Studies of genetic transmission of mammary tumour virus by C3Hf mice.

By radioimmunoassay (RIA) mammary tumour virus (MTV) antigens were detected in individual milk samples of C3Hf mice, (♀BALB/c × ♂ C3Hf)Fl mice and (♀C3Hf × ♂ BALB/c)Fl mice; milk samples of BALB/c mice were negative. In the segregating backcross I population, ♀ BALB/c × ♂ (♀BALB/c × ♀ C3Hf) viral antigens were found in the milk of 93 out of 169 mice (55%). In the Bc II population (daughters of Bc I mothers and BALB/c fathers) two groups were distinguished. In the first group, derived from positive Bc I mothers, 55 out of 110 mice (50%) had detectable levels of viral antigens in the milk. In the second group, progeny of negative Bc I mothers, 1 mouse out of 47 was positive. These data are consistent with the assumption that one dominant gene is responsible for the presence of viral antigens in the milk of C3Hf mice. This gene (Mtv-1) seems to be linked with the albino locus situated on chromosome 7; the recombination percentage was about 29. In the first experiment with Bc I mice a significant difference was found between the tumour ages of the mice with virus-positive milk and of the mice with virus-negative milk: all mice (18) with viral antigens in the milk developed mammary tumours at an age ranging from 7 to 18 months, whereas in only 7 out of 16 mice with virus-negative milk were mammary tumours found before the age of 21 months. Viral antigens were detectable (by RIA) in the tumours of mice of both subgroups; however, the amounts (mU/mg tumour) were significantly lower in the tumours derived from mice with virus-negative milk. Although MTV-L of C3Hf mothers could be transmitted to BALB/c mice by foster-nursing, viral antigens could not be detected in milk samples collected prior to the third lactation period; thus an influence on the data of extrachromosomally transmitted MTV-L is unlikely.