Expression of Id2 is upregulated in CFU-E and proerythroblast stages. (A) Dynamic changes of EYFP expression levels during the development of erythroid progenitors. BMCs expressing EYFP under control of the Id2 promoter (Id2-EYFP) were evaluated for CD71 and Ter119 expression by flow cytometry (middle). The expression of Id2-EYFP was evaluated in CD71⁺/Ter119^−/lo CFU-E/proerythroblasts (upper left) in CD71⁺/Ter119⁺ basophilic erythroblasts (upper right) and in /CD71⁻/Ter119⁺ chromatophilic/orthochromatophilic erythroblasts (lower right). Id2-EYFP mice (black line) cells and control mice (gray line) for each histogram are compared. (B) Bar graph represents the percentage of Id2-EYFP–positive cells ± SD found in each stage of erythroid progenitor development from 3 mice. The data are representative of 3 independent experiments.