Site-directed mutagenesis destroyed the eight CpG islands outside of the CTCF sites. A floxed neomycin resistance gen cassette inserted downstream of the modified sequence was removed by cre-mediated recombination removed. The CpG content of the imprinting control region (ICR) is reduced 16% without changing the size of the ICR or disrupting the CTCF sites. (J:173610)