Cerebellar pathology in transgenic mice expressing the pseudorabies virus immediate-early protein IE180

Single amino acid mutation of nectin-1 provides remarkable resistance against lethal pseudorabies virus infection in mice

An approach to genetically engineered resistance to pseudorabies virus (PRV) infection was examined by using a mouse model with defined point mutation in primary receptor for alphaherpesviruses, nectin-1, by the CRISPR/Cas9 system. It has become clear that phenylalanine at position 129 of nectin-1 is important for binding to viral glycoprotein D (gD), and mutation of phenylalanine 129 to alanine (F129A) prevents nectin-1 binding to gD and virus entry in vitro. Here, to assess the antiviral potential of the single amino acid mutation of nectin-1, F129A, in vivo, we generated genome-edited mutant mouse lines; F129A and 135 knockout (KO). The latter, 135 KO used as a nectin-1 knockout line for comparison, expresses a carboxy-terminal deleted polypeptide consisting of 135 amino acids without phenylalanine 129. In the challenge with 10 LD50 PRV via intranasal route, perfect protection of disease onset was induced by expression of the mutation of nectin-1, F129A (survival rate: 100% in F129A and 135 KO versus 0% in wild type mice). Neither viral DNA/antigens nor pathological changes were detected in F129A, suggesting that viral entry was prevented at the primary site in natural infection. In the challenge with 50 LD50 PRV, lower but still strong protective effect against disease onset was observed (survival rate: 57% in F129A and 75% in 135 KO versus 0% in wild type mice). The present results indicate that single amino acid mutation of nectin-1 F129A provides significant resistance against lethal pseudorabies.

Expression of the immediate early IE180 protein under the control of the hTERT and CEA tumor-specific promoters in recombinant pseudorabies viruses: Effects of IE180 protein on promoter activity and apoptosis induction

Since the pseudorabies virus (PRV) genome encodes for a single immediate-early protein, IE180, we reasoned that this strong transactivating protein could represent a key regulatory switch that could be genetically manipulated in order to alter its tropism towards cancer cells. We therefore initiated studies to test whether the human telomerase reverse transcriptase (hTERT) and carcinoembryonic antigen (CEA) tumor promoters could functionally replace the IE180 promoter. We show that both promoters can functionally substitute the IE180 promoter in plasmid constructs and recombinant viruses, and observed that IE180 differentially auto-regulated each promoter tested, with PRV IE180 negatively regulating the hTERT promoter but positively hyper-activating the CEA promoter. Interestingly, we also observed that the recombinant PRV-TER and PRV-CEA viruses preferentially replicated in diverse cancer cell lines compared to control non-cancer cells, and the PRV-CEA was capable of additionally inducing a profound apoptotic phenotype which we correlated to the overexpression of IE180.

Characterization of a replication-incompetent pseudorabies virus mutant lacking the sole immediate early gene IE180

The alphaherpesvirus pseudorabies virus (PRV) encodes a single immediate early gene called IE180. The IE180 protein is a potent transcriptional activator of viral genes involved in DNA replication and RNA transcription. A PRV mutant with both copies of IE180 deleted was constructed 20 years ago (S. Yamada and M. Shimizu, Virology 199:366–375, 1994, doi:10.1006/viro.1994.1134), but propagation of the mutant depended on complementing cell lines that expressed the toxic IE180 protein constitutively. Recently, Oyibo et al. constructed a novel set of PRV IE180 mutants and a stable cell line with inducible IE180 expression (H. Oyibo, P. Znamenskiy, H. V. Oviedo, L. W. Enquist, A. Zador, Front. Neuroanat. 8:86, 2014, doi:10.3389/fnana.2014.00086), which we characterized further here. These mutants failed to replicate new viral genomes, synthesize immediate early, early, or late viral proteins, and assemble infectious virions. The PRV IE180-null mutant did not form plaques in epithelial cell monolayers and could not spread from primary infected neurons to second-order neurons in culture. PRV IE180-null mutants lacked the property of superinfection exclusion. When PRV IE180-null mutants infected cells first, subsequent superinfecting viruses were not blocked in cell entry and formed replication compartments in epithelial cells, fibroblasts, and neurons. Cells infected with PRV IE180-null mutants survived as long as uninfected cells in culture while expressing a fluorescent reporter gene. Transcomplementation with IE180 in epithelial cells restored all mutant phenotypes to wild type. The conditional expression of PRV IE180 protein enables the propagation of replication-incompetent PRV IE180-null mutants and will facilitate construction of long-term single-cell-infecting PRV mutants for precise neural circuit tracing and high-capacity gene delivery vectors.

Pseudorabies virus (PRV) is widely used for neural tracing in animal models. The virus replicates and spreads between synaptically connected neurons. Current tracing strains of PRV are cytotoxic and kill infected cells. Infected cells exclude superinfection with a second virus, limiting multiple virus infections in circuit tracing. By removing the only immediate early gene of PRV (called IE180), the mutant virus will not replicate or spread in epithelial cells, fibroblasts, or neurons. The wild-type phenotype can be restored by transcomplementation of infected cells with IE180. The PRV IE180-null mutant can express fluorescent reporters for weeks in cells with no toxicity; infected cells survive as long as uninfected cells. Infection with the mutant virus allows superinfection of the same cell with a second virus that can enter and replicate. The PRV IE180-null mutant will permit conditional long-term tracing in animals and is a high-capacity vector for gene delivery.

