Increase in clonal variation in Chinese hamster ovary cells after treatment with mutagens.

Clonal variation has been studied in CHO cells. The variant phenotype was an altered morphology of clones in agar: the parental CHO cells give rise to solid clumps of cells (wild-type colonies); occasionally, dispersed colonies arise, and the cells display an invasive growth in agar (INGA-type colonies). The frequency of this altered phenotype can be enhanced by treatment with a variety of mutagens (EMS, ENU, 4NQO, N-Ac-AAF, ultraviolet light, and X-irradiation). Enhancement was not due to a selective killing of wild-type cells or to a side-effect of cytotoxicity, which suggests that DNA damage is the cause of the altered phenotype. The INGA-trait breeds true, but most of the isolated clones have an inherent instability.