Parallel reduction in the frequencies of CFU-E colonies and EPs in mice lacking the transcription factor ICSBP. Lin^–Sca-1^–IL-7Rα^– cells from ICSBP^+/+ (A) and from ICSBP^–/– (E) mice were analyzed for expression of c-Kit and IL-3Rα. C-Kit⁺IL-3Rα^– cells were further separated by staining for CD71 versus CD41 (B,F). Frequencies of EPs were strongly reduced in ICSBP^–/– (G) compared to ICSBP^+/+ (C) BM. This decline in the EP frequencies parallels the reduction in the CFU-E frequencies in total BM from ICSBP^–/– (H) compared to ICSBP^+/+ mice (D). Numbers in panels A, B, E, and F are relative percentages of the populations in the indicated regions. Data in shown panels C, D, G, and H are mean numbers from duplicate CFU-E cultures for each experiment (Exp.).