title: Transcription is required for establishment of germline methylation marks at imprinted genes.
abstract: Genomic imprinting requires the differential marking by DNA methylation of genes in male and female gametes. In the female germline, acquisition of methylation imprint marks depends upon the de novo methyltransferase Dnmt3a and its cofactor Dnmt3L, but the reasons why specific sequences are targets for Dnmt3a and Dnmt3L are still poorly understood. Here, we investigate the role of transcription in establishing maternal germline methylation marks. We show that at the Gnas locus, truncating transcripts from the furthest upstream Nesp promoter disrupts oocyte-derived methylation of the differentially methylated regions (DMRs). Transcription through DMRs in oocytes is not restricted to this locus but occurs across the prospective DMRs at many other maternally marked imprinted domains, suggesting a common requirement for transcription events. The transcripts implicated here in gametic methylation are protein-coding, in contrast to the noncoding antisense transcripts involved in the monoallelic silencing of imprinted genes in somatic tissues, although they often initiate from alternative promoters in oocytes. We propose that transcription is a third essential component of the de novo methylation system, which includes optimal CpG spacing and histone modifications, and may be required to create or maintain open chromatin domains to allow the methylation complex access to its preferred targets.
authors.affiliation: Laboratory of Developmental Genetics and Imprinting, The Babraham Institute, Cambridge CB22 3AT, United Kingdom.
authors.forename: Mita
authors.initials: M
authors.lastname: Chotalia
authors.forename: Sebastien A
authors.initials: SA
authors.lastname: Smallwood
authors.forename: Nico
authors.initials: N
authors.lastname: Ruf
authors.forename: Claire
authors.initials: C
authors.lastname: Dawson
authors.forename: Diana
authors.initials: D
authors.lastname: Lucifero
authors.forename: Marga
authors.initials: M
authors.lastname: Frontera
authors.forename: Katherine
authors.initials: K
authors.lastname: James
authors.forename: Wendy
authors.initials: W
authors.lastname: Dean
authors.forename: Gavin
authors.initials: G
authors.lastname: Kelsey
mesh_terms: D000483:Alleles; D000818:Animals; D002864:Chromogranins; D019175:DNA Methylation / Q000502:physiology*; D005260:Female; D019205:GTP-Binding Protein alpha Subunits, Gs / Q000378:metabolism; D018392:Genomic Imprinting / Q000235:genetics*; D051379:Mice; D008810:Mice, Inbred C57BL; D008969:Molecular Sequence Data; D009865:Oocytes / Q000378:metabolism*; D014158:Transcription, Genetic / Q000235:genetics*
chemical_list: D002864:Chromogranins; C498642:Gnas protein, mouse; D019205:GTP-Binding Protein alpha Subunits, Gs