Hras1‐selected, chromosome‐mediated transformants vary in phenotype in vitro and tumorigenic potential in vivo

Transfection of mouse C127 cells with mitotic chromosomes isolated from a human EJ bladder carcinoma cell line gave rise, at high frequency, to foci of transformed cells. Independent, HRAS 1‐selected chromosome‐mediated transformants displayed distinctive cellular morphologies in monolayer culture and colony‐forming abilities in low‐melting‐point agarose. Subcutaneous inoculation of neonatally thymec‐tomized, Ara‐C‐protected, total‐body‐irradiated CBA mice was used to compare the tumorigenic potential of each transformant. Significant quantitative and qualitative differences in tumorigenicity were found between transformants which correlated with differences in malignant phenotype observed in vitro. The sensitivity of the tumorigenicity assay is such that rare transformation events can be selected directly in vivo.