Levels of expression of TfR1 andTfR2 mRNA during erythroid cell differentiation.

Human erythroid cell populations at different stages of differentiation were analyzed by real-time Q-PCR. Bars show mean ± SD. (A) Levels of TfR1 and TfR2 mRNA were analyzed. CD34⁺/d4 represents human erythroid cells positively selected for CD34 expression after 4 days in culture. GPA⁺/d4 and GPA⁺/d10 represent human erythroid cells positively selected for glycophorin A expression at day 4 and day 10 of culture, respectively. In all these experiments, the cells were cultured in the presence of erythropoietin. (B) Levels ofTfR2-α transcripts were analyzed by means of α-form–specific primers. The CD34⁺/d4 erythroid progenitors were cultured in the presence of erythropoietin and harvested on different days of culture. The purity and homogeneity of these populations were confirmed by flow-cytometric analysis, and the phenotypes of each population are shown in each panel. The absolute values (attomoles per microgram) of expression shown in panels A and B are not directly comparable, since the cells used in these experiments were from different donors.