Appearance of apoptotic cells in the cultures as measured by annexin V staining. CD34⁺ cells were grown with rhuMGDF in the absence or presence of 6 μmol/L PD98059 and stained with annexin V-FITC at the indicated days. The percentage of annexin V–positive cells was determined by FACS analysis. (A) Frequency of apoptotic cells in control cultures (▪) and cultures containing the inhibitor (▨). The results represent mean ± SD from 4 independent experiments. (B) Total number of apoptotic cells in the presence (▪) or absence (•) of PD98059. The results from a representative experiment are shown.