GENOMIC STRUCTURE AND PARENT-OF-ORIGIN-SPECIFIC METHYLATION OF PEG1

We previously identified Peg1/Mest as a novel paternally expressed gen e in the developing mouse embryo, The human PEG1 gene was recently ass igned to 7q32 and shown to be imprinted and paternally expressed. Ther efore, PEG1 deficiency could participate in the aetiology of pre-and p ost-natal growth retardation associated with maternal uniparental diso my 7 in humans, We have now initiated the characterization of the Peg1 locus in order to identify and dissect cis-acting elements implicated in its imprinted monoallelic expression. The genomic structure of Peg 1 as well as the DNA sequence of the 5'-end of the gene, including 2.4 kb of promoter sequences and covering the first 2 exons, have been de termined. important sequence elements, such as a CpG island spanning e xon 1 and direct repeats, are identified and discussed. To address the role of epigenetic modifications in the imprinting of Peg1, a methyla tion analysis of the Peg1 gene is presented. partially methylated cyto sine residues in 13.5 d.p.c. embryos and undifferentiated ES cells wer e identified, Using embryos carrying a targetted mutation at the Peg1 locus, we show that this partial promoter methylation pattern reflects a strict parent-of-origin-specific differential methylation: the expr essed paternal allele is unmethylated, whereas the silenced maternal a llele is fully methylated at the CpG sites studied, That the gametes c arry the epigenetic information necessary to lay down this allele-spec ific methylation pattern is suggested by analysis of DNA isolated from sperm and parthenogenetic embryos.