Effects of activated Notch on HL-60 cell proliferation. Cells were plated at density of 0.1 × 10⁶/mL in RPMI supplemented with 10% FCS (A) and at density of 0.2 × 10⁶/mL in RPMI supplemented with 10% FCS and 1 μmol/L ATRA (B). Each day, cells were obtained, counted, and the percentage of GFP-positive cells determined by flow cytometry. Numbers express the mean of three experiments and represent the absolute number of HL-60 MSCV-GFP– and MSCV-ICN/GFP–positive cells/mL. Error bars represent standard deviation.