RUNX1 and leukemia: Figure 1d shows that the time point of RUNX1-ETO induction determined the outcome of differentiation. When cells were induced at day 0 and day 1, KIT expression was not affected (Supplementary Fig. 1c), CD41 was not upregulated and differentiation did not proceed further. Induction at day 0 of the expression of RUNX1-ETO9a, a splice variant of RUNX1-ETO which gives rise to a truncated protein that is capable of causing leukaemia in mice on its own20, resulted similarly in a defect in generation of CD41+ cells (Supplementary Fig. 2a,b).