Analysis of erythropoiesis and serum Epo levels of Tfr2^BMKO mice. Mice were analyzed 4 months after transplantation with a WT (controls) or a Tfr2^−/− (Tfr2^BMKO) BM. Mice were fed as in legend to Figure 1 (see text for details). (A) Representative gating strategy for analysis of Ter119 subpopulations in controls and Tfr2^BMKO mice. Viable cells (impermeable to PI) from BM were analyzed for Ter119/CD44 expression. Ter119 were gated and further analyzed with respect to FSC and CD44 surface expression for subpopulation composition (gated cluster I-V). (B) The survival of erythroblasts in the BM was examined for annexin V binding to assess apoptosis. Representative histograms of annexin V binding in basophilic (gate cluster II), polychromatic (gate cluster III), orthochromatic erythroblast (gate cluster IV), and RBC (gate cluster V). Staining control is a sample in which PI and annexin V were omitted. (C) Histogram represents percentage of apoptotic cells in basophilic (gate cluster II), polychromatic erythroblasts (gate cluster III), orthochromatic erythroblast (gate cluster IV), and RBC (gate cluster V). (D) Serum Epo levels. Mean values of 3 to 9 animals for genotype and treatment (control IB, Tfr2^BMKO IB, control ID, Tfr2^BMKO ID) are graphed. Bars indicate standard error. Asterisks refer to a statistically significant difference. *P < .05.