Mouse mammary tumour virus

Mouse mammary tumor virus
Virus classification
Group:	Group VI (ssRNA-RT)
Order:	Unassigned
Family:	Retroviridae
Subfamily:	Orthoretrovirinae
Genus:	Betaretrovirus
Species:	Mouse mammary tumor virus

Mouse mammary tumor virus (MMTV) is a milk-transmitted retrovirus like the HTL viruses, HI viruses, and BLV. It belongs to the genus Betaretrovirus. MMTV was formerly known as Bittner virus, and previously the "milk factor", referring to the extra-chromosomal vertical transmission of murine breast cancer by adoptive nursing, demonstrated in 1936, by John Joseph Bittner while working at the Jackson Laboratory in Bar Harbor, Maine. Bittner established the theory that a cancerous agent, or "milk factor", could be transmitted by cancerous mothers to young mice from a virus in their mother's milk. The majority of mammary tumors in mice are caused by mouse mammary tumor virus.

Several mouse strains carry the virus endogenously, but it is also transmitted vertically via milk from mother to pup. It is contained as a DNA provirus integrated in the DNA of milk lymphocytes. The viruses become transported through the gastrointestinal tract to the Peyer's patches where they infect the new host's macrophages, and then lymphocytes.

The mouse mammary tumor virus (MMTV) has formerly been classified as a simple retrovirus; however, it has recently been established, that MMTV encodes an extra self-regulatory mRNA export protein, Rem, with resemblance to the Human Immunodeficiency Virus HIV Rev protein, and is therefore the first complex murine retrovirus to be documented.

MMTV codes for the retroviral structural genes and additionally for a superantigen. This stimulates T lymphocytes with a certain type of V beta chain in their T cell receptor, which in turn stimulates B cell proliferation increasing the population of cells that can be infected. During puberty, the virus enters the mammary glands with migrating lymphocytes and infects proliferating mammary gland epithelial cells.

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Wikipedia