Restriction endonuclease studies of hyperplastic outgrowth lines from BALB/cfC3H mouse hyperplastic mammary nodules

The DNA's isolated from five mouse hyperplastic mammary gland outgrowth lines from BALB/cfC3H mice were digested with the restriction endonucleases PsTI, BamHI, or EcoRI; electrophoresed; and analyzed by Southern blotting and autoradiography. Proviral DNA sequences from the acquired C3H mouse mammary tumor virus were detected in the DNA of all five lines, indicating that they were infected. The DNA of the five hyperplastic lines contained more EcoRI and BamHI mouse mammary tumor virus proviral DNA fragments than did DNA from normal organs, suggesting that the hyperplastic tissues were composed of more homogeneous cell populations than was lactating mammary gland. Each hyperplastic line had unique and reproducible BamHI and EcoRI restriction (integration) patterns which were stable over as many as seven transplant generations. Three sublines, which originated from the same hyperplastic alveolar nodule, had unique integration patterns but also shared several fragments. On the basis of these observations, we propose that mouse mammary "hyperplasias" are clonal dominant premalignant neoplasms.