Runx1-IRES-GFP KI mice lack the expression of 3 Runx1 isoforms. (A) Structure of the Runx1-IRES-GFP KI construct. Boxes with numbers represent exons. Light gray boxes are RHD, and dark gray boxes are regulatory domains. Arrowheads show the positions of primers (F, R1, and R2) used for panel B. (B) Expression of Runx1 isoforms in total BM cells by RT-PCR. KI cells lack Runx1b/cEx6⁻ and Runx1bEx6e. GAPDH serves as a loading control. Water lane is the negative control. Representative result of 3 independent experiments is shown. (C) Protein expression of Runx1 in lineage-depleted c-Kit–enriched BM cells. KI lane has the same level of the major band although it lacks smaller bands which correspond to Runx1b/cEx6⁻. Runx1bEx6e band is undetectable in either WT or KI lane. α-Tubulin serves as a loading control. Representative result of 2 independent experiments is shown. Neo, neomycin resistance gene; PolyA, polyadenylation signal.