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Point mutations in polypeptide VP1 of foot-and-mouth disease virus affect mouse virulence and BHK21 cell
Abstract:
Virus produced in the first four days after infection of a BHK21 culture was shown to differ from that produced later in the infection. The early virus caused large plaques in IB-RS-2 cell sheets, had a slow cytopathic effect in BHK21 cultures and showed a high virulence for suckling mice. In contrast, the late virus caused small plaques, was rapid in its cytopathic effect and was of low virulence for mice. Comparison between one clone each of the early and late virus showed that no change in immunogenic specificity had taken place, but that charge changes had occurred both in VP3 and in the large trypsin-resistant fragment of VP1. The early, large plaquing clone gave rise spontaneously to small plaquing virus during the destructive phase of a single passage in BHK21 cultures. Conversely, the late, small plaquing clone gave rise to large plaquing virus after a single passage in mice. Each new virus was cloned and it was shown that they differed in VP1. This indicated that missense mutations in the genome coding for the trypsin resistant fragment of VP1 were responsible for the biological changes observed.
Insights
Early and late-stage viruses exhibit distinct biological properties, with mutations in VP1 protein explaining observed virulence and plaque size changes. These findings highlight viral evolution dynamics.
Area of Science:
- Virology
- Molecular Biology
- Cell Biology
Background:
- Viral replication dynamics can lead to the emergence of distinct viral populations within a host.
- Understanding these changes is crucial for comprehending viral pathogenesis and evolution.
Purpose of the Study:
- To investigate the biological and molecular differences between early and late-stage viruses produced after infection.
- To identify the genetic basis for observed phenotypic variations in viral clones.
Main Methods:
- Infection of BHK21 and IB-RS-2 cell cultures with viral isolates.
- Plaque assays and cytopathic effect observation.
- Virulence assessment in suckling mice.
- Protein analysis (VP1, VP3) using trypsin digestion and charge shift assays.
- Viral cloning and sequencing.
Main Results:
- Early-stage virus exhibited large plaques, slow cytopathic effect, and high mouse virulence, while late-stage virus showed small plaques, rapid cytopathic effect, and low mouse virulence.
- Immunogenic specificity remained unchanged, but charge alterations were detected in VP3 and the VP1 trypsin-resistant fragment.
- Spontaneous interconversion between large and small plaque variants occurred during passage in cell cultures and mice.
- Differences in VP1, specifically missense mutations in the trypsin-resistant fragment, correlated with observed biological changes.
Conclusions:
- Missense mutations in the VP1 gene's trypsin-resistant fragment are responsible for the observed biological variations in viral virulence and plaque morphology.
- Viral populations can rapidly evolve distinct phenotypes through genetic mutations during host passage.