Runx2 expression in BM hematopoietic progenitor cells. (A) Representation of Runx2 gene (top), showing the alternative transcription initiation sites (arrows) from distal promoter (P1) at exon 1 and proximal promoter (P2) at exon 2, with coding exons (gray box) and untranslated sequences (white box). The major Runx2 transcript isoforms from each promoter and the alternative spliced exon 5 are depicted in black boxes (bottom). (B) RELs of Runx2 isoforms (left) in sorted HSCs (), CMP (□), GMP (■), and MEP () cells by quantitative PCR. Transcripts for total Runx2 (Rx2), P1- or P2-specific, and exon 5-containing (Ex5) isoforms. (C) Relative expression levels of Runx2 (Rx2) and Runx1 (Rx1) in sorted HSCs, CMP, GMP, and MEP cells determined by quantitative PCR and normalized to primer bias using limiting dilution correlation curve. (D) Experimental design of in vitro myeloid differentiation assay and serial replating of wild-type (wt) and Cbfb-MYH11-expressing (CM) BM cells infected with empty (MIG) or Runx2-expressing (Runx2) retrovirus; 10⁴ GFP sorted cells were cultured in methylcellulose. (E) Representative photograph of day 7 CFUs comparing wild-type (top) and Cbfb-MYH11-expressing (bottom) BM cells infected with empty (MIG) or Runx2-expressing (Runx2) retrovirus in plating 1. (F) Histogram showing the number of day 7 myeloid CFU in platings 1 (), 2 (■), and 3 (□). Data are mean plus or minus SD from at least 2 independent experiments, each in triplicate.