To evaluate the potential synergistic action of Celf2 loss and MLL-fusion in the leukemia-initiating event in AML development, we transduced hematopoietic progenitor cells from Celf2 KO and Celf2 WT mice with retrovirus expressing MA9 (Fig. S2A and Supplemental method). The gene discussed is CELF2; the disease is acute myeloid leukemia.