IRP1 deficiency leads to reticulocytosis and polycythemia. WT, IRP1^−/−, and IRP2^−/− mice (n = 7) were euthanized at the age of 4 to 6 weeks. (A) Peripheral blood smear stained for reticulocytes (indicated by arrows). (B) Fluorescence-activated cell sorter analysis of peripheral blood stained with thiazole orange. (C) Percentage of reticulocytes in peripheral blood. (D) Red blood cell (RBC) count. (E) Hemoglobin values. ***P < .001.