, including in isolates of the current outbreak.

A Dynein Light Chain 1 Binding Motif in Rabies Virus Polymerase L Protein Plays a Role in Microtubule Reorganization and Viral Primary Transcription

Rabies virus (RABV) polymerase L together with phosphoprotein P forms the PL polymerase complex that is essential for replication and transcription. However, its exact mechanism of action, interactions with cellular factors, and intracellular distribution are yet to be understood. Here by imaging a fluorescently tagged polymerase (mCherry-RABV-L), we show that L accumulates at acetylated and reorganized microtubules (MT). In silico analysis revealed a dynein light chain 1 (DLC1) binding motif in L that could mediate MT binding through dynein motors. As DLC1 binding by polymerase cofactor P is known, we compared the impact of the DLC1-binding motifs in P and L. Viruses with mutations in the respective motifs revealed that both motifs are required for efficient primary transcription, indicating that DLC1 acts as a transcription enhancer by binding to both P and L. Notably, also the levels of cellular DLC1 protein were regulated by both motifs, suggesting regulation of the DLC1 gene expression by both P and L. Finally, disruption of the motif in L resulted in a cell-type-specific loss of MT localization, demonstrating that DLC1 is involved in L-mediated cytoskeleton reorganization. Overall, we conclude that DLC1 acts as a transcription factor that stimulates primary RABV transcription by binding to both P and L. We further conclude that L influences MT organization and posttranslational modification, suggesting a model in which MT manipulation by L contributes to efficient intracellular transport of virus components and thus may serve as an important step in virus replication.

IMPORTANCE

Regulation of rabies virus polymerase complex by viral and cellular factors thus far has not been fully understood. Although cellular dynein light chain 1 (DLC1) has been reported to increase primary transcription by binding to polymerase cofactor phosphoprotein P, the detailed mechanism is unknown, and it is also not known whether the large enzymatic polymerase subunit L is involved. By fluorescence microscopy analysis of fluorescence-tagged rabies virus L, in silico identification of a potential DLC1 binding site in L, and characterization of recombinant rabies virus mutants, we show that a DLC1 binding motif in L is involved in cytoskeleton localization and reorganization, primary transcription regulation by DLC1, and regulation of cellular DLC1 gene expression. By providing evidence for a direct contribution of a DLC1 binding motif in L, our data significantly increase the understanding of rabies virus polymerase regulation and host manipulation by the virus as well.

Everything You Always Wanted to Know About Rabies Virus (But Were Afraid to Ask)

The cultural impact of rabies, the fatal neurological disease caused by infection with rabies virus, registers throughout recorded history. Although rabies has been the subject of large-scale public health interventions, chiefly through vaccination efforts, the disease continues to take the lives of about 40,000-70,000 people per year, roughly 40% of whom are children. Most of these deaths occur in resource-poor countries, where lack of infrastructure prevents timely reporting and postexposure prophylaxis and the ubiquity of domestic and wild animal hosts makes eradication unlikely. Moreover, although the disease is rarer than other human infections such as influenza, the prognosis following a bite from a rabid animal is poor: There is currently no effective treatment that will save the life of a symptomatic rabies patient. This review focuses on the major unanswered research questions related to rabies virus pathogenesis, especially those connecting the disease progression of rabies with the complex dysfunction caused by the virus in infected cells. The recent applications of cutting-edge research strategies to this question are described in detail.

Effects of G-gene Deletion and Replacement on Rabies Virus Vector Gene Expression

