Expression of Nix RNA during terminal erythroid differentiation. CD34⁺ cells harvested from the peripheral blood of healthy donors were cultured in the presence of EPO to induce terminal erythroid differentiation (“Materials and methods”) and were harvested on days 0, 2, 4, 6, 8, 10, 12, and 14 before RNA isolation and RT-PCR. (A) Equivalent amounts of cDNA were amplified with primers specific for the genes shown on the left. All PCR assays consisted of 30 cycles except GAPDH, which was amplified for 27 cycles, and Bcl-2, which was amplified for 33 cycles, because of low signals. (B) Expression patterns of Nix (black bars) and Bcl-xL (white bars) were confirmed using real-time quantitative RT-PCR (“Materials and methods”). Relative expression levels (±SD) shown are normalized to the levels of GAPDH mRNA detected on the same day.