The MEP compartment is reduced in the absence of Gfi-1B. (A-B) Erythroid and megakaryocytic colony formation in semisolid medium. At 48 hours after retroviral infection, before induction of erythroid differentiation (E0), infected CD34⁺GFP⁺ cell populations were plated in Methocult in the presence of EPO, IL-3, IL-6, and SCF (A) or in Megacult in the presence of TPO, IL-6, and IL-3 (B). Results are from 6 independent experiments and are mean ± SD. **P < .001. (C) Comparison of the size of the 3 progenitor populations from shControl- or shGfi-1B–infected cells. CD38⁺CD34⁺GFP⁺ cells were separated according to their CD123 and CD45RA expression. Percentage of cells in the 3 populations was indicated in the gates. Results are representative of 3 independent experiments. (D-E) Colony readout of sorted cells from transduced cells (gates described in panel C) in Methocult (D) or in Megacult (E). Results are representative of 3 independent experiments. (F) Gfi-1B and Gfi-1 expression in CD34⁺, CMP, GMP, and MEP populations. Total nuclear extracts were prepared from cells of each population and analyzed by immunobloting using antibodies recognizing Gfi-1B, Gfi-1, and β-actin (as control to confirm equal protein loading).