Influence of Rs12041331 on MK progenitor proliferation and PEAR1 expression during MK differentiation. (A) Left panel: histogram for CD41a and PEAR1 during differentiation of CD34⁺ cells from day 0 to day 14, as indicated. Right panel: CD34, CD41a, and PEAR1 expression measured by FACS analysis and expressed as mean fluorescence intensity during differentiation of CD34⁺ cells into MK precursors harvested at day 0 (D0), day 7 (D7), and day 14 (D14). (B) Left panel: Number of CFU-MK, defined as small (3-20 cells), medium (20-80 cells), and large (>80 cells) colonies, counted in a blinded fashion at day 8 after differentiation in GG (n = 3) vs AG+AA (n = 3) individuals. *P < .05, multiple unpaired Student t test with post-Holm-Sidak for multiple comparisons. Right panel: GG (n = 2) vs AG+AA (n = 3) PEAR1/CD41a ratios measured on CD41a-positive events at day 7 of differentiation. SP1, SP2, SP3 are CD41a-positive subpopulations defined by marker positivity and size (Forward Scatter, FSC) as defined in supplemental Figure 4. Comp-FITC-A, comparative mean fluorescene intensity for FITC-labeled antibody against CD41a; Comp-PE-A, comparative mean fluorescence intensity for PE-labeled antibody against PEAR1.