Effects of activated Notch1 on cell cycle distribution during HL-60 cell differentiation. Transduced HL-60 induced to differentiate in presence of ATRA were analyzed every 24 hours for DNA content and CD11b expression. Cells were harvested, labeled with anti-CD11b-PE MoAb and than stained with the DNA dye TOPRO-3 as described. Top panel: contour plots represent fluorescence intensity for CD11b on the x-axis and for GFP on the y-axis; gates show the populations, GFP-positive and CD11b-negative, selected for DNA analysis. Central panel: cell cycle distribution analyzed on gated populations at 48 and 72 hours after ATRA treatment. Bottom panel: values represent the average of 10 independent observations at days 2, 3, and 4 of ATRA treatment and express the percentage of cells in G₀/G₁, S-phase and G₂/M analyzed as described above.