RBM38 is required for terminal erythropoiesis. (A) RBM38 knockdown in ex vivo–differentiated erythroblasts. (B) RBM38 inhibition blocks proliferation during terminal erythroid differentiation. Growth curves show the number of live ex vivo–TER119⁺ CD71⁺ erythroblasts differentiated erythroid cells treated with Rbm38-targeting or non-targeting shRNAs. (C) RBM38-depleted cells accumulate in the G1 cell cycle phase. Plots show the results of DNA staining with propidium iodide (PI) and with a thymidine analog (EdU) in shRNA-transduced cells. The proportion of cells at each cell cycle phase is shown in the bar graph at the right. (D) Elevated apoptosis of RBM38-depleted cells after 24 hours of ex vivo differentiation. Plots display DNA content (PI staining) versus apoptotic status (annexin-V staining) of shRNA-transduced cells. Apoptotic cell fractions are shown in the bar graph at the right. (E) RBM38 inhibition impairs red cell enucleation. Plots display the level of the differentiation surface marker TER119 (fluorescent immunolabeling) versus DNA content (Hoechst staining) of shRNA-transduced live cells after 48 hours of ex vivo culture. Gates mark enucleated reticulocytes. Relative enucleation efficiencies are shown in the bar graph at the right. *P < .05, Student t test.