Deficiency in an Mk-biased CD42a⁺ subpopulation in RUNX-1^+/− iHPCs. (A) Megakaryopoiesis in a human iPSC system highlighting generation of iHPCs and iMks. On day 7 after exposure of adherent iPSCs to a directed differentiation protocol, free-floating, multipotent CD235a⁺CD41⁺ iHPCs emerged that included CD42a⁻ and CD42a⁺ iHPC subpopulations. (B) Flow cytometric analysis of day 7 iHPCs showing the CD42a⁺ iHPC subpopulation that is present at similar frequencies in all control lines, but is severely reduced in all RUNX-1^+/− lines. (C) Quantitation of panel B, showing the mean number of CD42⁺ iHPCs detected and normalized per well for iPSCs seeded ±1 SEM (n = 5-15 experiments per study arm). (D) Colony-forming assays of L1-C vs L1 iHPCs, showing quantitation of the mean number of Mk, erythroid, and granulocyte/macrophage (GM) colonies, normalized to the number of day 7 iHPCs seeded ±1 SEM (n = 4 experiments per study arm). (E) Same as panel D, but for large Mk colonies (>20 Mks/colony). All P values were determined by Student t test.