Analysis of the ability of the hematopoietic microenvironment to support erythropoiesis. (A) A transplantation assay. Hematopoietic cells (10⁷ total BM cells/mouse) derived from donor mice (WT or kd/kd) were transplanted into lethally irradiated recipient mice (WT, kd/kd, or kd/kd::Tie-1-Cre, n = 3 for each group). Peripheral blood cells were measured for hematocrit levels (Hct), leukocyte numbers (WBC), and platelet numbers (PLT). **P < .01. NS indicates not significant. (B) The mRNA expression levels of HIF-2α in spleen (left panel) and BM (right panel) were examined in WT, kd/kd, and kd/kd::Tie-1-Cre mice by quantitative RT-PCR. The expression levels seen in WT were normalized to a value of 1 as the standard in each tissue (P < .01). NS indicates not significant. (C) Peripheral blood analysis (RBC, Hb, Hct, WBC, and PLT) was performed in WT, kd/kd, and kd/kd::Tie-1-Cre mice (*P < .05, **P < .01). Error bars represent SD. (D) Flow cytometric analysis of spleen cells prepared from WT and kd/kd::Tie-1-Cre mice. The numbers shown depict the frequency (%) of CD71⁺/TER119⁺ and CD71⁻/TER119⁺ cells.