RUNX1 directly controls transcription of integrin β3 (CD61) in the HE. (A) (Left) RPKM mapped reads expression values of CD61, CD41, and CD51 genes in Runx1^wt and Runx1^ko HE. (Right) Fold change of RPKM values of CD61, CD41, and CD51 genes in Runx1^wt HE normalized against Runx1^ko. *P < .05. (B) qPCR for CD61 mRNA expression levels in non-HE (cKIT⁻, TIE2⁻, CD41⁻,CD45⁻, and TER119⁻) and HE (cKIT⁺, TIE2⁺, CD41⁻, CD45⁻, and TER119⁻) enriched populations sorted from E7.5 and E8.5 heterozygous (HET) (RUNX1^RFPp/+) and KO (RUNX1^RFPp/RFPp) embryos. Data are normalized against the HET HE population. (C) Luciferase assay with the full length and truncated +16 kb CD61 cis-regulatory element cloned upstream of the CD61 promoter. The “2R” depicts the 2 active RUNX1 binding motifs. The activity of all luciferase vectors was tested in iRunx1^Runx1−/− HE 24 hours postdox induction. Values were normalized against “no dox” treatment. *P < .05. (D) cKIT/TIE2 and CD61/CD41 FACS plots of iRunx1^Runx1−/− HE cells in the presence or absence of dox. HP, hematopoietic progenitors.