The presence of Dll4Fc during the 5 first days of cultures is sufficient to inhibit terminal MK differentiation. Human cord blood CD34⁺ cells were plated onto control or Dll4Fc-coated wells in the presence of huTPO and huSCF. At day 5, cells were plated onto freshly prepared control or Dll4Fc-coated wells. At day 10, sorted CD41a⁺CD42b⁺ cells were plated onto control or Dll4Fc-coated wells in the presence of huTPO, and the % of platelet-forming cells was evaluated 4 days later. (A) Histogram representation of the % of CD41a⁺CD42b⁺ cells after 10 days of culture. Mean ± SEM from 3 independent experiments. Black bars represent culture period performed in the presence of Dll4Fc, while white bars represent culture period without Dll4Fc. (B) Histogram representation of phase-contrast microscopy analyses of the % of platelet-forming cells among sorted CD41a⁺CD42b⁺ cells (mean ± SEM from 3 independent experiments).