Comparison of mouse mammary tumor virus-specific DNA in inbred, wild and Asian mice, and in tumors and normal organs from inbred mice

Abstract

We have measured DNA related to the genome of mouse mammary tumor virus in normal organs from laboratory, feral and Asian mice, and in mammary tumors from laboratory mice, by annealing MMT § § Abbreviations used: MMT, mouse mammary tumor; MMT viral cDNA, single-stranded DNA complementary to the mouse mammary tumor virus genome; C 0t , product of DNA concentration and time. viral cDNA to cellular DNA. Normal organs from most laboratory strains (e.g. BALB/c, RIII, A and BALB/cfC3H) contain 5 to 9 copies of MMT viral DNA per diploid cell, but GR mice, previously shown to transmit a virulent strain of MMT virus genetically (Muhlbock & Bentvelzen, 1969) contain 9 to 14 copies of viral DNA per cell. The number of copies of viral DNA in mammary tumors from RIII and BALB/cfC3H mice exposed to milk-borne virus range from that found in normal organs to about 30 copies per cell; the increments in copy number imply viral infection. Feral mice and a subspecies of Mus musculus (M. musculus molossinus) contain half the number of copies of MMT viral DNA found in laboratory mice. Thermal denaturation studies with DNA from normal organs of all tested strains of M. musculus and from RIII mammary tumors did not reveal significant differences among the viral nucleotide sequences. Two Asian species of mice, M. caroli and M. cervicolor, contain limited portions of the viral genome in their DNA. About 30% of MMT viral cDNA annealed to M. cervicolor DNA; virus-related sequences are approximately 30 to 50-fold reiterated in this species and diverged from viral sequences in proportion to the divergence between M. musculus and M. cervicolor unique-sequence DNA (about 3 to 5%). About 10% of MMT viral cDNA annealed to highly diverged sequences which are 3- to 16-fold reiterated in M. caroli DNA. The results suggest that MMT viral DNA has been present in the germ line of Mus at least since the evolution of Asian species (3 to 5 × 10 6 years ago) and appears to evolve at least as fast as cellular unique-sequence DNA.