Runx factors mediate PU.1 transcription in HSCs through binding sites at the −14kb URE. (A) mRNA levels of indicated Runx genes in unselected whole bone marrow (BM) cells and isolated SLAM⁺ LSK cells (HSC-enriched population). Shown are average levels + standard deviation (SD); n = 7 (B) mRNA levels of indicated Runx genes after CRE-induced Runx1 deletion in SLAM⁺ LSK cells. Shown are average levels ± SD. n = 4; *P < .05. (C) Simplified scheme of murine PU.1 locus indicating the 3 Runx binding sites, all of which have been selectively mutated from TGTGGTA to TGACCTA in the knockin mouse model PU.1-URE-mRunx. (D) PU.1 mRNA levels in SLAM⁺ LSK cells of PU.1-URE-mRunx and Runx1-deleted mice compared with control. Shown are average levels ± SD. n = 4; *P < .05.