Erythroid differentiation arrest in ERG/GATA1s mice. (A) Schematic representation of erythroid differentiation indicating early erythrocytes as Ter119⁺/CD71⁺ and late differentiated erythrocytes as Ter119⁺/CD71⁻. (B) Increase in early erythroblast population compared with late differentiated erythrocytes in ERG/Gata1s males. FL cells were isolated from E14.5 Wild-type, TgERG, Wt/Gata1s, and ERG/Gata1s male embryos and stained with Ter119 and CD71. Statistical significance between Wt embryos and the remaining genotypes was measured using the t test. (C-D) Reduced benzidine-stained cells in ERG/Gata1s males. Representative images of benzidine-stained FL cells (C) and a graph averaging the ratio of benzidine-positive cells in FLs isolated from E14.5 Wt, TgERG, Wt/Gata1s, and ERG/Gata1s male and female embryos (D). The bar graph represents the average of at least 3 experiments. (E) Giemsa stain of cytospins of E14.5 FL cells show a decrease in maturing erythroblasts and increase in immature proerythroblasts in ERG/Gata1s males compared with Wt/Gata1s males. (F) Expression of hemoglobin. Adult hemoglobin β major chain (Hbb-b1) expression was measured by real-time PCR in E14.5 FL cells from Wt, TgERG, Wt/Gata1s, and ERG/Gata1s males. *Significant difference from Wt hemoglobin expression was measured using the t test (P = .00037 for TgERG; P < .000001 for Wt/Gata1s; and P < .00001 for ERG/Gata1s).