Pseudorabies virus-based gene delivery to rat embryonic spinal cord grafts

Transneuronal Circuit Analysis with Pseudorabies Viruses

Our ability to understand the function of the nervous system is dependent upon defining the connections of its constituent neurons. Development of methods to define connections within neural networks has always been a growth industry in the neurosciences. Transneuronal spread of neurotropic viruses currently represents the best means of defining synaptic connections within neural networks. The method exploits the ability of viruses to invade neurons, replicate, and spread through the intimate synaptic connections that enable communication among neurons. Since the method was first introduced in the 1970s, it has benefited from an increased understanding of the virus life cycle, the function of viral genomes, and the ability to manipulate the viral genome in support of directional spread of virus and the expression of transgenes. In this article, we review these advances in viral tracing technology and the ways in which they may be applied for functional dissection of neural networks. © 2023 The Authors. Current Protocols published by Wiley Periodicals LLC. Basic Protocol 1: Retrograde infection of CNS circuits by peripheral injection of virus Basic Protocol 2: Transneuronal analysis by intracerebral injection Alternate Protocol 1: Transneuronal analysis with multiple recombinant strains Alternate Protocol 2: Conditional replication and spread of PRV Alternate Protocol 3: Conditional reporters of PRV infection and spread Alternate Protocol 4: Reporters of neural activity in polysynaptic circuits Support Protocol 1: Growing and titering a PRV viral stock Support Protocol 2: Immunohistochemical processing and detection Support Protocol 3: Dual-immunofluorescence localization.

An Integrated Sequencing Approach for Updating the Pseudorabies Virus Transcriptome

In the last couple of years, the implementation of long-read sequencing (LRS) technologies for transcriptome profiling has uncovered an extreme complexity of viral gene expression. In this study, we carried out a systematic analysis on the pseudorabies virus transcriptome by combining our current data obtained by using Pacific Biosciences Sequel and Oxford Nanopore Technologies MinION sequencing with our earlier data generated by other LRS and short-read sequencing techniques. As a result, we identified a number of novel genes, transcripts, and transcript isoforms, including splice and length variants, and also confirmed earlier annotated RNA molecules. One of the major findings of this study is the discovery of a large number of 5′-truncations of larger putative mRNAs being 3′-co-terminal with canonical mRNAs of PRV. A large fraction of these putative RNAs contain in-frame ATGs, which might initiate translation of N-terminally truncated polypeptides. Our analyses indicate that CTO-S, a replication origin-associated RNA molecule is expressed at an extremely high level. This study demonstrates that the PRV transcriptome is much more complex than previously appreciated.

Repair of spinal cord injury with neuronal relays: From fetal grafts to neural stem cells

Spinal cord injury (SCI) disrupts the long axonal tracts of the spinal cord leading to devastating loss of function. Cell transplantation in the injured spinal cord has the potential to lead to recovery after SCI via a variety of mechanisms. One such strategy is the formation of neuronal relays between injured long tract axons and denervated neurons. The idea of creating a neuronal relay was first proposed over 25 years ago when fetal tissue was first successfully transplanted into the injured rodent spinal cord. Advances in labeling of grafted cells and the development of neural stem cell culturing techniques have improved the ability to create and refine such relays. Several recent studies have examined the ability to create a novel neuronal circuit between injured axons and denervated targets. This approach is an alternative to long-distance regeneration of damaged axons that may provide a meaningful degree of recovery without direct recreation of lost pathways. This brief review will examine the contribution of fetal grafting to current advances in neuronal grafting. Of particular interest will be the ability of transplanted neurons derived from fetal grafts, neural precursor cells and neural stem cells to reconnect long distance motor and sensory pathways of the injured spinal cord. This article is part of a Special Issue entitled SI: Spinal cord injury.