The glycoprotein-gene (G gene) -deleted rabies virus (RV) vector is a powerful tool to examine the function and structure of neural circuits. We previously reported that the deletion of the G gene enhances the transgene expression level of the RV vector. However, the mechanism of this enhancement remains to be clarified. We presume that there are two possible factors for this enhancement. The first factor is the glycoprotein of RV, which shows cytotoxicity; thus, may cause a dysfunction in the translation process of infected cells. The second possible factor is the enhanced expression of the L gene, which encodes viral RNA polymerase. In the RV, it is known that the gene expression level is altered depending on the position of the gene. Since G-gene deletion displaces the L gene in the genome, the expression of the L gene and viral transcription may be enhanced. In this study, we compared the transgene expression level and viral transcription of three recombinant RV vectors. The effect of glycoprotein was examined by comparing the viral gene expression of G-gene-intact RV and G-gene-replaced RV. Despite the fact that the L-gene transcription level of these two RV vectors was similar, the G-gene-replaced RV vector showed higher viral transcription and transgene expression level than the G-gene-intact RV vector. To examine the effect of the position of the L gene, we compared the viral gene expression of the G-gene-deleted RV and G-gene-replaced RV. The G-gene-deleted RV vector showed higher L-gene transcription, viral transcription, and transgene expression level than the G-gene-replaced RV vector. These results indicate that G-gene deletion enhances the transgene expression level through at least two factors, the absence of glycoprotein and enhancement of L-gene expression. These findings enable investigators to design a useful viral vector that shows a controlled desirable transgene expression level in applications.

The aberrant gene-end transcription signal of the matrix M gene of human parainfluenza virus type 3 downregulates fusion F protein expression and the F-specific antibody response in vivo

Human parainfluenza virus type 3 (HPIV3), a paramyxovirus, is a major viral cause of severe lower respiratory tract disease in infants and children. The gene-end (GE) transcription signal of the HPIV3 matrix (M) protein gene is identical to those of the nucleoprotein and phosphoprotein genes except that it contains an apparent 8-nucleotide insert. This was associated with an increased synthesis of a readthrough transcript of the M gene and the downstream fusion (F) protein gene. We hypothesized that this insert may function to downregulate the expression of F protein by interfering with termination/reinitiation at the M-F gene junction, thus promoting the production of M-F readthrough mRNA at the expense of monocistronic F mRNA. To test this hypothesis, two similar recombinant HPIV3 viruses from which this insert in the M-GE signal was removed were generated. The M-GE mutants exhibited a reduction in M-F readthrough mRNA and an increase in monocistronic F mRNA. This resulted in a substantial increase in F protein synthesis in infected cells as well as enhanced incorporation of F protein into virions. The efficiency of mutant virus replication was similar to that of wild-type (wt) HPIV3 both in vitro and in vivo. However, the F-protein-specific serum antibody response in hamsters was increased for the mutants compared to wt HPIV3. This study identifies a previously undescribed viral mechanism for attenuating the host adaptive immune response. Repairing the M-GE signal should provide a means to increase the antibody response to a live attenuated HPIV3 vaccine without affecting viral replication and attenuation.

IMPORTANCE

The HPIV3 M-GE signal was previously shown to contain an apparent 8-nucleotide insert that was associated with increased synthesis of a readthrough mRNA of the M gene and the downstream F gene. However, whether this had any significant effect on the synthesis of monocistronic F mRNA or F protein, virus replication, virion morphogenesis, and immunogenicity was unknown. Here, we show that the removal of this insert shifts F gene transcription from readthrough M-F mRNA to monocistronic F mRNA. This resulted in a substantial increase in the amount of F protein expressed in the cell and packaged in the virus particle. This did not affect virus replication but increased the F-specific antibody response in hamsters. Thus, in wild-type HPIV3, the aberrant M-GE signal operates a previously undescribed mechanism that reduces the expression of a major neutralization and protective antigen, resulting in reduced immunogenicity. This has implications for the design of live attenuated HPIV3 vaccines; specifically, the antibody response against F can be elevated by "repairing" the M-GE signal to achieve higher-level F antigen expression, with no effect on attenuation.

