Altered marrow response to exogenous erythropoietin in HDAC5^−/− mice. (A) Hematocrit (HCT) and RBC in adult WT and HDAC5^−/− animals receiving weekly injections of the long-acting agent darbepoetin alfa. N = 6 animals/group. (B) Erythroid maturation in marrows of WT and HDAC5^−/− mice after either no treatment (basal) or 3 injections of darbepoetin alfa (Epo). Flow cytometry for expression of CD71 and Ter119, with percentages shown within indicated quadrants. (C) Comparison of percentages of the less mature Ter119⁺ CD71⁺ progenitors and of the more mature Ter119⁺ CD71⁻ progenitors. Composite of data from panel B analyzing marrows from WT or HDAC5^−/− (KO) mice either untreated (basal) or darbepoetin-treated (mean ± SEM; n = 3/group).