Germ line integration of moloney leukemia virus: effect of homozygosity at the m-mulV locus.

Mice genetically transmitting the exogenous Moloney leukemia virus (M-MuLV) have been previously derived. These animals carried one copy of M-MuLV DNA in their germ line and were heterozygous for the M-MuLV locus (Jaenisch, 1976). Experiments were performed to investigate whether homozygosity at the M-MuLV locus would be compatible with normal development. Animals heterozygous for the M-MuLV locus were mated [female (+/-) X male(+/-)] and the genotype of the offspring was analyzed. Molecular hybridization experiments revealed three classes of offspring carrying two copies (++), one copy (+/-) and no (--) M-MuLV-specific DNA sequences, respectively, in their liver DNA. Genetic experiments indicated that males of the first class transmitted the virus to 100% of their offspring, males of the second class to 50% and males of the third class not at all when mated with normal females. These results demonstrated that homozygosity at the M-MuLV locus has no detectable effect on normal development of the animals and that the M-MuLV gene is transmitted from one generation to the next strictly according to Mendelian expectations. Development of M-MuLV-induced leukemia is not influenced by the genotype of these animals--that is, animals carrying two or one copies of M-MuLV in their germ line or animals congenitally infected from the mother developed disease at similar rates.