Expression of CHOP during granulocytic differentiation of normal human CD34⁺ cells. CD34⁺ cells isolated from normal human bone marrow were cultured with media supplemented with stem cell factor (50 ng/mL) and PIXY321 (20 ng/mL). Cells were harvested for total RNA at the indicated days. Expression of CHOP and GAPDH (internal control) mRNA was examined by semiquantitative RT-PCR. All PCR products were electrophoresed on a 1.5% agarose gel and were transferred to a nylon membrane by alkaline transfer. Hybridization of the membranes was performed using γ-³²P-ATP end-labeled internal oligonucleotide probes to confirm specificity of the PCR product. The entire experiment was repeated 3 times using RNA samples isolated independently from separate cultures. Ethidium bromide staining of the agarose gel of RT-PCR reactions for expression of CD34 and CD11b are shown here as differentiation controls (as they were in previously published work by Park et al²² ).