The M25 gene products are critical for the cytopathic effect of mouse cytomegalovirus

Ivana Kutle,Sarah Sengstake,Mandy Glaß,Martina Dezeljin,Martin Messerle,Anne Binz,Luka Čičin-Šain,Rudolf Bauerfeind,Corinna Templin,Kirsten A Keyser,Tobias Kubsch,Beate Sodeik

doi:10.1038/s41598-017-15783-x

Abstract

Cell rounding is a hallmark of the cytopathic effect induced by cytomegaloviruses. By screening a panel of deletion mutants of mouse cytomegalovirus (MCMV) a mutant was identified that did not elicit cell rounding and lacked the ability to form typical plaques. Altered cell morphology was assigned to the viral M25 gene. We detected an early 2.8 kb M25 mRNA directing the synthesis of a 105 kDa M25 protein, and confirmed that a late 3.1 kb mRNA encodes a 130 kDa M25 tegument protein. Virions lacking the M25 tegument protein were of smaller size because the tegument layer between capsid and viral envelope was reduced. The ΔM25 mutant did not provoke the rearrangement of the actin cytoskeleton observed after wild-type MCMV infection, and isolated expression of the M25 proteins led to cell size reduction, confirming that they contribute to the morphological changes. Yields of progeny virus and cell-to-cell spread of the ΔM25 mutant in vitro were diminished and replication in vivo was impaired. The identification of an MCMV gene involved in cell rounding provides the basis for investigating the role of this cytopathic effect in CMV pathogenesis.

Highlights

Productive infection by many viruses leads to distinct morphological changes in infected cells, collectively known as cytopathic effect (CPE)
This phenotype was observed on C127I epithelial cells as well as on murine embryonic fibroblasts (MEF) and liver sinusoidal endothelial cells (Supplementary Fig. S1)
In this study we identified and characterized an Mouse CMV (MCMV) mutant that lacks the ability to elicit cell rounding

Summary

Introduction

Productive infection by many viruses leads to distinct morphological changes in infected cells, collectively known as cytopathic effect (CPE). CPE could be a passive side effect of viral infection, resulting from cellular stress caused by a massive production of virus particles; the existence of non-cytopathic viruses indicates that virus replication is not necessarily associated with morphological changes or cytotoxicity. The lytic, productive infection cycle of human cytomegalovirus (HCMV), the prototypic member of the β-herpesviruses, is characterized by typical rounding and enlargement of infected cells[6]. The latter aspect is so characteristic that the virus received its name based on this property. A first assessment of the ΔM25 mutant in vivo revealed that the M25 gene has an important role in viral pathogenesis in the infected host

Methods

Results

Conclusion