Multiple imprinted sense and antisense transcripts, differential methylation and tandem repeats in a putative imprinting control region upstream of mouse  Igf2

Abstract

The mouse insulin-like growth factor 2 (Igf2) locus is a complex genomic region that produces multiple transcripts from alternative promoters. Expression at this locus is regulated by parental imprinting. However, despite the existence of putative imprinting control elements in the Igf2 upstream region, imprinted transcriptional repression is abolished by null mutations at the linked H19 locus. To clarify the extent to which the Igf2 upstream region contains autonomous imprinting control elements we have performed functional and comparative analyses of the region in the mouse and human. Here we report the existence of multiple, overlapping imprinted (maternally repressed) sense and antisense transcripts that are associated with a tandem repeat in the mouse Igf2 upstream region. Regions f lanking the repeat exhibit tissue-specific parental allelic methylation patterns, suggesting the existence of tissue-specific control elements in the upstream region. Studies in H19 null mice indicate that both parental allelic methylation and monoallelic expression of the upstream transcripts depends on an intact H19 gene acting in cis. The homologous region in human IGF2 is structurally conserved, with the significant exception that it does not contain a tandem repeat. Our results support the proposal that tandem repeats act to target methylation to imprinted genetic loci.

Relaxation of IGF2 imprinting in Wilms tumours associated with specific changes in IGF2 methylation

“…In contrast we have shown that the homologous region of the human IGF2 gene (between exons 3 and 4) was unmethylated on both alleles in normal kidney and Wilms tumours. As already noted above, another region of di erential methylation (dmr 0) in the mouse Igf2 gene was recently identi®ed on the maternal allele near the mouse pseudo-exon 2 (Moore et al, 1997). We have shown that the homologous region in the human is also methylated on the maternal allele and that loss of imprinting is associated with loss of methylation from this region.…”

“…We have shown that relaxation of IGF2 imprinting in Wilms tumours is accompanied by loss of methylation from the maternal allele in a region spanning 2 kb of DNA located upstream of the imprinted promoter complex. This region is homologous to a region of maternal allelespeci®c methylation (dmr 0), previously identi®ed in the mouse IGF2 gene (Moore et al, 1997). Analysis of the remainder of the IGF2 gene identi®ed no other regions of di erential methylation.…”

“…Previous methylation studies of the mouse Igf2 gene have identi®ed three di erentially methylated regions (dmrs) (Moore et al, 1997). Two of these regions, dmr 0 and dmr 1, are located upstream of exon 1 of mouse Igf2; dmr 0 is methylated on the inactive maternal allele, while dmr 1 is methylated on the active paternal allel (Figure 1).…”

Plant SET domain-containing proteins: Structure, function and regulation

“…In eukaryotic cells, such RNAs are known to be mostly involved in genomic imprinting [150] and X chromosome inactivation [151]. The discovery that AS transcription is more widespread than previously thought challenges this view and suggests that dsRNA may play a more general role (or perhaps a wider role) in regulation of gene expression.…”

IGF2: Epigenetic regulation and role in development and disease

“…There is mounting evidence that non-coding (especially antisense) RNAs regulate allele-specific gene expression (reviewed in [30]). Multiple sense and antisense transcripts have been detected in the mouse Igf2 5' region, and the major antisense transcript, Igf2AS, is paternally expressed and noncoding [41]. An antisense message transcribed from a homologous region near human IGF2 encodes a putative 273-amino acid protein of unknown function [42].…”