Proteins induced in tissue culture by four isolates of Theiler's murine encephalomyelitis virus

Protein mutations revealed by two-dimensional electrophoresis

High-resolution two-dimensional electrophoresis (2DE) can resolve many hundreds of proteins present in complex mixtures depending on the method of detection. These proteins can be characterised qualitatively, with respect to their electrophoretic mobilities (i.e. charge and apparent molecular mass) and quantitatively, using densitometry, to determine their amounts. There has been a widespread application of 2DE in the analysis and characterisation of protein mutations for a range of organisms. This review presents examples of the use of 2DE to study naturally occurring protein mutations and polymorphisms as well as the characterisation of induced protein mutations in prokaryotes and eukaryotes. Examples are presented to illustrate the use of 2DE to detect mutations affecting the electrophoretic mobility and biosynthesis of individual proteins as well as mutations leading to global alterations in cellular protein synthesis. The advantages and disadvantages of 2DE in the detection of protein mutations are discussed.

Synthesis of long viral complementary DNA from 7.5 Kb poly A+ RNA templates

The poly A+ RNA of the WW and GDVII virus isolates, belonging to the Theiler's murine encephalomyelitis virus group, were used as templates for cDNA synthesis. Since several secondary structures were present along these viral RNAs the reverse transcriptase was prematurely displaced from the RNA templates and only short cDNA molecules could be synthesized. Therefore a reliable and reproducible procedure for the synthesis of long cDNA transcripts, that can be directly used for cloning into respective plasmid or phage vectors, was developed. The precise conditions and kinetics of the several enzymatic reactions were studied. The use of methylmercury hydroxide for first strand synthesis, a correct choice of Klenow polymerase for second strand synthesis and the use of vertical gel electrophoresis in combination with zone centrifugation for removal of the excess linkers were found to be of paramount importance for the synthesis of long, up to intact, 7.5 Kb cDNA transcripts.

Fractionation of Theiler's virus-infected BHK21 cell homogenates: isolation of virus-induced membranes

A purified fraction containing unique membranes entrapping virions was isolated from homogenates of cells infected with the DA strain of Theiler's virus, after high-speed centrifugation through a sucrose gradient. This fraction, sedimented at 45-50% sucrose, was only found in cells infected with the DA strain but not in cells infected with the GDVII strain of Theiler's virus or in mock-infected cells. Immunogold staining of the membranes entrapping virions, using antivirus IgG antibodies, revealed that the membranes entrapping virions did not incorporate viral capsid antigens.

Analysis of the complete nucleotide sequence of the picornavirus Theiler's murine encephalomyelitis virus indicates that it is closely related to cardioviruses

Theiler's murine encephalomyelitis viruses (TMEV) are naturally occurring enteric pathogens of mice which constitute a separate serological group within the picornavirus family. Persistent TMEV infection in mice provides a relevant experimental animal model for the human demyelinating disease multiple sclerosis. To provide information about the TMEV classification, genome organization, and protein processing map, we determined the complete nucleotide sequence of the TMEV genome and deduced the amino acid sequence of the polyprotein coding region. The RNA genome, which is typical of the picornavirus family, is 8,098 nucleotides long. The 5' untranslated region is 1,064 nucleotides long (making it the longest in the picornavirus family after the aphthoviruses) and lacks a poly(C) tract. Computer-generated comparison of the 5' and 3' noncoding regions and polyprotein revealed the highest level of nucleotide and predicted amino acid identity between the TMEV and the cardioviruses encephalomyocarditis virus (EMCV) and Mengo virus. The TMEV polyprotein, which appears to be processed like EMCV since the amino acids flanking the putative proteolytic cleavage sites have been conserved, begins with a short leader peptide followed by 11 other gene products in the standard L-4-3-4 picornavirus arrangement. Because of these similarities, we propose that the TMEV be grouped with the cardioviruses. However, since TMEV and EMCV have different biophysical properties and show no cross-neutralization, they most likely belong in a separate cardiovirus subgroup.

Theiler's virus replication in isolated Schwann cell cultures

Theiler's murine encephalomyelitis viruses causing both fatal encephalitis (GDVII virus) and chronic demyelinating disease (WW virus) are capable of replicating in isolated Schwann cell cultures. Light microscopy combined with immunohistochemical staining of viral antigens revealed that large numbers of Schwann cells infected with the two viruses show cytopathic effect (rounding) and contain viral antigens. Electron microscopy of virus-infected Schwann cells shows that the morphological alterations that the cells undergo following infection by the two virus isolates are different. In the early stages of GDVII and WW virus infection, different inclusion bodies are formed in the cells cytoplasm. At late stages of the infection GDVII virions are found in all infected cells and are arranged in crystalline arrays around inclusion bodies. In contrast, in WW virus-infected Schwann cells only in few cells virions were observed and they appeared aligned between two membrane units.

In vitro cytotoxicity and demyelination induced by Theiler viruses in cultures of spinal cord slices

The cytopathic effects caused by Theiler viruses to myelinated organotypic spinal cord cultures was studied by light and electron microscopy. Heavily myelinated cultures, 2-3 weeks in vitro were infected with WW and GD VII viruses. Mock infection served as control. On light microscopy cytopathic effects and demyelination became evident about 16-17 hr after infection. Demyelination observed in WW virus-infected cultures was much more pronounced than in cultures infected with GD VII viruses. The myelin in mock-infected cultures remained undamaged. Electron microscopy revealed that in control cultures cells were intact, exhibiting numerous synapses and a network of axons enwrapped by multilayered myelin sheaths. Virus-infected spinal cord slices showed that a more severe cytotoxicity was caused by GD VII virus than by WW virus. The cytopathology included accumulation of cytoplasmatic vacuoles, margination of chromatin, synapse and cell disintegration, and various degrees of demyelination. Several GD VII virions were observed, arranged in crystalline arrays, mainly in electron-opaque cells, but not within axons. WW virions on the other hand were only occasionally encountered.

