title: Role of histone methyltransferase G9a in CpG methylation of the Prader-Willi syndrome imprinting center.
abstract: Imprinted genes in mammals are often located in clusters whose imprinting is subject to long range regulation by cis-acting sequences known as imprinting centers (ICs). The mechanisms by which these ICs exert their effects is unknown. The Prader-Willi syndrome IC (PWS-IC) on human chromosome 15 and mouse chromosome 7 regulates imprinted gene expression bidirectionally within an approximately 2-megabase region and shows CpG methylation and histone H3 Lys-9 methylation in somatic cells specific for the maternal chromosome. Here we show that histone H3 Lys-9 methylation of the PWS-IC is reduced in mouse embryonic stem (ES) cells lacking the G9a histone H3 Lys-9/Lys-27 methyltransferase and that maintenance of CpG methylation of the PWS-IC in mouse ES cells requires the function of G9a. We show by RNA fluorescence in situ hybridization (FISH) that expression of Snrpn, an imprinted gene regulated by the PWS-IC, is biallelic in G9a -/- ES cells, indicating loss of imprinting. By contrast, Dnmt1 -/- ES cells lack CpG methylation of the PWS-IC but have normal levels of H3 Lys-9 methylation of the PWS-IC and show normal monoallelic Snrpn expression. Our results demonstrate a role for histone methylation in the maintenance of parent-specific CpG methylation of imprinting regulatory regions and suggest a possible role of histone methylation in establishment of these CpG methylation patterns.
authors.affiliation: Departments of Biochemistry and Molecular Genetics and Pediatrics, University of Virginia, Charlottesville, Virginia 22908-0733, USA.
authors.forename: Zhenghan
authors.initials: Z
authors.lastname: Xin
authors.forename: Makoto
authors.initials: M
authors.lastname: Tachibana
authors.forename: Michele
authors.initials: M
authors.lastname: Guggiari
authors.forename: Edith
authors.initials: E
authors.lastname: Heard
authors.forename: Yoichi
authors.initials: Y
authors.lastname: Shinkai
authors.forename: Joseph
authors.initials: J
authors.lastname: Wagstaff
mesh_terms: D000818:Animals; D001324:Autoantigens; D002460:Cell Line; D019175:DNA Methylation; D015226:Dinucleoside Phosphates / Q000378:metabolism*; D004622:Embryo, Mammalian; D018392:Genomic Imprinting; D000076983:Histone Methyltransferases; D011495:Histone-Lysine N-Methyltransferase; D006657:Histones / Q000378:metabolism; D017404:In Situ Hybridization, Fluorescence; D008780:Methyltransferases / Q000502:physiology*; D051379:Mice; D011218:Prader-Willi Syndrome / Q000235:genetics*; D011496:Protein Methyltransferases; D012097:Repressor Proteins / Q000502:physiology; D017411:Ribonucleoproteins, Small Nuclear / Q000378:metabolism; D013234:Stem Cells / Q000378:metabolism; D019076:Transgenes; D055517:snRNP Core Proteins
chemical_list: D001324:Autoantigens; D015226:Dinucleoside Phosphates; D000076983:Histone Methyltransferases; D011495:Histone-Lysine N-Methyltransferase; D006657:Histones; D008780:Methyltransferases; D011496:Protein Methyltransferases; D012097:Repressor Proteins; D017411:Ribonucleoproteins, Small Nuclear; D055517:snRNP Core Proteins; C526417:SNRPN protein, human; C015772:CpG dinucleotide