Erythropoietin induces PlGF expression in bone marrow progenitor cells. CD34⁺ progenitor cells from a normal bone marrow were analyzed for PlGF mRNA by RT-PCR analyses soon after isolation (lane 1) or after a 12-hour exposure either to 3 U/mL erythropoietin (lane 2) or to erythropoietin-independent erythroid differentiation medium (IL-6, sIL-6 receptor, and SCF; lane 3) or erythropoietin-independent erythroid differentiation medium with additional erythropoietin (3 U/mL; lane 4). The bottom panel shows an RT-PCR for β-actin for the corresponding samples. Lanes 5 and 6 consist of negative (H₂O) and positive controls (human pulmonary microvascular endothelial cells), respectively.