Membrane-bound Dll4 and Dll1 repress MK differentiation from CD34⁺ cells. (A) Human cord blood CD34⁺ cells were cultured for 10 days onto control OP9-GFP or OP9-huDll1 or OP9-huDll4 stroma in the presence of huSCF and huTPO before flow cytometric analyses (1 representative experiment). (D) Histogram representation of the % of CD41a⁺CD42b⁺ cells at day 10 of the culture. Mean ± SEM from 3 independent experiments.