sCFU-E cells expansion is impaired in mice expressing truncated EpoR. (A) Diagrams of full-length EpoR and EpoR(core). (B) Epo-induced sCFU-E expansion is defective in EpoR(core) mice. Percentages of sCFU-E cells in the bone marrow or spleen were quantified at indicated times after Epo injection in mice expressing wild-type EpoR or EpoR(core). Statistically significant differences indicated on top of each bar are in comparison with time 0, whereas significant differences between EpoR and EpoR(core) at specific time points are specified. (C) Representative flow cytometry data from (B). (D) sCFU-E expansion after phlebotomy is defective in EpoR(core) mice. Statistically significant differences indicated on top of each bar are comparison with day 0, whereas significant differences between EpoR and EpoR(core) at specific time points are specified. (E) RBC counts after phlebotomy in mice expressing EpoR or EpoR(core) at indicated times. (F) RBC counts after PHZ-induced hemolysis in mice expressing EpoR or EpoR(core) at indicated times. (G) EpoR(core) mice die of erythropoietic stress elicited by PHZ treatment. Dosing of 62.5 mg/kg (PHZ^lo) or 87.5 mg/kg (PHZ^hi) is as indicated. (H) Sorted BFU-E and sCFU-E cells from EpoR(core) mice generated dramatically fewer erythroid progenies. Ter119⁺ erythroid progenies are enumerated at indicated time harvested from in vitro culture. Data represent the mean ± SD. ∗P < .05; ∗∗P < .01, 2-way ANOVA.