Enhanced ex vivo maturation of HDAC5^−/− progenitors in the presence and absence of erythropoietin. (A) HDAC5^−/− progenitors yield increased proportions of Ter119⁺ CD71^Intermediate cells (R5) in erythropoietin-containing cultures. Sorted Ter119⁻ CD71^Bright progenitors from WT and HDAC5^−/− adult marrows were cultured 3 days in G1ER maintenance medium with 2 U/mL erythropoietin. Flow cytometric plots show proportions of cells at indicated stages (R2-R5) of erythroid maturation, with gating on viable cells. (B) Composite of 3 experiments performed as in panel A comparing WT and HDAC5^−/− (KO) progenitors (mean ± SEM). (C) Erythropoietin–independent erythroid maturation of HDAC5^−/− progenitors. Flow cytometric plots from an experiment conducted as in panel A, except using medium lacking erythropoietin (gating on viable cells). (D) Composite of 3 experiments conducted as in panel C, showing percentage Ter119⁺ cells (mean ± SEM).