Cultured CD34⁺ cells express EPO and EPOR mRNAs. CD34⁺ cells prepared by magnetic sorting22 were cultured with EPO to preferentially favor differentiation of erythroid progenitors and precursors.30Aliquots of cells were taken at days 0, 2, 4, 6, 8, and 12; total RNA was isolated; and EPO and EPOR cDNAs were generated by RT-PCR by using specific primers. Size marker 123 bp ladder (M), negative control (−), genomic DNA (g), EPO cDNA (+) upper panel, EPO cDNA (+) lower panel.