Reversible changes in the EPO-induced erythroid differentiation. UT-7/GM cells (lanes 1 and 7) were exposed to EPO (10 U/mL) for 4 weeks (lanes 2 and 8) and sequentially cultured with GM-CSF (10 ng/mL) alone for 1 week (lane 3) or 2 weeks (lanes 4 and 9). Then, the cells were obtained and prepared for the detection of hemoglobin synthesis, and the rest were sequentially cultured with EPO (10 U/mL) alone for 1 week (lane 5) or 2 weeks (lanes 6 and 10) and harvested. (A) Dianisidine-staining. (B) Northern blot analysis of γ-globin gene. The membrane was rehybridized with ³²P-labeled β-actin cDNA probe to show the amount of RNA loaded.