Project description:To understand what dictates the emerging patterns of de novo DNA methylation, we mapped DNA methylation, chromatin, and transcription changes in purified fetal mouse germ cells using MIRA-chip, ChIP-chip, and strand-specific RNA-seq, respectively. De novo methylation occurred without any apparent trigger from preexisting repressing chromatin marks but was preceded by broad, low-level transcription along the entire genome in prospermatogonia. Only distinct short sequences remained unmethylated, precisely aligned with constitutive or emerging peaks of H3K4me2. Establishment of methylation at differentially methylated regions (DMRs) of imprinted genes, CpG islands, and IAPs followed these same default rules. Transcription run-through occurred at paternal DMRs with no- or diminishing H3K4me2 peaks. Maternal DMRs remained unmethylated among highly methylated DNA at precisely aligned H3K4me2 peaks with transcription initiating at least in one strand. Our results suggest that the pattern of de novo DNA methylation in prospermatogonia is dictated by opposing actions of broad, low-level transcription and dynamic patterns of active chromatin. ChIP-chip and MIRA-chip were performed to map histone modifications and DNA methylation at different devlopmental time points in germ cells and somatic cells along known imprinted domains and control regions, using custom NimbleGen tiling arrays.
Project description:This SuperSeries is composed of the SubSeries listed below. DNA methylation is an epigenetic modification associated with transcriptional repression of promoters and is essential for mammalian development. Establishment of DNA methylation is mediated by the de novo DNA methyltransferases DNMT3A and DNMT3B, whereas DNMT1 ensures maintenance of methylation through replication. Absence of these enzymes is lethal, and somatic mutations in these genes have been associated with several human diseases. How genomic DNA methylation patterns are regulated remains poorly understood, as the mechanisms that guide recruitment and activity of DNMTs in vivo are largely unknown. To gain insights into this matter we determined chromosomal binding and site-specific activity of the mammalian de novo DNA methyltransferases DNMT3A and DNMT3B. We show that both enzymes localize to methylated, CpG dense regions in mouse stem cells, yet are excluded from active promoters and enhancers. By specifically measuring sites of de novo methylation, we observe that enzymatic activity reflects chromosomal binding. De novo methylation increases with CpG density, yet is excluded from nucleosomes. Notably, we observed selective binding of DNMT3B to the bodies of transcribed genes, which leads to their preferential methylation. This targeting to transcribed sequences requires SETD2-mediated methylation of lysine 36 on histone H3 and a functional PWWP domain of DNMT3B. Together these findings reveal how sequence and chromatin cues guide de novo methyltransferase activity to ensure methylome integrity. Refer to individual Series
Project description:DNA methylation is an epigenetic modification associated with transcriptional repression of promoters and is essential for mammalian development. Establishment of DNA methylation is mediated by the de novo DNA methyltransferases DNMT3A and DNMT3B, whereas DNMT1 ensures maintenance of methylation through replication. Absence of these enzymes is lethal, and somatic mutations in these genes have been associated with several human diseases. How genomic DNA methylation patterns are regulated remains poorly understood, as the mechanisms that guide recruitment and activity of DNMTs in vivo are largely unknown. To gain insights into this matter we determined chromosomal binding and site-specific activity of the mammalian de novo DNA methyltransferases DNMT3A and DNMT3B. We show that both enzymes localize to methylated, CpG dense regions in mouse stem cells, yet are excluded from active promoters and enhancers. By specifically measuring sites of de novo methylation, we observe that enzymatic activity reflects chromosomal binding. De novo methylation increases with CpG density, yet is excluded from nucleosomes. Notably, we observed selective binding of DNMT3B to the bodies of transcribed genes, which leads to their preferential methylation. This targeting to transcribed sequences requires SETD2-mediated methylation of lysine 36 on histone H3 and a functional PWWP domain of DNMT3B. Together these findings reveal how sequence and chromatin cues guide de novo methyltransferase activity to ensure methylome integrity. Whole-genome bisulfite sequencing for Dnmt1,3a,3b-triple-KO ES cells expressing DNMT3A2 or DNMT3B1 and for Dnmt1,3a,3b,Setd2-KO ES cells expressing DNMT3B1
Project description:Erasure and subsequent re-instatement of DNA methylation in the germline, especially at imprinted CpG islands (CGIs), is crucial to embryogenesis in mammals. The mechanisms underlying DNA methylation establishment remain poorly understood, but a number of post-translational modifications of histones are implicated in antagonizing or recruiting the de novo DNA methylation complex. In mouse oogenesis, DNA methylation establishment occurs on a largely unmethylated genome and in non-dividing cells, making it a highly informative model for examining how histone modifications can shape the DNA methylome. Using a chromatin immunoprecipitation and genome-wide sequencing (ChIP-Seq) protocol optimized for low cell numbers and novel techniques for isolating primary and growing oocytes, profiles were generated for histone modifications implicated in promoting or inhibiting DNA methylation. CGIs destined for DNA methylation show reduced protective H3K4me2 and H3K4me3 in both primary and growing oocytes, while permissive H3K36me3 increases specifically at these CGIs in growing oocytes. Methylome profiling of oocytes deficient in H3K4 demethylases KDM1A or KDM1B indicated that removal of H3K4 methylation is necessary for proper methylation establishment at CGIs. This work represents the first systematic study performing ChIP-Seq in oocytes, and shows that histone remodeling in the mammalian oocyte helps direct de novo DNA methylation events.
Project description:DNA methylation is an epigenetic modification associated with transcriptional repression of promoters and is essential for mammalian development. Establishment of DNA methylation is mediated by the de novo DNA methyltransferases DNMT3A and DNMT3B, whereas DNMT1 ensures maintenance of methylation through replication. Absence of these enzymes is lethal, and somatic mutations in these genes have been associated with several human diseases. How genomic DNA methylation patterns are regulated remains poorly understood, as the mechanisms that guide recruitment and activity of DNMTs in vivo are largely unknown. To gain insights into this matter we determined chromosomal binding and site-specific activity of the mammalian de novo DNA methyltransferases DNMT3A and DNMT3B. We show that both enzymes localize to methylated, CpG dense regions in mouse stem cells, yet are excluded from active promoters and enhancers. By specifically measuring sites of de novo methylation, we observe that enzymatic activity reflects chromosomal binding. De novo methylation increases with CpG density, yet is excluded from nucleosomes. Notably, we observed selective binding of DNMT3B to the bodies of transcribed genes, which leads to their preferential methylation. This targeting to transcribed sequences requires SETD2-mediated methylation of lysine 36 on histone H3 and a functional PWWP domain of DNMT3B. Together these findings reveal how sequence and chromatin cues guide de novo methyltransferase activity to ensure methylome integrity. Genome-wide binding analysis for biotin-tagged DNMT3A2 and DNMT3B and variants in wild type ES, wild type neuroprogenitor cells, ES cells triple-KO for Dnmt1,3a,3b and ES cell mutant for Setd2