Two‐step chromosomal control of tumorigenicity of chinese hamster cells in nude mice

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Abstract
A simple method for microinjecting isolated chromosomes into a single living cell under an inverted microscope has been developed. Of the 368 injected cells, 85 were able to form a colony and could be cloned. Clones of Chinese hamster V79 cells microinjected with chromosomes isolated from murine D56 cells [V79 (D56) cells] were tested for tumorigenicity in immunodeficient nude mice and for colony‐forming ability in soft agar.Untreated recipient V79 cells were highly tumorigenic and had a high colony‐forming ability in soft agar. In contrast, two out of the 21 microinjected clones tested were non‐tumorigenic in nude mice and had only weak colony‐forming ability in soft agar.The chromosome banding pattern was analyzed in microinjected clones and tumors derived from cells of these clones. In cells of the two non‐tumorigenic clones, a telocentric chromosome 1 (t1) was specifically involved in translocations with other chromosomes or chromosome fragments. In all tumor cells obtained from nude mice, a supernumerary piece or a whole biarmed chromosome 14 (b14) was specifically found. The results suggest that the t1 chromosome bears the gene which controls in vitro transformation and that the additional genetic change, i.e. the extra piece of b14 chromosome, was required for tumor formation in vivo.