Minute virus of mice

The Minute Virus of Mice (MVM) is the prototype virus of the Protoparvovirus genus within the Parvoviridae family of viruses.^[1][2] MVM exists in two variant forms: MVMp, which is the prototype strain, infects cells of fibroblast origin, while MVMi, the immunosuppressive strain, infects T lymphocytes.^[3] MVM is a common infection in laboratory mice due to its highly contagious nature.^[4] The virus can be shed from infected mice via feces and urine, but also via fomites and nasal secretions.^[4] Typically there are no clinical signs of infection, however, experimental infection can cause multiple organ damage during fetal development or shortly after birth.^[4] While MVM infection may result in pathology of infected mice, the infection is more likely to cause problems for the ongoing study the mice are being used for as the immune system will be activated, the activity of T-lymphocytes and B-lymphocytes will be altered and tumor formation may be suppressed.^[4]

Transcription profile

During replication MVM utilizes three open reading frames (ORFs) and produces three distinct mRNA transcripts which are referred to as R1, R2 and R3.^[5] R1, produced from ORF 3, is translated into non-structural protein 1 (NS1).^[5] mRNA transcript R2, produces non-structural protein 2 (NS2) by splicing the 5-prime end of ORF3 with ORF2, which is found within the 3-prime end of ORF.^[5] The resulting NS2 protein is thus composed of spliced 5-prime and 3-prime alternative ORF sections of NS1.^[5] Finally, the R3 transcript produces capsid proteins VP1 and VP2, which requires transcription from the P38 promoter, in contrast to the P4 promoter used for transcripts R1 and R2.^[6]

Non-structural protein functions

NS1 functions as a required replication protein and is known to have helicase activity,^[7] ATPase activity ^[7] and nickase activity.^[2] Specifically, the nickase activity is required to resolve replication intermediate telomeres on the right-hand of the genome.^[2] NS2 is known to exist in several spliced forms (isoforms) termed NS2-P, -Y and –L due to differences in the C-terminus of the isoforms as a result of alternative splicing.^[8] NS2 is known to exist is both the cytoplasm and nucleus as well as in phosphorylated and non-phosphorylated forms.^[8] In addition, NS2 is required for efficient infection in its natural murine host, but is dispensable in experimental infection in human cell lines.^[8] Although not fully understood, in murine A9 fibroblasts NS2 interacts with nuclear export factor Crm1 resulting in efficient nuclear egress of progeny virions.^[8]

DNA damage response

MVM induces a DNA damage response (DDR) during infection which is required for effective replication.^[9] The ATM pathway is exclusively activated with a primarily Chk2-mediated response.^[9] It is not known if viral proteins or active viral replication activate the DDR, but UV-inactivated MVM does not induce a response ^[9] suggesting that presence of MVM virions or MVM genome alone cannot cause the observed DDR activation.

Commercial Uses

The Minute virus of Mice is currently the smallest virus that can be easily titrated to high levels; as such it is commercially used as a "worst case" example of a very small virus.^[10][11]

References