Current status of rabies and prospects for elimination

Rabies is one of the most deadly infectious diseases, with a case-fatality rate approaching 100%. The disease is established on all continents apart from Antarctica; most cases are reported in Africa and Asia, with thousands of deaths recorded annually. However, the estimated annual figure of almost 60,000 human rabies fatalities is probably an underestimate. Almost all cases of human rabies result from bites from infected dogs. Therefore, the most cost-effective approach to elimination of the global burden of human rabies is to control canine rabies rather than expansion of the availability of human prophylaxis. Mass vaccination campaigns with parenteral vaccines, and advances in oral vaccines for wildlife, have allowed the elimination of rabies in terrestrial carnivores in several countries worldwide. The subsequent reduction in cases of human rabies in such regions advocates the multidisciplinary One Health approach to rabies control through the mass vaccination of dogs and control of canine populations.

Analysis of the highly diverse gene borders in Ebola virus reveals a distinct mechanism of transcriptional regulation

Ebola virus (EBOV) belongs to the group of nonsegmented negative-sense RNA viruses. The seven EBOV genes are separated by variable gene borders, including short (4- or 5-nucleotide) intergenic regions (IRs), a single long (144-nucleotide) IR, and gene overlaps, where the neighboring gene end and start signals share five conserved nucleotides. The unique structure of the gene overlaps and the presence of a single long IR are conserved among all filoviruses. Here, we sought to determine the impact of the EBOV gene borders during viral transcription. We show that readthrough mRNA synthesis occurs in EBOV-infected cells irrespective of the structure of the gene border, indicating that the gene overlaps do not promote recognition of the gene end signal. However, two consecutive gene end signals at the VP24 gene might improve termination at the VP24-L gene border, ensuring efficient L gene expression. We further demonstrate that the long IR is not essential for but regulates transcription reinitiation in a length-dependent but sequence-independent manner. Mutational analysis of bicistronic minigenomes and recombinant EBOVs showed no direct correlation between IR length and reinitiation rates but demonstrated that specific IR lengths not found naturally in filoviruses profoundly inhibit downstream gene expression. Intriguingly, although truncation of the 144-nucleotide-long IR to 5 nucleotides did not substantially affect EBOV transcription, it led to a significant reduction of viral growth.

IMPORTANCE

Our current understanding of EBOV transcription regulation is limited due to the requirement for high-containment conditions to study this highly pathogenic virus. EBOV is thought to share many mechanistic features with well-analyzed prototype nonsegmented negative-sense RNA viruses. A single polymerase entry site at the 3' end of the genome determines that transcription of the genes is mainly controlled by gene order and cis-acting signals found at the gene borders. Here, we examined the regulatory role of the structurally unique EBOV gene borders during viral transcription. Our data suggest that transcriptional regulation in EBOV is highly complex and differs from that in prototype viruses and further the understanding of this most fundamental process in the filovirus replication cycle. Moreover, our results with recombinant EBOVs suggest a novel role of the long IR found in all filovirus genomes during the viral replication cycle.

Gene order rearrangement of the M gene in the rabies virus leads to slower replication

The matrix protein (M) is one of only five genes in the RV genome and is an important multifunctional protein. Besides to allow for the release of newly replicated virions pairing with G, the M protein also functions in virus replication, pathogenicity, and host cell apoptosis. The goal of present study is to generate recombinant viruses with M gene rearranged, thus laying the foundation for further exploring what will happen when the gene for M is relocated on the RV single-strand RNA. We used rHEP-Flury, an attenuated virus that remains virulent for less than 3 days in sucking mice, to reshuffle the M gene, using an approach that leaves the other viral nucleotide sequence intact. Two viruses with translocated M genes (N1M2 and N1M4) were recovered from each of the rearranged cDNAs, whose gene order is 3'-N-M-P-G-L-5' and 3'-N-P-G-M-L-5' respectively. The growth dynamics of these viruses showed slower replication than the wild-type virus in multiple-step growth curves, but they can grow to a comparable titer in tests of single-step growth curves. Further experimentation with these rearranged viruses will provide insights into the relationships between genome structure and virus phenotypes.

