title: The SRA protein Np95 mediates epigenetic inheritance by recruiting Dnmt1 to methylated DNA.
abstract: DNA methyltransferase (cytosine-5) 1 (Dnmt1) is the principal enzyme responsible for maintenance of CpG methylation and is essential for the regulation of gene expression, silencing of parasitic DNA elements, genomic imprinting and embryogenesis. Dnmt1 is needed in S phase to methylate newly replicated CpGs occurring opposite methylated ones on the mother strand of the DNA, which is essential for the epigenetic inheritance of methylation patterns in the genome. Despite an intrinsic affinity of Dnmt1 for such hemi-methylated DNA, the molecular mechanisms that ensure the correct loading of Dnmt1 onto newly replicated DNA in vivo are not understood. The Np95 (also known as Uhrf1 and ICBP90) protein binds methylated CpG through its SET and RING finger-associated (SRA) domain. Here we show that localization of mouse Np95 to replicating heterochromatin is dependent on the presence of hemi-methylated DNA. Np95 forms complexes with Dnmt1 and mediates the loading of Dnmt1 to replicating heterochromatic regions. By using Np95-deficient embryonic stem cells and embryos, we show that Np95 is essential in vivo to maintain global and local DNA methylation and to repress transcription of retrotransposons and imprinted genes. The link between hemi-methylated DNA, Np95 and Dnmt1 thus establishes key steps of the mechanism for epigenetic inheritance of DNA methylation.
authors.affiliation: Tohoku University Biomedical Engineering Research Organization (TUBERO), 2-1 Seiryo-machi, Aoba-ku, Sendai 980-8575, Japan.
authors.forename: Jafar
authors.initials: J
authors.lastname: Sharif
authors.forename: Masahiro
authors.initials: M
authors.lastname: Muto
authors.forename: Shin-ichiro
authors.initials: S
authors.lastname: Takebayashi
authors.forename: Isao
authors.initials: I
authors.lastname: Suetake
authors.forename: Akihiro
authors.initials: A
authors.lastname: Iwamatsu
authors.forename: Takaho A
authors.initials: TA
authors.lastname: Endo
authors.forename: Jun
authors.initials: J
authors.lastname: Shinga
authors.forename: Yoko
authors.initials: Y
authors.lastname: Mizutani-Koseki
authors.forename: Tetsuro
authors.initials: T
authors.lastname: Toyoda
authors.forename: Kunihiro
authors.initials: K
authors.lastname: Okamura
authors.forename: Shoji
authors.initials: S
authors.lastname: Tajima
authors.forename: Kohzoh
authors.initials: K
authors.lastname: Mitsuya
authors.forename: Masaki
authors.initials: M
authors.lastname: Okano
authors.forename: Haruhiko
authors.initials: H
authors.lastname: Koseki
mesh_terms: D000818:Animals; D022762:CCAAT-Enhancer-Binding Proteins; D018899:CpG Islands / Q000235:genetics; D004247:DNA / Q000737:chemistry / Q000378:metabolism*; D000076123:DNA (Cytosine-5-)-Methyltransferase 1; D004248:DNA (Cytosine-5-)-Methyltransferases / Q000378:metabolism*; D019175:DNA Methylation; D004261:DNA Replication; D053595:Embryonic Stem Cells / Q000378:metabolism; D044127:Epigenesis, Genetic; D018392:Genomic Imprinting; D006367:HeLa Cells; D006570:Heterochromatin / Q000235:genetics / Q000378:metabolism; D006801:Humans; D051379:Mice; D009687:Nuclear Proteins / Q000737:chemistry* / Q000172:deficiency / Q000235:genetics / Q000378:metabolism*; D018809:Proliferating Cell Nuclear Antigen / Q000378:metabolism; D017434:Protein Structure, Tertiary; D018626:Retroelements / Q000235:genetics; D014158:Transcription, Genetic; D044767:Ubiquitin-Protein Ligases
chemical_list: D022762:CCAAT-Enhancer-Binding Proteins; D006570:Heterochromatin; D009687:Nuclear Proteins; D018809:Proliferating Cell Nuclear Antigen; D018626:Retroelements; D004247:DNA; D000076123:DNA (Cytosine-5-)-Methyltransferase 1; D004248:DNA (Cytosine-5-)-Methyltransferases; C000619380:DNMT1 protein, human; C000619381:Dnmt1 protein, mouse; D044767:Ubiquitin-Protein Ligases; C117054:Uhrf1 protein, mouse