Overexpression of the decoy CTCF abolishes the IGF2/H19 ICR binding of the endogenous CTCF. The expression of decoy CTCF was measured by RT-PCR (A and B), fluorescence microscopy (C), and Western blotting (D). Binding of endogenous CTCF and decoy CTCFs to the ICR was detected by ChIP using two antibodies that recognize the CT and ZF regions of CTCF, respectively (E and F, CTCF sites 1 and 3; and G, CTCF site 6). The competitive binding of native CTCF and ZF-EGFP to the sixth site was detected by a GFP antibody that specifically recognizes the ZF-EGFP and an antibody against the CTCF CT domain (H). Bars, 400 µm.