Transneuronal circuit analysis with pseudorabies viruses

Our ability to understand the function of the nervous system is dependent upon defining the connections of its constituent neurons. Development of methods to define connections within neural networks has always been a growth industry in the neurosciences. Transneuronal spread of neurotropic viruses currently represents the best means of defining synaptic connections within neural networks. The method exploits the ability of viruses to invade neurons, replicate, and spread through the intimate synaptic connections that enable communication among neurons. Since the method was first introduced in the 1970s, it has benefited from an increased understanding of the virus life cycle, the function of viral genome, and the ability to manipulate the viral genome in support of directional spread of virus and the expression of transgenes. In this unit, we review these advances in viral tracing technology and the way in which they may be applied for functional dissection of neural networks.

Ex vivo infection of human embryonic spinal cord neurons prior to transplantation into adult mouse cord

Background

Genetically modified pseudorabies virus (Prv) proved suitable for the delivery of foreign genes to rodent embryonic neurons ex vivo and maintaining foreign gene expression after transplantation into spinal cord in our earlier study. The question arose of whether human embryonic neurons, which are known to be more resistant to Prv, could also be infected with a mutant Prv. Specifically, we investigated whether a mutant Prv with deleted ribonucleotide reductase and early protein 0 genes has the potential to deliver marker genes (gfp and β-gal) into human embryonic spinal cord neurons and whether the infected neurons maintain expression after transplantation into adult mouse cord.

Results

The results revealed that the mutant Prv effectively infected human embryonic spinal cord neurons ex vivo and the grafted cells exhibited reporter gene expression for several weeks. Grafting of infected human embryonic cells into the spinal cord of immunodeficient (rnu-/rnu-) mice resulted in the infection of some of the host neurons.

Discussion

These results suggest that Prv is suitable for the delivery of foreign genes into transplantable human cells. This delivery method may offer a new approach to use genetically modified cells for grafting in animal models where spinal cord neuronal loss or axon degeneration occurs.

Whole-genome analysis of pseudorabies virus gene expression by real-time quantitative RT-PCR assay

Background

Pseudorabies virus (PRV), a neurotropic herpesvirus of pigs, serves as an excellent model system with which to investigate the herpesvirus life cycle both in cultured cells and in vivo. Real-time RT-PCR is a very sensitive, accurate and reproducible technique that can be used to detect very small amounts of RNA molecules, and it can therefore be applied for analysis of the expression of herpesvirus genes from the very early period of infection.

Results

In this study, we have developed and applied a quantitative reverse transcriptase-based real-time PCR technique in order to profile transcription from the whole genome of PRV after lytic infection in porcine kidney cells. We calculated the relative expression ratios in a novel way, which allowed us to compare different PRV genes with respect to their expression dynamics, and to divide the PRV genes into distinct kinetic classes. This is the first publication on the whole-genome analysis of the gene expression of an alpha-herpesvirus by qRT2-PCR. We additionally established the kinetic properties of uncharacterized PRV genes and revised or confirmed data on PRV genes earlier examined by traditional methods such as Northern blot analysis. Our investigations revealed that genes with the same expression properties form clusters on the PRV genome: nested overlapping genes belong in the same kinetic class, while most convergent genes belong in different kinetic classes. Further, we detected inverse relationships as concerns the expressions of EP0 and IE180 mRNAs and their antisense partners.

Conclusion

Most (if not all) PRV genes begin to be expressed from the onset of viral expression. No sharp boundary was found between the groups of early and late genes classified on the basis of their requirement for viral DNA synthesis. The expressions of the PRV genes were analyzed, categorized and compared by qRT2-PCR assay, with the average of the minimum cycle threshold used as a control for the calculation of a particular R value. In principle, this new calculation technique is applicable for the analysis of gene expression in all temporally changing genetic systems.

