Lengthening of the G1 phase is not strictly correlated with differentiation in Friend erythroleukemia cells

Friend murine erythroleukemia cells (Friend cells) undergo erythroid differentiation in vitro with an increased probability when cells are cultured in the presence of dimethyl sulfoxide (Me₂SO) or other agents. Exponentially growing Friend cells, after dilution into medium containing Me₂SO, underwent a transient lengthening of the G1 phase of the cell cycle before they became committed to erythroid differentiation. For nine inducing agents, a positive correlation was found between the percentage of cells that had differentiated and synthesized heme, and the percentage of progenitor cells in which a lengthened G1 phase had previously been observed. This correlation was not found, however, with two other potent inducing agents, hypoxanthine and actinomycin D. Moreover, cells that underwent a lengthened G1 phase did not always terminally differentiate. One such example was a Me₂SO-resistant, variant Friend cell line (520a) grown in the presence of Me₂SO. These results imply that the prolonged G1 phase, although observed with many inducers, is not a prerequisite for erythroid differentiation with all inducers.