title: A replication-dependent passive mechanism modulates DNA demethylation in mouse primordial germ cells.
abstract: Germline cells reprogramme extensive epigenetic modifications to ensure the cellular totipotency of subsequent generations and to prevent the accumulation of epimutations. Notably, primordial germ cells (PGCs) erase genome-wide DNA methylation and H3K9 dimethylation marks in a stepwise manner during migration and gonadal periods. In this study, we profiled DNA and histone methylation on transposable elements during PGC development, and examined the role of DNA replication in DNA demethylation in gonadal PGCs. CpGs in short interspersed nuclear elements (SINEs) B1 and B2 were substantially demethylated in migrating PGCs, whereas CpGs in long interspersed nuclear elements (LINEs), such as LINE-1, were resistant to early demethylation. By contrast, CpGs in both LINE-1 and SINEs were rapidly demethylated in gonadal PGCs. Four major modifiers of DNA and histone methylation, Dnmt3a, Dnmt3b, Glp and Uhrf1, were actively repressed at distinct stages of PGC development. DNMT1 was localised at replication foci in nascent PGCs, whereas the efficiency of recruitment of DNMT1 into replication foci was severely impaired in gonadal PGCs. Hairpin bisulphite sequencing analysis showed that strand-specific hemi-methylated CpGs on LINE-1 were predominant in gonadal PGCs. Furthermore, DNA demethylation in SINEs and LINE-1 was impaired in Cbx3-deficient PGCs, indicating abnormalities in G1 to S phase progression. We propose that PGCs employ active and passive mechanisms for efficient and widespread erasure of genomic DNA methylation.
authors.affiliation: Department of Bioscience, School of Science and Technology, Kwansei Gakuin University, 2-1 Gakuen, Sanda, Hyogo 669-1337, Japan.
authors.forename: Rika
authors.initials: R
authors.lastname: Ohno
authors.forename: Megumi
authors.initials: M
authors.lastname: Nakayama
authors.forename: Chie
authors.initials: C
authors.lastname: Naruse
authors.forename: Naoki
authors.initials: N
authors.lastname: Okashita
authors.forename: Osamu
authors.initials: O
authors.lastname: Takano
authors.forename: Makoto
authors.initials: M
authors.lastname: Tachibana
authors.forename: Masahide
authors.initials: M
authors.lastname: Asano
authors.forename: Mitinori
authors.initials: M
authors.lastname: Saitou
authors.forename: Yoshiyuki
authors.initials: Y
authors.lastname: Seki
mesh_terms: D000818:Animals; D001483:Base Sequence; D022762:CCAAT-Enhancer-Binding Proteins; D002868:Chromosomal Proteins, Non-Histone / Q000378:metabolism; D018899:CpG Islands; D000076123:DNA (Cytosine-5-)-Methyltransferase 1; D004248:DNA (Cytosine-5-)-Methyltransferases / Q000378:metabolism; D019175:DNA Methylation; D004261:DNA Replication; D044127:Epigenesis, Genetic; D005854:Germ Cells / Q000378:metabolism*; D011495:Histone-Lysine N-Methyltransferase / Q000378:metabolism; D006657:Histones / Q000378:metabolism; D020084:Long Interspersed Nucleotide Elements; D051379:Mice; D008969:Molecular Sequence Data; D009687:Nuclear Proteins / Q000378:metabolism; D020086:Short Interspersed Nucleotide Elements; D044767:Ubiquitin-Protein Ligases
chemical_list: D022762:CCAAT-Enhancer-Binding Proteins; C453799:Cbx3 protein, mouse; D002868:Chromosomal Proteins, Non-Histone; D006657:Histones; D009687:Nuclear Proteins; D000076123:DNA (Cytosine-5-)-Methyltransferase 1; D004248:DNA (Cytosine-5-)-Methyltransferases; C000619381:Dnmt1 protein, mouse; C513479:GLP protein, mouse; D011495:Histone-Lysine N-Methyltransferase; D044767:Ubiquitin-Protein Ligases; C117054:Uhrf1 protein, mouse
keywords: DNA demethylation; DNA replication; Epigenetic reprogramming; PGCs; Primordial germ cells