E13.5 Eklf^−/− erythroblasts can undergo terminal differentiation reaching the orthochromatic erythroblast stage but do not enucleate. (A) Schematic of the stages of terminal differentiation of E13.5 fetal liver erythroid cells showing the expression profile of Kit, CD71, and Ter119 cell surface markers. During terminal differentiation, erythroid precursors express both CD71 and Ter119. (B) Profile of total intensity of CD71 and Ter119 staining analyzed by imaging flow cytometry of E13.5 Eklf^+/+, Eklf^+/−, and Eklf^−/− fetal liver cells. In Eklf^+/+ and Eklf^+/− livers, populations of erythroid cells (CD71+) progress from Ter119lo to Ter119+ as they mature. In Eklf^−/− livers, the CD71+ cells, although present, lack Ter119 expression. (C) MGG staining of cytospins from E13.5 fetal liver cells show that although Eklf^+/+ and ^+/− fetal livers contain enucleated definitive erythroid cells (red arrows), Eklf^−/− fetal livers do not. In addition, Eklf^−/− fetal livers contain orthochromatic erythroblast cells (green arrows) similar to Eklf^+/+ and Eklf^+/− fetal livers. Scale bars correspond to 50 µm length. Original magnification ×40. Slides were processed at the same time. (D) Quantification of percentage of enucleated cells from cytospins of E13.5 Eklf^+/+ (n = 34 fields; a total of 1237 cells), Eklf^+/− (n = 12 fields; a total of 530 cells), and Eklf^−/− (n = 85 fields; a total of 2805 cells) fetal livers. ***P < .001.