PIT1-underexpressing mice displayex vivoerythroid maturation defects. Primary erythroid progenitors were isolated from BM of PIT1^+/+ and PIT1^neo/neo mice and cultured ex vivo for 4 days. (A-B) PIT1 (A) and EKLF (B) mRNA expression in primary erythroid progenitors. Results are normalized to day 0 for each genotype. (C) Percentage of benzidine-positive cells during ex vivo maturation. (D) β-globin mRNA expression in PIT1^neo/neo primary erythroid progenitors 2 days after ex vivo maturation induction compared with PIT1^+/+ cells. (E) Percentage of c-kit⁺ primary erythroid progenitors determined by FACS analysis. (F) Representative flow cytometric analysis of primary erythroid progenitors 3 days after ex vivo maturation induction. Percentages of labeled cells were calculated by taking into account the background labeling (baseline defined by omitting Ab). (G) p21 mRNA expression in primary erythroid progenitors during ex vivo maturation. Results are normalized to day 0 for each genotype. Data indicate the means ± SEM of at least 3 animals per genotype. Significant differences from PIT1^+/+ are indicated. *P < .05; **P < .01.