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2014 ; 23
(23
): 6246-59
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Tissue-specific insulator function at H19/Igf2 revealed by deletions at the
imprinting control region
#MMPMID24990148
Ideraabdullah FY
; Thorvaldsen JL
; Myers JA
; Bartolomei MS
Hum Mol Genet
2014[Dec]; 23
(23
): 6246-59
PMID24990148
show ga
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 [?2,3] removing two of four CCCTC-binding
factor (CTCF) sites and the intervening sequence, ?75% of the ICR. Surprisingly,
the ?2,3 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.