Cellular differentiation and neoplasia: characterization of subpopulations of cells that have neoplasia-related growth properties in Syrian hamster embryo cell cultures.

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Abstract
Cellular subpopulations having 2 of the growth properties of neoplastically transformed cells (lack of postconfluence inhibition of cell division (CI-) and anchorage independence of growth (AD-)) were found in cell cultures established from 10- to 13-day-old Syrian hamster embryos. The subpopulations having these properties decrease with the increasing gestation period of the embryo as well as with continuing passage in vitro. The decrease in these subpopulations was also observed when they were cultured on a lethally irradiated confluent monolayer of contact-inhibited cells (cell mat), a selection condition for CI- cells. Negative selection cannot be the explanation for the loss of CI- cells in the population, leaving 2 other possibilities: the loss of proliferative capacity of the CI- cells or the acquisition of sensitivity to postconfluence inhibition of cell division (CI+) of this subpopulation on in vitro culture or in vivo growth. The CI- subpopulations were isolated clonally from cell mats and cultured continuously on cell mats or plastic dishes. These cells apparently did not lose proliferative capacity but acquired the contact-inhibited phenotype. Since embryonic development in vivo also decreases CI-/AD- subpopulations, the disappearance of these subpopulations may be due to cellular differentiation of the CI-/AD- cells to become CT+/AD+ cells.