Evolution of erythroid (Ery), megakaryocytic (MK), and GM clonogenic progenitors in MGDF-induced cultures. Clonogenic progenitors in cultures performed in the absence or the presence of 6 μmol/L PD98059 were quantified at the indicated days by semisolid culture assays as described in Materials and Methods. (A) Total number of colonies formed with control (▪) or PD98059-treated cultures (▨). The results from a representative experiment, where determinations were done in duplicate, are shown. (B) Percent of increase in relative (▩) or total (□) colony numbers obtained with PD98059-treated cells as compared with control cells. Results are mean ± SD of at least 4 independent experiments for each type of colony.