Disruption of mesodermal enhancers forIgf2in the minute mutant

Abstract

The radiation-induced mutation minute (Mnt) in the mouse leads to intrauterine growth retardation with paternal transmission and has been linked to the distal chromosome 7 cluster of imprinted genes. We show that the mutation is an inversion, whose breakpoint distal to H19 disrupts and thus identifies an enhancer for Igf2 expression in skeletal muscle and tongue, and separates the gene from other mesodermal and extra-embryonic enhancers. Paternal transmission of Mnt leads to drastic downregulation of Igf2 transcripts in all mesodermal tissues and the placenta. Maternal transmission leads to methylation of the H19 differentially methylated region (DMR) and silencing of H19, showing that elements 3′ of H19 can modify the maternal imprint. Methylation of the maternal DMR leads to biallelic expression of Igf2 in endodermal tissues and foetal overgrowth, demonstrating that methylation in vivo can open the chromatin boundary upstream of H19. Our work shows that most known enhancers for Igf2 are located 3′ of H19 and establishes an important genetic paradigm for the inheritance of complex regulatory mutations in imprinted gene clusters.

The imprinted Igf2-Igf2r axis is critical for matching placental microvasculature expansion to fetal growth

“…One limitation is the inability to specifically target circulating levels of IGF2 without impacting on the size of the fetus. The source of circulating IGF2 is likely to be multi-organ, with a deletion of mesodermal Igf2 enhancers resulting in reductions in circulating IGF2 by ∼50% and severe FGR ( Davies et al., 2002 ). Another limitation is the lack of Cre-lines to perform specific genetic manipulations in the placental endothelium.…”

Differential 3D genome architecture and imprinted gene expression: cause or consequence?

“…At the murine Kcnk9-Peg13 imprinted domain, similarly, allele-specific and biallelic CTCF-driven structural interactions are observed in ESCs already (Figure 1D), in which this locus is still largely silent and without Part 2 of 2 mesoderm/endoderm), the paternally expressed genes Igf2 (imprinted in mesoderm/endoderm) and Ins2 [imprinted in yolk sac, [109,110]], and the lncRNA gene Nctc1, which shows paternally biaised expression in muscle [92]. Endodermal (EE) and mesodermal enhancers (ME) [green ovals, [92,111]] activate Igf2 on the paternal chromosome through long-distance functional interactions (green arrows). On the maternal chromosome, these interactions are prevented by the CTCF-binding onto the H19-ICR, which acts as a chromatin boundary [23].…”

Human IGF2 Gene Epigenetic and Transcriptional Regulation: At the Core of Developmental Growth and Tumorigenic Behavior

“…In particular, the IGF2 promoter-specific differentially methylated regions (DMRs 0, 1, 2) partially overlap the IGF2 intronic and exonic sequences, along with the DMR known as “inter-genic- or IG-DMR” or Imprinting Center Region 1, ICR1. This region is located between the IGF2 and H19 genes coding regions and the IGF2 enhancer region downstream from H19 , cumulatively establishing a phylogenetically conserved gene cluster acting as an epigenetic switch [ 19 , 20 , 21 ]. IG-DMR is an allele-dependent DMR (ICR1) containing the binding motif for the epigenetic master regulator CTCF, which, along with the PRC2 complex components (discussed in Section 2 and summarized in Table 1 ).…”