Herpesvirus-mediated delivery of a genetically encoded fluorescent Ca(2+) sensor to canine cardiomyocytes

We report the development and application of a pseudorabies virus-based system for delivery of troponeon, a fluorescent Ca²⁺ sensor to adult canine cardiomyocytes. The efficacy of transduction was assessed by calculating the ratio of fluorescently labelled and nonlabelled cells in cell culture. Interaction of the virus vector with electrophysiological properties of cardiomyocytes was evaluated by the analysis of transient outward current (I_to), kinetics of the intracellular Ca²⁺ transients, and cell shortening. Functionality of transferred troponeon was verified by FRET analysis. We demonstrated that the transfer efficiency of troponeon to cultured adult cardiac myocytes was virtually 100%. We showed that even after four days neither the amplitude nor the kinetics of the I_to current was significantly changed and no major shifts occurred in parameters of [Ca²⁺]_i transients. Furthermore, we demonstrated that infection of cardiomyocytes with the virus did not affect the morphology, viability, and physiological attributes of cells.

Effect of herpesvirus infection on pancreatic duct cell secretion

AIM: To examine the effect of acute infection caused by herpesvirus (pseudorabies virus, PRV) on pancreatic ductal secretion.

METHODS: The virulent Ba-DupGreen (BDG) and non-virulent Ka-RREp0lacgfp (KEG) genetically modified strains of PRV were used in this study and both of them contain the gene for green fluorescent protein (GFP). Small intra/interlobular ducts were infected with BDG virus (107 PFU/mL for 6 h) or with KEG virus (1010 PFU/mL for 6 h), while non-infected ducts were incubated only with the culture media. The ducts were then cultured for a further 18 h. The rate of HCO3- secretion [base efflux -J(B-)] was determined from the buffering capacity of the cells and the initial rate of intracellular acidification (1) after sudden blockage of basolateral base loaders with dihydro-4,4-diisothiocyanatostilbene-2,2-disulfonic acid (500 mmol/L) and amiloride (200 mmol/L), and (2) after alkali loading the ducts by exposure to NH4Cl. All the experiments were performed in HCO3--buffered Ringer solution at 37°C (n = 5 ducts for each experimental condition). Viral structural proteins were visualized by immunohistochemistry. Virally-encoded GFP and immunofluorescence signals were recorded by a confocal laser scanning microscope.

RESULTS: The BDG virus infected the majority of accessible cells of the duct as judged by the appearance of GFP and viral antigens in the ductal cells. KEG virus caused a similarly high efficiency of infection. After blockage of basolateral base loaders, BDG infection significantly elevated -J(B^-) 24 h after the infection, compared to the non-infected group. However, KEG infection did not modify -J(B^-). After alkali loading the ducts, -J(B^-) was significantly elevated in the BDG group compared to the control group 24 h after the infection. As we found with the inhibitor stop method, no change was observed in the group KEG compared to the non-infected group.

CONCLUSION: Incubation with the BDG or KEG strains of PRV results in an effective infection of ductal epithelial cells. The BDG strain of PRV, which is able to initiate a lytic viral cycle, stimulates HCO3- secretion in guinea pig pancreatic duct by about four- to fivefold, 24 h after the infection. However, the KEG strain of PRV, which can infect, but fails to replicate, has no effect on HCO3- secretion. We suggest that this response of pancreatic ducts to virulent PRV infection may represent a defense mechanism against invasive pathogens to avoid pancreatic injury.

Novel tracing paradigms--genetically engineered herpesviruses as tools for mapping functional circuits within the CNS: present status and future prospects

The mammalian CNS is composed of an extremely complex meshwork of highly ordered interconnections among billions of neurons. To understand the diverse functions of this neuronal network we need to differentiate between functionally related and nonrelated elements. A powerful labeling method for defining intricate neural circuits is based on the utilization of neurotropic herpesviruses, including pseudorabies virus and herpes simplex virus type 1. The recent development of genetically engineered tracing viruses can open the way toward the conception of novel tract-tracing paradigms. These new-generation tracing viruses may facilitate the clarification of problems, which were inaccessible to earlier approaches. This article first presents a concise review of the general aspects of neuroanatomical tracing protocols. Subsequently, it discusses the molecular biology of alpha-herpesviruses, and the genetic manipulation and gene expression techniques that are utilized for the construction of virus-based tracers. Finally, it describes the current utilization of genetically modified herpesviruses for circuit analysis, and the future directions in their potential applications.