PU.1 regulates adult erythropoiesis. (A) Expansion of PU.1^+/G and WT BM erythroid progenitors cells in erythroid medium. A total of 105 WT or PU.1^+/G purified Lin^– (B220^–Gr1^–TER119^–CD3^–F4/80^–CD16/32^–NK1.1^–) BM cells were seeded in erythroid medium; cell numbers were counted daily. Graph is representative of 3 experiments, 5 mice of each genotype in all. (B) Erythrocyte regeneration following phenylhydrazine-induced stress. PU.1^+/G and WT mice were injected with phenylhydrazine (2 injections 24 hours apart) to induce anemia. The number of splenic CFU-E (top) and TER119⁺ cells (bottom) were quantified between 3 to 5 days after the first injection. Two experiments are shown (means and SDs), 3 mice for each time point.