Axonal and subcellular labelling using modified rabies viral vectors

An important aspect of any neural circuit is the placement of its output synapses, at levels ranging from macroscopic to subcellular. The many new molecular tools for locating and manipulating synapses are limited by the viral vectors available for delivering them. Adeno-associated viruses are the best current means of labeling and manipulating axons and synapses, but they have never expressed more than one transgene highly enough to label fine axonal structure while also labeling or perturbing synapses. Their slow expression also makes them incompatible with retrograde and transsynaptic vectors, preventing powerful combinatorial experiments. Here we show that deletion-mutant rabies virus can be specifically targeted to cells local to an injection site, brightly labeling axons even when coexpressing two other transgenes. We demonstrate several novel capabilities: simultaneously labeling axons and presynaptic terminals, labeling both dendrites and postsynaptic densities, and simultaneously labeling a region’s inputs and outputs using coinjected vectors.

Rabies virus vector transgene expression level and cytotoxicity improvement induced by deletion of glycoprotein gene

The glycoprotein (G) of rabies virus (RV) is required for binding to neuronal receptors and for viral entry. G-deleted RV vector is a powerful tool for investigating the organization and function of the neural circuits. It gives the investigator the ability to genetically target initial infection to particular neurons and to control trans-synaptic propagation. In this study we have quantitatively evaluated the effect of G gene deletion on the cytotoxicity and transgene expression level of the RV vector. We compared the characteristics of the propagation-competent RV vector (rHEP5.0-CVSG-mRFP) and the G-deleted RV vector (rHEP5.0-ΔG-mRFP), both of which are based on the attenuated HEP-Flury strain and express monomeric red fluorescent protein (mRFP) as a transgene. rHEP5.0-ΔG-mRFP showed lower cytotoxicity than rHEP5.0-CVSG-mRFP, and within 16 days of infection we found no change in the basic electrophysiological properties of neurons infected with the rHEP5.0-ΔG-mRFP. The mRFP expression level of rHEP5.0-ΔG-mRFP was much higher than that of rHEP5.0-CVSG-mRFP, and 3 days after infection the retrogradely infected neurons were clearly visualized by the expressed fluorescent protein without any staining. This may be due to the low cytotoxicity and/or the presumed change in the polymerase gene (L) expression level of the G-deleted RV vector. Although the mechanisms remains to be clarified, the results of this study indicate that deletion of the G gene greatly improves the usability of the RV vector for studying the organization and function of the neural circuits by decreasing the cytotoxicity and increasing the transgene expression level.

Revealing the secrets of neuronal circuits with recombinant rabies virus technology

An understanding of how the brain processes information requires knowledge of the architecture of its underlying neuronal circuits, as well as insights into the relationship between architecture and physiological function. A range of sophisticated tools is needed to acquire this knowledge, and recombinant rabies virus (RABV) is becoming an increasingly important part of this essential toolbox. RABV has been recognized for years for its properties as a synapse-specific trans-neuronal tracer. A novel genetically modified variant now enables the investigation of specific monosynaptic connections. This technology, in combination with other genetic, physiological, optical, and computational tools, has enormous potential for the visualization of neuronal circuits, and for monitoring and manipulating their activity. Here we will summarize the latest developments in this fast moving field and provide a perspective for the use of this technology for the dissection of neuronal circuit structure and function in the normal and diseased brain.

Reverse Genetics of Mononegavirales: The Rabies Virus Paradigm

The neurotropic rabies virus (RABV) is a prototype member of the Mononegavirales order of viruses and is the most significant human pathogen of the Rhabdoviridae family. A reverse genetics system for RABV was established almost 20 years ago, providing a paradigm for other Mononegavirales members as well. The availability of engineered recombinant viruses opened a new era to study common aspects of Mononegavirales biology and specific aspects of the unique lifestyle and pathogenesis of individual members. Above all, the knowledge gained has allowed engineering of beneficial biomedical tools such as viral vectors, vaccines, and tracers. In this chapter, the development of the classical rabies virus reverse genetics approach is described, and some of the most exciting biomedical applications for recombinant RABV and other Mononegavirales are briefly addressed.

