Antagonism between DNA hypermethylation and enhancer-blocking activity at the H19 DMD is uncovered by CpG mutations.
Imprinted expression at the H19-Igf2 locus depends on a differentially methylated domain (DMD) that acts both as a maternal-specific, methylation-sensitive insulator and as a paternal-specific site of hypermethylation. Four repeats in the DMD bind CCCTC-binding factor (CTCF) on the maternal allele and have been proposed to attract methylation on the paternal allele. We introduced point mutations into the DMD to deplete the repeats of CpGs while retaining CTCF-binding and enhancer-blocking activity. Maternal inheritance of the mutations left H19 expression and Igf2 imprinting intact, consistent with the idea that the DMD acts as an insulator. Conversely, paternal inheritance of these mutations disrupted maintenance of DMD methylation, resulting in biallelic H19 expression. Furthermore, an insulator was established on the paternally inherited mutated allele in vivo, reducing Igf2 expression and resulting in a 40% reduction in size of newborn offspring. Thus, the nine CpG mutations in the DMD showed that the two parental-specific roles of the H19 DMD, methylation maintenance and insulator assembly, are antagonistic.
Howard Hughes Medical Institute and Department of Cell and Developmental Biology, University of Pennsylvania School of Medicine, Philadelphia, Pennsylvania 19104, USA.
Nora
N
Engel
Adam G
AG
West
Gary
G
Felsenfeld
Marisa S
MS
Bartolomei
D000818:Animals; D000831:Animals, Newborn; D001483:Base Sequence; D001724:Birth Weight / Q000235:genetics; D000076246:CCCTC-Binding Factor; D018899:CpG Islands / Q000235:genetics*; D019175:DNA Methylation; D004268:DNA-Binding Proteins / Q000235:genetics; D004742:Enhancer Elements, Genetic; D005260:Female; D015870:Gene Expression; D018392:Genomic Imprinting; D007335:Insulin-Like Growth Factor II / Q000235:genetics*; D008297:Male; D051379:Mice; D017354:Point Mutation; D012097:Repressor Proteins / Q000235:genetics
D000076246:CCCTC-Binding Factor; C000619698:Ctcf protein, mouse; D004268:DNA-Binding Proteins; D012097:Repressor Proteins; D007335:Insulin-Like Growth Factor II