Fetal liver cells underexpressing PIT1 display erythroid maturation defects. Primary erythroid progenitors were isolated from fetal livers of PIT1^+/+ and PIT1^neo/Δ5 mice and cultured ex vivo during 4 days. (A) 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). (B) Percentage of cells that were TER119⁺/CD71⁻. Data indicate the means ± SEM of at least 3 independent experiments. Significant differences from PIT1^+/+ are indicated. *P < .05; **P < .01. (C) May Grünwald-Giemsa stained cytospin of ex vivo cultured erythroid progenitor cells isolated from fetal livers of PIT1^+/+ and PIT1^neo/Δ5 mice at day 0 (D0) and day 3 (D3). Bar indicates 100μm at a 40× magnification. (D) Percentage of cells that were CD71⁺/annexin V⁺, and (E) TER119⁺/annexin V⁺ during fetal liver cell ex vivo maturation induction. Data indicate the means ± SEM of at least 3 independent experiments. Significant differences from PIT1^+/+ are indicated. *P < .05. (F-G) Percentage of fetal liver cells that were CD71⁺/BrdU⁺ (F) and TER119⁺/BrdU⁺ (G). Cells were cultured with 10μM BrdU for 2 hours and then analyzed 6-14 hours after pulse. Data indicate the means ± SEM of at least 3 independent experiments. Significant differences from PIT1^+/+ are indicated. *P < .05; **P < .01.