Abstract There is no cell proliferation in very sparcely plated chick embryo cell cultures. Substituting conditioned medium or adding of ethanol‐fixed homologous cells to the cultures accelerates cell colony growth. The mechanism for the mitogenic action of fixed cells is considered to be the contact stimulation of cell proliferation, and addition of extra cells to sparse culture is believed to mimic the cell micro‐environment existing in subconfluent cultures. The role of diverse cell—cell contacts in cultured cell growth regulation is discussed. The procedure used (addition of ethanol‐fixed cells) may improve normal cell cloning techniques.
The conditions of the cultivation of chick embryo diploid cells were alternated (prolonged maintenance with or without medium replacement, with or without consequent cell replating in fresh medium). In different times of culture growth, the cell DNA content was assessed by cytophotometry; the percentage of non-labeled mitoses after incubating the cells with 3H-thymidine and colcemide, as well as the cell density were determined. The phenomenon, detected earlier, of the accumulation of cells containing 4c DNA during the transition of the culture from logarithmic into the stationary phase of growth, was confirmed. These cells were shown to differ in their ability to survive in conditions of stationary culture and by proliferative potential. The fraction of cells reversibly arrested in G2-period was described, by which fraction the change of the cell population size is occurring after the decrease of its proliferation rate. The transitional stage is distinguished at the beginning of the stationary phase of culture growth. During this stage the stabilization of structural and numerical composition of the population is taking place.
In sparsely seeded (1.10(3) cells/sm2) chick embryo cell cultures no cell proliferation commonly occurs. However, such factors as increasing cell density, a conditioned medium, or addition of ethanol fixed homologous cells to the culture may accelerate the cell growth. The mitogenic action of fixed cells serves as a contact stimulation of cell proliferation (Gasparian, Grigorian, 1989, 1990). Distant and contact cell-to cell interactions, that involve soluble and insoluble cell derived mitogens, are supposed to operate during the log phase of culture growth. The addition of an excess of cells to the previously sparse culture may mimic the cell microenvironment commonly existing in subconfluent cultures. The role of diverse cell-to cell contacts in the cell growth regulation is discussed. The addition of ethanol-fixed cells may improve the cell cloning technique.
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