Transcription is required for establishment of germline methylation marks at imprinted genes.
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.
Chotalia
Mita
M
Laboratory of Developmental Genetics and Imprinting, The Babraham Institute, Cambridge CB22 3AT, United Kingdom.
Smallwood
Sebastien A
SA
Ruf
Nico
N
Dawson
Claire
C
Lucifero
Diana
D
Frontera
Marga
M
James
Katherine
K
Dean
Wendy
W
Kelsey
Gavin
G
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*
D002864:Chromogranins; C498642:Gnas protein, mouse; D019205:GTP-Binding Protein alpha Subunits, Gs