Localization of a neutralization site of Theiler's murine encephalomyelitis viruses

Theiler's murine encephalomyelitis viruses (TMEV) are picornaviruses that produce enteric and neurological diseases in mice. Subgroup TO strains of TMEV cause persistent infections with demyelination, while subgroup GDVII strains neither persist nor demyelinate. We produced neutralizing monoclonal antibodies (mAbs) to clarify the mechanisms of persistence and demyelination. Some of the neutralizing mAbs reacted with isolated VP1 on Western blots, while others were conformation specific. The neutralization site for the former TMEV mAbs was on the VP1 trypsin cleavage site of the intact virion. The neutralization site for the conformation-specific mAbs was distinct and was not affected by trypsin. Trypsin treatment of subgroup TO strains increased their infectivity for L cells, whereas the infectivity of subgroup GDVII strains was decreased by trypsin treatment. Subpopulations of virus in subgroup TO-infected tissue culture cells and in infected mouse brain homogenates contained VP1-cleaved virus; this VP1-cleaved virus gave rise to a large persistent fraction in neutralization tests when it was reacted with VP1-specific mAbs. These findings have implications regarding the pathogenesis of subgroup TO demyelinating disease. TMEV VP1 cleavage may be important for virus persistence because of disruption of a major neutralization epitope. The change in virus surface structure caused by VP1 cleavage may affect cell binding and lead to altered cytotropism. Immunocytes, which have been implicated in subgroup TO demyelination, may provide a source for proteases for VP1 cleavage.

Neutralizing monoclonal antibodies to Theiler's murine encephalomyelitis viruses

Theiler's murine encephalomyelitis viruses (TMEV) are serologically related picornaviruses which cause both enteric and neurological disease in mice. The biological activities of TMEV vary between the two different TMEV subgroups (TO and GDVII) and with different passage histories of the same TMEV strain (e.g., mouse brain-passed versus tissue culture-passed DA strain of the TO subgroup). We raised neutralizing monoclonal antibodies (mAbs) against tissue culture-passed DA and GDVII strains of TMEV. We produced two mAbs against the DA strain which neutralized all members of the TO subgroup, but not the GDVII subgroup strains (GDVII and FA); these two DA mAbs reacted similarly with both mouse brain-passed DA and tissue culture-passed DA. Of six neutralizing GDVII mAbs, four reacted only to GDVII and FA, whereas two neutralized TO strains as well. These mAbs demonstrate the presence of TMEV group-specific as well as subgroup-specific neutralization and substantiate the division of TMEV into two distinct subgroups. On Western immunoblots one of the two DA mAbs reacted against isolated DA VP1, two GDVII mAbs (which were TMEV group specific) reacted against isolated GDVII VP1 and DA VP1, and the other DA mAb and four other GDVII mAbs required an intact virion conformation for reactivity. An analysis of the epitopes recognized by these mAbs may elucidate sites important in TMEV biological activities.

Comparison of structural and nonstructural proteins of virulent and less virulent Theiler's virus isolates using two-dimensional gel electrophoresis

The Theiler's murine encephalomyelitis viruses (TMEV) are important neurotropic picornaviruses because they persist in the central nervous system (CNS) and produce an inflammatory demyelinating disease in the mouse, their natural host. Insight into the pathogenesis of this disease may come from studying the genetic and biochemical compositions of these viruses; therefore, in this report, the structural and nonstructural proteins specified by both highly and less virulent TMEV were examined. Using two-dimensional gel electrophoresis, structural and nonstructural proteins, originating from each of the three regions of the picornavirus genome (Kitamura et al., 1981; Rueckert and Wimmer, 1984), from nine TMEV isolates were compared on the basis of isoelectric points (pI). Proteins of two virulent TMEV (GDVII and FA viruses) had almost indistinguishable pI values, whereas two of the three major capsid proteins of the less virulent TMEV varied considerably. For example, the structural proteins VP1 and VP3 from seven less virulent viruses ranged from pI 6.3 to 6.9 and 6.5 to 8.3, respectively. On the other hand, the pI values of VP2 and nonstructural proteins from the less virulent TMEV varied relatively little. In general, structural proteins of each TMEV group had pI ranges unique to their respective biological group, while most nonstructural proteins were similar for all TMEV. The virus-specified proteins of Vilyuisk virus, which is serologically related to the TMEV and a possible cause of encephalomyelitis in man, had pI values similar to the less virulent TMEV. Finally, VP3 not only showed the greatest variation in pI among the less virulent TMEV, but it also was preferentially radioiodinated in intact virus from each of the two biological groups using the lactoperoxidase technique.

Persistent and acute central nervous system infections are caused by Theiler's murine encephalomyelitis viruses which differ in RNA composition but code for only slightly different proteins

The RNA and proteins for four representatives of the two subgroups of Theiler's murine encephalomyelitis viruses were studied. The large RNase T1-resistant oligonucleotides, when mapped along the RNA molecules, were found to be differently distributed in the two subgroups. Replicative form RNAs of two representatives were partially denatured, and the denaturation maps obtained were found to be similar but not identical. In addition, the analysis of the tryptic maps of the capsid proteins of all four isolates revealed that only small differences in the peptide map patterns exist among these viruses. The correlation of these findings with the pathogenicity of Theiler's viruses is discussed.