Molecular analysis of the mutational effects of Thai street rabies virus with increased virulence in mice after passages in the BHK cell line

QS-BHK-P7, street rabies virus, after passages in the BHK cell line, had an in vitro phenotype that distinguished it from its parental virus. Both viruses caused lethal infection in mice by central nervous system inoculation; however, only QS-BHK-P7 killed mice by the intramuscular route. We found four mutations, S23R and H424P in ectodomain of the glycoprotein (G), I1711 V in the polymerase genes, and another at the non-coding region between the phosphoprotein and matrix protein genes of QS-BHK-P7. None of the mutations in the G gene occurred in previously reported pathogenic determinants. The roles of mutations in particular non-coding regions remain to be elucidated.

Phylogenetic analysis of partial RNA-polymerase blocks II and III of Rabies virus isolated from the main rabies reservoirs in Brazil

This study describes the results of the sequencing and analysis of segments of Blocks II and III of the RNA polymerase L gene of Rabies virus isolates from different reservoir species of Brazil. The phylogenetic relations of the virus were determined and a variety of species-specific nucleotides were found in the analyzed areas, but the majority of these mutations were found to be synonymous. However, an analysis of the putative amino acid sequences were shown to have some characteristic mutations between some reservoir species of Brazil, indicating that there was positive selection in the RNA polymerase L gene of Rabies virus. On comparing the putative viral sequences obtained from the Brazilian isolates and other Lyssavirus, it was determined that amino acid mutations occurred in low-restriction areas. This study of the L gene of Rabies virus is the first to be conducted with samples of virus isolates from Brazil, and the results obtained will help in the determination of the phylogenetic relations of the virus.

The 3' untranslated region of the rabies virus glycoprotein mRNA specifically interacts with cellular PCBP2 protein and promotes transcript stability

Viral polymerase entry and pausing at intergenic junctions is predicted to lead to a defined polarity in the levels of rhabdovirus gene expression. Interestingly, we observed that the rabies virus glycoprotein mRNA is differentially over-expressed based on this model relative to other transcripts during infection of 293T cells. During infection, the rabies virus glycoprotein mRNA also selectively interacts with the cellular poly(rC)-binding protein 2 (PCBP2), a factor known to influence mRNA stability. Reporter assays performed both in electroporated cells and in a cell-free RNA decay system indicate that the conserved portion of the 3' UTR of the rabies virus glycoprotein mRNA contains an RNA stability element. PCBP2 specifically interacts with reporter transcripts containing this 72 base 3' UTR sequence. Furthermore, the PCBP2 interaction is directly associated with the stability of reporter transcripts. Therefore, we conclude that PCBP2 specifically and selectively interacts with the rabies virus glycoprotein mRNA and that this interaction may contribute to the post-transcriptional regulation of glycoprotein expression.

[Rhabdoviruses]

The family Rhabdoviridae has a non-segmented single stranded negative-sense RNA and its genome ranges in size from approximately 11 kb to almost 16 kb. It is one of the most ecologically diverse families of RNA viruses with members infecting a wide range of organisms. The five structural protein genes are arranged in the same linear order (3'-N-P-M-G-L-5') and may be interspersed with one more additional accessory gene. For many years, a full of knowledge of the rhabdoviridae has been established on extensive studies of two kinds of prototype viruses; vesicular stomatitis virus (VSV) and rabies virus (RABV). Among them, the genus Lyssavirus includes RABV and rabies-related viruses naturally infect mammals and chiropterans via bite-exposure by rabid animals and finally cause fatal encephalitis. In this review, we describe the sketch of the various virological features of the Rhabdoviridae, especially focusing on VSV and RABV.

