Time course of expression of megakaryocyte or erythroid maturation-associated genes after treatment of UT-7/GM cells with EPO, TPO, or a combination with GM-CSF. UT-7/GM cells were cultured in tissue culture flasks with EPO (10 U/mL), EPO (10 U/mL) plus GM-CSF (10 ng/mL), TPO (100 ng/mL), and TPO (100 ng/mL) plus GM-CSF (10 ng/mL) for the times indicated. The cells were then harvested and prepared for isolation of total cellular RNA. The expression of γ-globin (A) and PF-4 (B) mRNAs was examined by Northern blotting. The membrane was rehybridized with ³²P-labeled human ribosomal DNA probe to show the amount of RNA loaded.