Orthochromatic erythroblasts in the E13.5 Eklf^−/− fetal liver have increased proportion of cells in S phase compared with Eklf^+/− and Eklf^+/+ fetal livers. (A) E13.5 Eklf^+/+ and Eklf^−/− fetal livers retrieved 1 hour after BrdU injection of pregnant mice were stained for BrdU, CD71, Kit, and DNA (DAPI) and analyzed by imaging flow cytometry. Representative images of Eklf^+/+ and Eklf^−/− BrdU positive and BrdU negative orthochromatic erythroblasts are shown. See supplemental Figure 3 for images of other maturing erythroblasts. (B) Gating of Eklf^+/+ and Eklf^−/− BrdU positive (S phase) orthochromatic erythroblasts by imaging flow cytometry is shown. See supplemental Figure 3 for cell cycle analysis of other maturing erythroblasts. (C) Quantitation of percentage of Eklf^+/+, Eklf^+/−, and Eklf^−/− BrdU positive (S phase) cells during progressive stages of erythropoiesis, as analyzed by imaging flow cytometry. Eklf^+/+ and Eklf^+/− fetal livers (n = 5); Eklf^−/− fetal livers (n = 2). **P < .001.