A unique transcription mode of rabies virus high egg passage-Flury strain detected in infected baby hamster kidney-21 cells

The transcription mode of rabies virus high egg passage-Flury (HEP) strain was examined and compared with that of Evelyn Rokitniki Abelseth (ERA) strain by northern blot analysis using rabies virus gene-specific probes. The ERA strain was shown to exclusively produce monocistronic mRNAs in transcription. All combinations of multicistronic transcripts, including five monocistronic mRNAs, were detected in the viral RNA transcripts of HEP strain. It was concluded that the unique transcription mode is not due to the nucleotide structure of the genome RNA template, but rather to the viral RNA polymerase of HEP strain. The viral polymerase of HEP strain read through the gene junction at a high frequency. The HEP strain has been passaged many times in chick embryo and cultured cells, and has adapted to propagate well in the baby hamster kidney-21 (BHK-21) cells. Through these passages in various hosts, the HEP strain has acquired a unique transcription mode that might have an advantage in amplification of the virus.

Rabies virus transcription and replication

Rabies virus (RABV) is a negative-stranded RNA virus. Its genome is tightly encapsidated by the viral nucleoprotein (N) and this RNA-N complex is the template for transcription and replication by the viral RNA-dependent RNA polymerase (L) and its cofactor, the phosphoprotein (P). We present molecular, structural, and cellular aspects of RABV transcription and replication. We first summarize the characteristics and molecular biology of both RNA synthesis processes. We then discuss biochemical and structural data on the viral proteins (N, P, and L) and their interactions with regard to their role in viral transcription and replication. Finally, we review evidence that rabies viral transcription and replication take place in cytoplasmic inclusion bodies formed in RABV-infected cells and discuss the role of this cellular compartmentalization.

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.

Limited interference at the early stage of infection between two recombinant novirhabdoviruses: viral hemorrhagic septicemia virus and infectious hematopoietic necrosis virus

The genome sequence of a hypervirulent novirhabdovirus, viral hemorrhagic septicemia virus (VHSV) French strain 23-75, was determined. Compared to the genome of the prototype Fil3 strain, a number of substitutions, deletions, and insertions were observed. Following the establishment of a plasmid-based minigenome replication assay, recombinant VHSV (rVHSV) was successfully recovered. rVHSV exhibits wild-type-like growth properties in vitro as well as in vivo in rainbow trout. The dispensable role of NV for the novirhabdovirus replication was confirmed by generating rVHSV-DeltaNV, in which the NV gene was deleted. This deletion mutant was shown to be as debilitated as that previously described for infectious hematopoietic necrosis virus (IHNV), a distantly related novirhabdovirus (S. Biacchesi, M. I. Thoulouze, M. Bearzotti, Y. X. Yu, and M. Bremont, J. Virol. 74:11247-11253, 2000). Recombinant VHSV and IHNV expressing tdTomato and GFP(max) reporter genes, respectively, were generated, demonstrating the potential of these rhabdoviruses to serve as viral vectors. Interestingly, rIHNV-GFP(max) could be recovered using the replicative complex proteins of either virus, whereas rVHSV-Tomato could be recovered only by using its own replicative complex, reflecting that the genome signal sequences of VHSV are relatively distant from those of IHNV and do not allow their cross-recognition. Moreover, the use of heterologous protein combinations underlined the importance of strong protein-protein interactions for the formation of a functional ribonucleoprotein complex. The rIHNV-GFP(max) and rVHSV-Tomato viruses were used to simultaneously coinfect cell monolayers. It was observed that up to 74% of the cell monolayer was coinfected by both viruses, demonstrating that a limited interference phenomenon exists during the early stage of primary infection, and it was not mediated by a cellular antiviral protein or by some of the viral proteins.

Generation of recombinant European bat lyssavirus type 1 and inter-genotypic compatibility of lyssavirus genotype 1 and 5 antigenome promoters

