siRNA to caspase-3 is effective in reducing caspase-3 activity and in blocking erythroid differentiation. (A) The relation of the 2 caspase-3 siRNAs to the sequence of the mRNA and protein-coding region of caspase-3. (B) CD34⁺ progenitor cells were electroporated with siRNA-1 or -2 or a control siRNA at day 0 and then assayed over time for caspase-3 enzymatic activity. Differences between control and siRNA-treated cultures were evaluated by t test. ^*P < .01; +P < .05. Error bars indicate SD. (C) Cell lysates were immunoblotted for protein levels of caspase-3, acinus and, as a control, GAPDH using control and caspase-3 siRNA-1-treated cells. Arrows indicate bands corresponding to procaspase-3 (P) and the cleaved 17-kDa active form of caspase-3 (a). (D) Percentage of cells that were enucleated on day 17. (E) Percentage of apoptotic cells in the culture at various times (N indicates negative control; P, positive control, S, caspase-3 siRNA-1 treated; M, mock transfected control).