Representative FACS analysis of hematopoietic tissues in Bex/Vex control and CBFβ-SMMHC/FLT3-ITD–reconstituted animals. (A) Bone marrow analysis of early B-lineage development. Cells were gated for Bex/Vex expression and then analyzed for B220 and CD19 expression. Bone marrow cells that lacked Bex/Vex expression were also analyzed from the same animals. (B) FACS analysis of thymocyte development was analyzed using CD4 and CD8 staining. (C) Bone marrow cells were stained with a cocktail of antibodies to antigens on mature blood cells (Lin⁻) and for c-Kit and Sca-1 expression using FACS. Absolute cell numbers of c-Kit⁺Lin⁻Sca-1⁺ (KLS) cells that were Bex⁺/Vex⁺ was determined from total bone marrow counts and the frequency of KLS cells within the indicated gates. Numbers on plots are percentages of total cells.