Bat lyssaviruses (Fam. Rhabdoviridae) represent a source for the infection of terrestial mammals and the development of rabies disease. Molecular differences in the replication of bat and non-bat lyssaviruses and their contribution to pathogenicity, however, are unknown. One reason for this is the lack of reverse genetics systems for bat-restricted lyssaviruses. To investigate bat lyssavirus replication and host adaptation, we developed a reverse genetics system for European bat lyssavirus type 1 (EBLV-1; genotype 5). This was achieved by co-transfection of HEK-293T cells with a full-length EBLV-1 genome cDNA and expression plasmids for EBLV-1 proteins, resulting in recombinant EBLV-1 (rEBLV-1). Replication of rEBLV-1 was comparable to that of parental virus, showing that rEBLV-1 is a valid tool to investigate EBLV-1 replication functions. In a first approach, we tested whether the terminal promoter sequences of EBLV-1 are genotype-specific. Although genotype 1 (rabies virus) minigenomes were successfully amplified by EBLV-1 helper virus, in the context of the complete virus, only the antigenome promoter (AGP) sequence of EBLV-1 was replaceable, as indicated by comparable replication of rEBLV-1 and the chimeric virus. These analyses demonstrate that the terminal AGPs of genotype 1 and genotype 5 lyssaviruses are compatible with those of the heterologous genotype.

Rhabdovirus evasion of the interferon system

The family Rhabdoviridae contains important pathogens of humans, livestock, and crops, including the insect-transmitted vesicular stomatitis virus (VSV) and the neurotropic rabies virus (RV), which is directly transmitted between mammals. In spite of a highly similar organization of RNA genomes, proteins, and virus particles, cell biology of VSV and RV is divergent in several aspects, particularly with respect to their interplay with the cellular host defense. While infection with both rhabdoviruses is recognized via viral triphosphate RNAs by the cytoplasmic RNA helicase/translocase RIG-I, the viral counteractions to limit the response are contrasting. VSV infection is characterized by a rapid general shutdown of host gene expression and severe cytopathic effects, due to multiple activities of the matrix (M) protein affecting host polymerase functions and mRNA nuclear export, and by rapid and high-level virus replication. In contrast, RV spread and transmission relies on preserving the integrity of host cells, particularly of neurons. While a general cell shutdown by RV M is not observed, RV phosphoprotein (P) has developed independent functions to interfere with activation of IRFs and with STAT signaling. The molecular mechanisms employed are different from those of the paramyxovirus P gene products serving similar functions, and illustrate evolution of IFN antagonists to specifically support virus survival in the natural niches.

Complete sequence analysis of rice transitory yellowing virus and its comparison to rice yellow stunt virus

Rice transitory yellowing virus (RTYV), a member of the genus Nucleorhabdovirus, is closely related to or synonymous with rice yellow stunt virus (RYSV). To clarify the relationship between RTYV and RYSV, we determined the nucleotide sequence of the RTYV genome. The RTYV genome consists of 14,029 nucleotides. The overall nucleotide identity between RTYV and RYSV was 98.5%, and the deduced amino acid sequence identities between the seven genes in RTYV and RYSV ranged from 82.3 to 99.7%. The sequence information from RTYV revealed that these two viruses should be categorized as members of the same species rather than distinct species.

The cell biology of rabies virus: using stealth to reach the brain

Rabies virus, the prototypical neurotropic virus, causes one of the most lethal zoonotic diseases. According to official estimates, over 55,000 people die of the disease annually, but this is probably a severe underestimation. A combination of virulence factors enables the virus to enter neurons at peripheral sites and travel through the spinal cord to the brain of the infected host, where it often induces aggression that facilitates the transfer of the virus to a new host. This Review summarizes the current knowledge of the replication cycle of rabies virus and virus- host cell interactions, both of which are fundamental elements in our quest to understand the life cycle of rabies virus and the pathogenesis of rabies.

