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

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

^*Department of Development and Genetics, The Babraham Institute, Cambridge CB2 4AT, United Kingdom; and ^‡Institute of Genetic Information, Kyushu University, Maidashi 3–1-1, Higashi-ku, Fukuoka 812, Japan

Edited by Shirley M. Tilghman, Princeton University, Princeton, NJ, and approved September 16, 1997 (received for review June 24, 1997)

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 flanking 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.

Footnotes

↵ † To whom reprint requests should be addressed. e-mail: tmoore{at}bbsrc.ac.uk.
↵ § Present address: Institut National de la Santé et de la Recherche Médicale, Unité 124, Institut de recherches sur le cancer de Lille, Place de Verdun, 59045 Lille, France.
This paper was submitted directly (Track II) to the Proceedings Office.
Abbreviations: HS, hypersensitive sites; DMR, differentially methylated regions; RACE, rapid amplification of cDNA ends; UP, upper primer; LP, lower primer; RT, reverse transcription; AS, antisense; DSS, donor splice site; ASS, acceptor splice site; P1, promoter 1; RP, RACE primer; B6CBF₁, (C57BL/6 × CBA)F₁; BE, BamHI–EcoRI; H1–5, HpaII sites 1–5.
Data deposition: The sequence reported in this paper has been deposited in the GenBank database (accession no. Y13633).