Epcr expression on murine LSK cells is stabilized by Thpo/Mpl signaling in vitro and in vivo. (A) Epcr expression of in vitro cultured wt LSK cells in medium supplemented with 20 ng/mL Scf or 10 ng/mL Scf/100 ng/mL Thpo 20, 36, and 60 hours after isolation and culture time. (B-D) Epcr expression of in vitro–cultured wt LSK cells in medium supplemented with 20 ng/mL Scf and 20 ng/ml Flt3-L (-Thpo) or 20 ng/mL Scf, 20 ng/mL Flt3-L, and 100 ng/mL Thpo (+Thpo) 36 and 60 hours after isolation and culture time (3 independent LSK sorts). Based on the median Epcr intensity, the fold change of Epcr intensity was calculated. Thpo stimulation of LSK cells maintained Epcr expression at both time points (P = .031; Wilcoxon test; paired analysis; comparing the Thpo⁺ vs Thpo⁻ cultures). (E) Total BM of wt (n = 3) and Thpo^−/− (n = 3) mice was stained for LSK and analyzed for the expression of Epcr and Mpl. The bars summarize the Epcr expression on the Mpl⁺ population of the LSK cells. In the absence of Thpo, there is no positive correlation of Epcr and Mpl. MFI, median fluorescence intensity.