Characterization of a single-cycle rabies virus-based vaccine vector

Recombinant rabies virus (RV)-based vectors have demonstrated their efficacy in generating long-term, antigen-specific immune responses in murine and monkey models. However, replication-competent viral vectors pose significant safety concerns due to vector pathogenicity. RV pathogenicity is largely attributed to its glycoprotein (RV-G), which facilitates the attachment and entry of RV into host cells. We have developed a live, single-cycle RV by deletion of the G gene from an RV vaccine vector expressing HIV-1 Gag (SPBN-DeltaG-Gag). Passage of SPBN-DeltaG-Gag on cells stably expressing RV-G allowed efficient propagation of the G-deleted RV. The in vivo immunogenicity data comparing single-cycle RV to a replication-competent control (BNSP-Gag) showed lower RV-specific antibodies; however, the overall isotype profiles (IgG2a/IgG1) were similar for the two vaccine vectors. Despite this difference, mice immunized with SPBN-DeltaG-Gag and BNSP-Gag mounted similar levels of Gag-specific CD8(+) T-cell responses as measured by major histocompatibility complex class I Gag-tetramer staining, gamma interferon-enzyme-linked immunospot assay, and cytotoxic T-cell assay. Moreover, these cellular responses were maintained equally at immunization titers as low as 10(3) focus-forming units for both RV vaccine vectors. CD8(+) T-cell responses were significantly enhanced by a boost with a single-cycle RV complemented with a heterologous vesicular stomatitis virus glycoprotein. These findings demonstrate that single-cycle RV is an effective alternative to replication-competent RV vectors for future development of vaccines for HIV-1 and other infectious diseases.

Interferon response and viral evasion by members of the family rhabdoviridae

Like many animal viruses, those of the Rhabdoviridae family, are able to antagonize the type I interferon response and cause disease in mammalian hosts. Though these negative-stranded RNA viruses are very simple and code for as few as five proteins, they have been seen to completely abrogate the type I interferon response early in infection. In this review, we will discuss the viral organization and type I interferon evasion of rhabdoviruses, focusing on vesicular stomatitis virus (VSV) and rabies virus (RABV). Despite their structural similarities, VSV and RABV have completely different mechanisms by which they avert the host immune response. VSV relies on the matrix protein to interfere with host gene transcription and nuclear export of anti-viral mRNAs. Alternatively, RABV uses its phosphoprotein to interfere with IRF-3 phosphorylation and STAT1 signaling. Understanding the virus-cell interactions and viral proteins necessary to evade the immune response is important in developing effective vaccines and therapeutics for this viral family.

A temperature sensitive VSV identifies L protein residues that affect transcription but not replication

To investigate the polymerase components selectively involved in transcription versus replication of vesicular stomatitis virus (VSV), we sequenced the polymerase gene of a conditionally RNA defective, temperature sensitive VSV: ts(G)114, which has a phenotype upon shift from permissive to non-permissive temperature of shut-down of mRNA transcription and unaffected genome replication. Sequence analysis of the ts(G)114 L gene identified three altered amino acid residues in the L protein. These three changes were specifically engineered individually and in combinations into a functional cDNA clone encoding the VSV genome and tested for association with the temperature sensitive and RNA defective phenotypes in the background of recovered engineered viruses. The data presented in this study show a specific amino acid substitution in domain II of the VSV L protein that significantly affects total RNA synthesis, but when in combination with two additional amino acid substitutions identified in the ts(G)114 L protein, leads to a specific reduction in mRNA transcription, but not replication.

Characterization of Ebolavirus regulatory genomic regions

For filoviruses, such as Ebolavirus and the closely related Marburgvirus, transcriptional regulation is poorly understood. The open reading frames (ORFs) that encode the viral proteins are separated by regulatory regions composed of the 3' nontranslated region (NTR) of the upstream gene, highly conserved transcription stop and start signals, and the 5'NTR of the downstream gene. The conserved transcription stop and start signals either overlap, or they are separated by intergenic regions (IGRs) of different lengths. To assess the contribution of the regulatory regions to transcription, we established bicistronic minireplicons in which these regions were flanked by upstream and downstream ORFs, the Ebolavirus leader and trailer regions, and by T7 RNA polymerase promoter and ribozyme sequences. We found that the individual viral regulatory regions differ in their ability to direct protein synthesis from the upstream or downstream ORFs. Deletion or modification of the NTRs, IGRs, or transcription stop and start signals affected protein expression levels to various extents; for example, 5'NTRs appear to affect efficient protein expression from the downstream ORF, whereas 3'NTRs seem to attenuate protein expression from the upstream ORF. Overall, our data suggest that the regulation of Ebolavirus protein levels is complex.