Expression of C/EBPα-ER in primary human CD34⁺ cells.

(A) The retroviral vector MIGR1 is shown schematically. The rat C/EBPα cDNA fused in-frame with the ligand-binding domain of the estrogen receptor (C/EBPα-ER) was cloned into the EcoRI restriction site of MIGR1. (B) Western blot analysis of human CD34⁺ cells transduced with MIGR1 or MIGR1 C/EBPα-ER using an α-C/EBPα antibody (lanes 1-2). Expression of C/EBPα-ER in the producer cell line RD18 was used as a positive control (lane 3). (Note that the 45-kDa band shown in lanes 2 and 3 is not present in lane 1 and likely represents a degradation product of the ER fusion protein.) (C) The experimental design to evaluate the effects of C/EBPα on human hematopoietic progenitor cell behavior and to identify C/EBPα target genes is shown schematically (IFA indicates immunofluorescence assay).