title: Tissue-specific insulator function at H19/Igf2 revealed by deletions at the imprinting control region.
abstract: Parent-of-origin-specific expression at imprinted genes is regulated by allele-specific DNA methylation at imprinting control regions (ICRs). This mechanism of gene regulation, where one element controls allelic expression of multiple genes, is not fully understood. Furthermore, the mechanism of gene dysregulation through ICR epimutations, such as loss or gain of DNA methylation, remains a mystery. We have used genetic mouse models to dissect ICR-mediated genetic and epigenetic regulation of imprinted gene expression. The H19/insulin-like growth factor 2 (Igf2) ICR has a multifunctional role including insulation, activation and repression. Microdeletions at the human H19/IGF2 ICR (IC1) are proposed to be responsible for IC1 epimutations associated with imprinting disorders such as Beckwith-Wiedemann syndrome (BWS). Here, we have generated and characterized a mouse model that mimics BWS microdeletions to define the role of the deleted sequence in establishing and maintaining epigenetic marks and imprinted expression at the H19/IGF2 locus. These mice carry a 1.3 kb deletion at the H19/Igf2 ICR [Δ2,3] removing two of four CCCTC-binding factor (CTCF) sites and the intervening sequence, ∼75% of the ICR. Surprisingly, the Δ2,3 deletion does not perturb DNA methylation at the ICR; however, it does disrupt imprinted expression. While repressive functions of the ICR are compromised by the deletion regardless of tissue type, insulator function is only disrupted in tissues of mesodermal origin where a significant amount of CTCF is poly(ADP-ribosyl)ated. These findings suggest that insulator activity of the H19/Igf2 ICR varies by cell type and may depend on cell-specific enhancers as well as posttranslational modifications of the insulator protein CTCF.
authors.affiliation: Department of Cell and Developmental Biology, University of Pennsylvania Perelman School of Medicine, 9-123 SCTR, 3400 Civic Center Boulevard, Philadelphia PA 19104, USA and Department of Genetics, University of North Carolina at Chapel Hill, 120 Mason Farm Road, Chapel Hill, NC 27599, USA.
authors.forename: Folami Y
authors.initials: FY
authors.lastname: Ideraabdullah
authors.affiliation: Department of Cell and Developmental Biology, University of Pennsylvania Perelman School of Medicine, 9-123 SCTR, 3400 Civic Center Boulevard, Philadelphia PA 19104, USA and.
authors.forename: Joanne L
authors.initials: JL
authors.lastname: Thorvaldsen
authors.affiliation: Department of Cell and Developmental Biology, University of Pennsylvania Perelman School of Medicine, 9-123 SCTR, 3400 Civic Center Boulevard, Philadelphia PA 19104, USA and.
authors.forename: Jennifer A
authors.initials: JA
authors.lastname: Myers
authors.affiliation: Department of Cell and Developmental Biology, University of Pennsylvania Perelman School of Medicine, 9-123 SCTR, 3400 Civic Center Boulevard, Philadelphia PA 19104, USA and bartolom@mail.med.upenn.edu.
authors.forename: Marisa S
authors.initials: MS
authors.lastname: Bartolomei
mesh_terms: D000818:Animals; D001483:Base Sequence; D001506:Beckwith-Wiedemann Syndrome / Q000235:genetics*; D000076246:CCCTC-Binding Factor; D019175:DNA Methylation; D044127:Epigenesis, Genetic; D018392:Genomic Imprinting; D006801:Humans; D038101:Insulator Elements; D007335:Insulin-Like Growth Factor II / Q000235:genetics* / Q000378:metabolism; D051379:Mice; D008822:Mice, Transgenic; D009154:Mutation; D009928:Organ Specificity; D012097:Repressor Proteins / Q000378:metabolism; D017384:Sequence Deletion
chemical_list: D000076246:CCCTC-Binding Factor; C000619697:CTCF protein, human; C000619698:Ctcf protein, mouse; C513121:IGF2 protein, mouse; D012097:Repressor Proteins; D007335:Insulin-Like Growth Factor II