title: CTCF binding is not the epigenetic mark that establishes post-fertilization methylation imprinting in the transgenic H19 ICR.
abstract: Imprinted expression of the mouse Igf2/H19 locus is controlled by parent-of-origin-specific methylation of the imprinting control region (ICR). We previously demonstrated that when placed in a heterologous genomic context, the H19 ICR fragment contains an intrinsic activity that allows it to acquire differential methylation in somatic cells but not in germ cells. In the present study, we investigated the requirements for the CTCF-binding sites of the ICR in the acquisition of post-fertilization methylation. To this end, two mutant ICR fragments were introduced into the human beta-globin locus in a yeast artificial chromosome transgenic mouse (TgM) model: 4xMut had mutations in all four ICR CTCF-binding sites that prevented CTCF binding but retained the methylation target CpG motifs, and -9CG harbored mutations in the CpG motifs within the CTCF-binding sites but each site retained constitutive CTCF-binding activity. In TgM germ cells and pre-implantation blastocysts, the absence of CTCF-binding sites (4xMut) did not lead to hypermethylation of the transgenic H19 ICR. However, after implantation, the mutations of CTCF sites (4xMut and -9CG) affected the maintenance of methylation. These results demonstrated that although the CTCF-binding sites are indispensable for maintenance of the unmethylated state of the maternal ICR in post-implantation embryos, they are not required to establish paternal-allele-specific methylation of the transgenic H19 ICR in pre-implantation embryos.
authors.affiliation: Graduate School of Life and Environmental Sciences, University of Tsukuba, Tsukuba, Ibaraki, Japan.
authors.forename: Hitomi
authors.initials: H
authors.lastname: Matsuzaki
authors.forename: Eiichi
authors.initials: E
authors.lastname: Okamura
authors.forename: Akiyoshi
authors.initials: A
authors.lastname: Fukamizu
authors.forename: Keiji
authors.initials: K
authors.lastname: Tanimoto
mesh_terms: D000818:Animals; D001665:Binding Sites; D001755:Blastocyst; D000076246:CCCTC-Binding Factor; D018899:CpG Islands; D019175:DNA Methylation; D004622:Embryo, Mammalian; D005260:Female; D018392:Genomic Imprinting; D006801:Humans; D007335:Insulin-Like Growth Factor II / Q000235:genetics*; D019901:Locus Control Region; D008297:Male; D051379:Mice; D008822:Mice, Transgenic; D009154:Mutation; D012097:Repressor Proteins / Q000378:metabolism*; D019076:Transgenes; D055544:beta-Globins / Q000235:genetics
chemical_list: D000076246:CCCTC-Binding Factor; C000619697:CTCF protein, human; C000619698:Ctcf protein, mouse; D012097:Repressor Proteins; D055544:beta-Globins; D007335:Insulin-Like Growth Factor II