RUNX1 and acute myeloid leukemia: To this end, MSCVneo-MLL-AF9 + MSCV-PIG (as control) 40, MSCVneo-MLL-AF9 + MSCV-PIG-miR-550-1 (i.e., MLL-AF9 + miR-550-1), MSCVneo-MLL-AF9 + MSCV-PIG-miR-550-1 mutant (i.e., MLL-AF9 + miR-550-1 mut), MSCVneo-AE9a (AML1-ETO9a fusion gene; a truncated AML1-ETO fusion gene causing rapid AML onset in mice 41) + MSCV-PIG (as control), MSCVneo-AE9a + MSCV-PIG-miR-550-1 (i.e., AE9a + miR-550-1) or MSCVneo-AE9a + MSCV-PIG-miR-550-1 mutant (i.e., AE9a + miR-550-1 mut) were separately co-transduced into normal murine BM progenitor cells prior to replating on methylcellulose medium.