Molecular cloning and characterization of the pseudorabies virus US1 gene

Using polymerase chain reaction, a 1050-bp sequence of the US1 gene was amplified from the pseudorabies virus (PRV) Becker strain genome; identification of the US1 gene was confirmed by further cloning and sequencing. Bioinformatics analysis indicated that the PRV US1 gene encodes a putative polypeptide with 349 amino acids. The encoded protein, designated PICP22, had a conserved Herpes_IE68 domain, which was found to be closely related with the herpes virus immediate early regulatory protein family and is highly conserved among the counterparts encoded by Herpes_IE68 genes. Multiple nucleic acid sequence and amino acid sequence alignments suggested that the product of PRV US1 has a relatively higher homology with ICP22-like proteins of genus Varicellovirus than with those of other genera of Alphaherpesvirinae. In addition, phylogenetic analysis showed that PRV US1 has a close evolutionary relationship with members of the genus Varicellovirus, especially Equid herpes virus 1 (EHV-1), EHV-4 and EHV-9. Antigen prediction indicated that several potential B-cell epitopes are located in PICP22. Also, subcellular localization analysis demonstrated that PICP22 is predominantly located in the cytoplasm, suggesting that it might function as a cytoplasmic-targeted protein.

Anti pseudorabies virus activity of kumazasa extract

Sasa veitchii or "kumazasa" has been used for the preservation of food, or preventing bacterial activity. However, the antiviral activity of kumazasa is poorly understood. In the present study, the antiviral activity of kumazasa extract (KE) was assessed by the plaque reduction assay for the pseudorabies virus (PRV). KE reduced 99% of the plaque formation of PRV at concentrations of 1.2%, showing that KE inhibited PRV adsorption to cells and IE180 expression. The polysaccharide fraction of KE showed a concentration dependent inhibition of PRV plaque formation. We conclude that KE possesses potent anti PRV activity, and the candidate responsible for the antiviral property was the polysaccharide fraction.

Development of an anatomical technique for visualizing the mode of climbing fiber innervation in Purkinje cells and its application to mutant mice lacking GluRδ2 and Ca(v)2.1

In the adult cerebellum, a single climbing fiber (CF) innervates proximal dendrites of Purkinje cells (PCs). This monoinnervation is established by the developmental elimination of surplus CFs through homosynaptic competition among multiply innervating CFs and heterosynaptic competition between CFs and parallel fibers, i.e., granule cell axons innervating distal PC dendrites. Although the developmental process of CF monoinnervation and defects in it in mutant and experimental animal models have been extensively studied by electrophysiological techniques, for quite some time this subject was poorly understood from a morphological perspective due to a lack of neuroanatomical methods that could distinguish CFs with different neuronal origins. Soon after the identification of type 2 vesicular glutamate transporter (VGluT2) that selectively detects CF terminals in the molecular layer, we developed a novel method of combined anterograde tracer labeling and VGluT2 immunohistochemistry. This method enables us to identify the mode (mono vs. multiple) of CF innervation and the site of multiple innervation. Since then, we have applied this method to various kinds of gene-manipulated mice manifesting ataxia and other cerebellar phenotypes. In this review, we summarize experimental procedures for the combined tracer/VGluT2 labeling method, and then introduce what we have learned by applying this method in studies on the role of GluRδ2 and Ca(v)2.1 in CF monoinnervation. This method has provided informative anatomical correlates to electrophysiological data and vice versa, and will extend our knowledge of the molecular and cellular mechanisms for the development, plasticity, degeneration, and repair of the CF-PC projection system.

Motor-coordination-dependent learning, more than others, is impaired in transgenic mice expressing pseudorabies virus immediate-early protein IE180

The cerebellum in transgenic mice expressing pseudorabies virus immediate-early protein IE180 (TgIE96) was substantially diminished in size, and its histoarchitecture was severely disorganized, resulting in severe ataxia. TgIE96 mice can therefore be used as an experimental model to study the involvement of cerebellar circuits in different learning tasks. The performance of three-month-old TgIE96 mice was studied in various behavioral tests, including associative learning (classical eyeblink conditioning), object recognition, spatial orientation (water maze), startle response and prepulse inhibition, and passive avoidance, and compared with that of wild-type mice. Wild-type and TgIE96 mice presented similar reflexively evoked eyeblinks, and acquired classical conditioned eyelid responses with similar learning curves for both trace and delay conditioning paradigms. The two groups of mice also had similar performances during the object recognition test. However, they showed significant differences for the other three tests included in this study. Although both groups of animals were capable of swimming, TgIE96 mice failed to learn the water maze task during the allowed time. The startle response to a severe tone was similar in both control and TgIE96 mice, but the latter were unable to produce a significant prepulse inhibition. TgIE96 mice also presented evident deficits for the proper accomplishment of a passive avoidance test. These results suggest that the cerebellum is not indispensable for the performance of classical eyeblink conditioning and for object recognition tasks, but seems to be necessary for the proper performance of water maze, prepulse inhibition, and passive avoidance tests.