[clonal analysis of the independence of tumor cell multiplication from the substrate]

The clone of near-diploid mouse transformed CAK-25AGr cells is characterized by the stable cloning efficiency in a semi-solid medium (about 10(-5) per cell plated in methylcellulose). It was shown that colonies in the semi-solid medium were formed by rare single cells and did not arise as a result of slow multiplication of all cells in the population. These cells are not genetical variants different from other cells in the culture. This is assumed on the basis of following data. First, the majority of the subclones arising in methylcellulose (9 of 12) retained parental cloning efficiency in the semi-solid medium. Second, all 6 subclones picked from the solid substratum had the ability to form colonies in methylcellulose with the frequency not lower than that of the parental clone. Apparently, the proliferation in methylcellulose of the transformed cells studied is a stochastic process. Each cell in the culture has the ability to initiate a colony in the semi-solid medium with the certain probability. This probability is a heritable characteristic of the cloned cell line. It is possible that this characteristic reflects the norm of reaction of the cells to some environmental factors.