Normal differentiation kinetics of E2f4^–/– fetal liver erythroid cells in vitro. FL erythroid cells pooled from E2f4^+/+ and E2f4^–/– E12.5 embryos were expanded and induced to differentiate in vitro. Features of differentiation were measured at 0, 12, 24, 48, and 72 hours following differentiation induction. (A) Morphologic analysis of cytospins following erythroid differentiation by May-Grunwald-Giemsa and benzidine (dark brown) staining. (B) Average cell size (fL) determined by Coulter counter analysis. (C) Proportion of cells expressing hematopoietic markers c-kit (circles) and Ter119 (triangles) by FACS. (D) Relative abundance of mRNA transcript of erythroid differentiation marker β-globin compared with β 2M, assessed by real-time PCR; E2f4^+/+, ▪; E2f4^–/–, ##. For all other graphs, E2f4^+/+, closed symbols; E2f4^–/–, open symbols. Error bars indicate standard deviation.