Erythropoiesis in TfR2^−/− mice. (A) CFU-E assay of TfR2^−/− and wild-type mice. Bone marrow cells (2 × 10⁵) from the femurs and tibias of 2 TfR2^−/− and 2 wild-type mice at 4 weeks of age were cultured in methylcellulose medium dedicated to CFU-E growth (Methocult M3234, StemCell Technologies) supplemented by the indicated Epo concentrations. Colonies were scored after 48 hours of culture. The results are representative of 2 independent experiments performed in duplicate. (B) Hematological values from TfR2^−/− and wild-type littermates at 4 weeks of age. HCT, hematocrit; HGB, hemoglobin; RBC, red blood cells; Retic, reticulocytes; MCV, mean cell volume; MCH, mean cell hemoglobin. (n = 6 for both TfR2^−/− mice and wild-type mice; values are the mean ± SD). (C) Epo concentrations in the serum of TfR2^−/− (n = 4), sibling pairs of wild-type (n = 3) and liver-targeted deletion of TfR2 (TfR2 LCKO, n = 4) mice were determined by sandwich ELISA (R&D Systems). Student t test: P < .01 between TfR2^−/− and wild-type mice and between TfR2^−/− and LCKO mice, P > .15 (NS) between wild-type and LCKO mice.