Stimulation of DNA synthesis in cultures of mouse embryo fibroblast‐like cells

Abstract

Abstract Stimulation of the DNA synthesis and mitoses in stationary cultures of mouse embryo fibroblast‐like cells was induced by various agents such as ribonuclease, digitonin, fresh medium and commercial preparations of hyaluronidases. Time sequence of stimulation was similar in experiments with all these agents. Cells were activated to enter S phase from GI phase. The rise of the number of DNA‐synthesizing cells was preceded by a latent period of about 8–12 hours with the maximal number of DNA‐synthesizing cells being observed at 16–24 hours. Mitotic wave was observed after the wave of DNA synthesis. Stimulation of DNA synthesis and mitosis was not preceded by any significant decrease of an average cell density in the culture. The progeny of activated cells had no greater chance than other cells to be activated again when stimulation was repeated. It is concluded that similar proliferative reactions can be induced in stationary cultures by a variety of diverse agents. Possible role of cell surface changes in the induction of these reactions is discussed.