On suppression of tumorigenicity in hybrid and cybrid mouse cells.

The contribution of cytoplasm in the suppression of tumorigenicity was examined in cybrids constructed by fusing whole tumorigenic mouse mammary cells (Balb/c, cell line C2B2 from line MT29240) with enucleated nontumorigenic cells (BALB/c, cell line THOC from clone A31). Chloramphenicol resistance was used as a cytoplasmic marker in selecting the cybrids. Hybrids from parental nonenucleated cells were also isolated and analyzed for the expression of tumorigenicity. A reduction of the tumorigenic capacity in terms of tumor incidence and latency was clearly expressed in most of the cybrid clones studied. In the cybrids, saturation density and colony formation in agarose was also reduced. In most of the hybrid clones studied, a reduction was also observed in the tumorigenic capacity but not in saturation density or anchorage independence.