Mouse mammary tumor virus (MMTV) antigen(s) are present on B lymphocytes of BALB/c mice

Spleen specific expression of an MMTV related transcript associated with the Mtv-6 locus in BALB/c mice

We have detected an MMTV related transcript which is expressed in a spleen specific manner in BALB/cHeA mice. Using a recombinant inbred series between BALB/cHeA and STS/A mice (C X S RI series) we have identified RNA associated with the Mtv-3 locus of the STS/A strain. This transcript initiates at the same site in the MMTV LTR as already reported for Mtv-2 and Mtv-8. The novel spleen specific MMTV transcript in the BALB/cHeA strain has a different structure as compared to the transcripts associated with the Mtv-2, Mtv-3, or Mtv-8 loci. We have tentatively identified the Mtv-6 locus as the source of these unique transcripts.

Direct detection of exogenous mouse mammary tumor virus sequences in lymphoid cells of BALB/cfC3H female mice

The presence of exogenous mouse mammary tumor virus (MMTV) (C3H) DNA sequences in lymphoid tissue (spleen, bone marrow, and thymus) and nonlymphoid tissue (liver and kidney) of BALB/cfC3H female mice was directly assessed by DNA hybridization methods. Lymphoid tissues were found positive for integrated MMTV(C3H) sequences in females as young as 4 weeks. In most samples, the level of splenic MMTV(C3H) infection was low (2 to 5%). Infection remained throughout the life of the animal. The percentage of spleen samples found positive for exogenous viral infection was significantly higher in females bearing mammary tumors, whether virgin or multiparous. Liver and kidney DNAs were negative for exogenous MMTV sequences, suggesting tissue type selectivity in MMTV infection.

Expression and demethylation of germinally-transmitted BALB/c mouse mammary tumor virus DNA in Abelson MuLV B-lymphoid cell lines

Murine mammary tumor virus (MMTV) RNA expression, DNA organization and DNA demethylation were examined in BALB/c B-lymphoid cell lines produced by transformation with the Abelson murine leukemia virus (AbMuLV). The MMTV DNA sequences in AbMuLV B cell lines, based on restriction mapping with EcoRI, PstI, BglII, BamHI and SacI and molecular hybridization with cloned probes of the MMTV LTR, gag-pol or env gene regions, were identical to the germinally-transmitted MMTV DNA complement of BALB/c mice. Several AbMuLV B cell lines expressed MMTV poly(A+)-RNA at detectable levels. MMTV poly(A+)-RNA for the env gene, 3.8 kb, and the long terminally redundant (LTR) region, 1.7 kb, were detected in some AbMuLV B cell lines. MMTV DNA sequences in the AbMuLV B cell lines were at least partially sensitive to digestion by the methylation-sensitive restriction endonucleases HhaI and HpaII. HhaI-sensitive sites were present in Units I, II and III of the germinally-transmitted MMTV DNA and were localized specifically near the 5' end of the 5' and 3' LTRs of both Units II and III. HpaII-sensitive sites were localized near the 3' end of the 3' LTRs of Units II and III, and at a cellular site 2.1 kbp 5' to the 5' LTR. These observations demonstrate that the germ line MMTV DNA sequences of BALB/c mice are expressed in cells of B lymphocyte origin, and suggest a correlation between MMTV RNA expression and selective demethylation in the LTR regions of germinally-transmitted MMTV DNA sequences.