Project description:This SuperSeries is composed of the following subset Series: GSE38305: Promoter DNA methylation couples genome-defense mechanisms to epigenetic reprogramming in the mouse germline (part 1) GSE38306: Promoter DNA methylation couples genome-defence mechanisms to epigenetic reprogramming in the mouse germline (part 2) Refer to individual Series
Project description:In mammals, many germline genes are repressed by epigenetic mechanisms to prevent their illegitimate expression in embryonic and somatic cells. To advance our understanding of the complete mechanisms restricting the expression of germline genes in mammals, we analyzed the chromatin signature of germline genes and performed a genome-wide CRISPR-Cas9 knock-out screen for genes involved in germline gene repression using a reporter system in which GFP is under the control of the epigenetically repressed Dazl germline promoter in mouse embryonic stem cells (ESCs). We showed that the repression of germline genes mainly depends on the polycomb complex PRC1.6 and DNA methylation, which function additively in mouse ESCs. Furthermore, we identified and validated several novel genes involved in the repression of germline genes, and characterized three of them: Usp7, Shfm1 (also known as Sem1) and Erh. Inactivation of Usp7, Shfm1 or Erh led to the upregulation of germline genes, as well as retrotransposons for Shfm1, in mouse ESCs. Functionally, Usp7 acts at two levels: firstly it associates with PRC1.6 components and represses germline genes independently of DNA methylation, and secondly it facilitates DNA methylation deposition at germline genes for long term repression. In summary, our study provides a global view of the epigenetic mechanisms and novel factors required for silencing germline genes in embryonic cells.
Project description:In mouse development, long-term silencing by CpG island DNA methylation is specifically targeted to germline genes, however the molecular mechanisms of this specificity remain unclear. Here we demonstrate that the transcription factor E2F6, a member of the polycomb repressive complex 1.6 (PRC1.6), is critical to target and initiate epigenetic silencing at germline genes in early embryogenesis. Genome-wide, E2F6 binds preferentially to CpG islands in embryonic cells. E2F6 cooperates with MGA to silence a subgroup of germline genes in mouse embryonic stem cells and in vivo, a function that critically depends on the E2F6 marked box domain. Inactivation of E2f6 leads to a failure to deposit CpG island DNA methylation at these genes during implantation. Furthermore, E2F6 is required to initiate epigenetic silencing in early embryonic cells but becomes dispensable for the maintenance in differentiated cells. Our findings elucidate the mechanisms of epigenetic targeting of germline genes and provide a paradigm for how transient repression signals by DNA-binding factors in early embryonic cells are translated into long term epigenetic silencing during mammalian development.
Project description:Mouse primordial germ cells (PGCs) erase global DNA methylation (5mC) as part of the comprehensive epigenetic reprogramming that occurs during PGC development. 5mC plays an important role in maintaining stable gene silencing and repression of transposable elements (TE) but it is not clear how the extensive loss of DNA methylation impacts on gene expression and TE repression in developing PGCs. Using a novel epigenetic disruption and recovery screen and genetic analyses, we identified a core set of germline-specific genes that are dependent exclusively on promoter DNA methylation for initiation and maintenance of developmental silencing. These gene promoters appear to possess a specialised chromatin environment that does not acquire any of the repressive H3K27me3, H3K9me2, H3K9me3 or H4K20me3 histone modifications when silenced by DNA methylation. Intriguingly, this methylation-dependent subset is highly enriched in genes with roles in suppressing TE activity in germ cells. We show that the mechanism for developmental regulation of the germline genome-defence genes involves DNMT3B-dependent de novo DNA methylation. These genes are then activated by lineage-specific promoter demethylation during distinct global epigenetic reprogramming events in migratory (~E8.5) and post-migratory (E10.5-E11.5) PGCs. We propose that genes involved in genome defence are developmentally regulated exclusively by promoter DNA methylation as a sensory mechanism that is coupled to the potential for TE activation during global 5mC erasure, thereby acting as a failsafe to ensure TE suppression and maintain genomic integrity in the germline. Total RNA isolated from control p53-/- or sample Dnmt1-/- (p53-/-) mouse embryonic fibroblasts
Project description:Mouse primordial germ cells (PGCs) erase global DNA methylation (5mC) as part of the comprehensive epigenetic reprogramming that occurs during PGC development. 5mC plays an important role in maintaining stable gene silencing and repression of transposable elements (TE) but it is not clear how the extensive loss of DNA methylation impacts on gene expression and TE repression in developing PGCs. Using a novel epigenetic disruption and recovery screen and genetic analyses, we identified a core set of germline-specific genes that are dependent exclusively on promoter DNA methylation for initiation and maintenance of developmental silencing. These gene promoters appear to possess a specialised chromatin environment that does not acquire any of the repressive H3K27me3, H3K9me2, H3K9me3 or H4K20me3 histone modifications when silenced by DNA methylation. Intriguingly, this methylation-dependent subset is highly enriched in genes with roles in suppressing TE activity in germ cells. We show that the mechanism for developmental regulation of the germline genome-defence genes involves DNMT3B-dependent de novo DNA methylation. These genes are then activated by lineage-specific promoter demethylation during distinct global epigenetic reprogramming events in migratory (~E8.5) and post-migratory (E10.5-E11.5) PGCs. We propose that genes involved in genome defence are developmentally regulated exclusively by promoter DNA methylation as a sensory mechanism that is coupled to the potential for TE activation during global 5mC erasure, thereby acting as a failsafe to ensure TE suppression and maintain genomic integrity in the germline. Total RNA isolated from duplicate independent experiments of NIH/3T3 cells, NIH/3T3 cells exposed to 1uM 5aza-dC, and NIH/3T3 after 14 days recovery after drug withdrawal
Project description:Mouse primordial germ cells (PGCs) erase global DNA methylation (5mC) as part of the comprehensive epigenetic reprogramming that occurs during PGC development. 5mC plays an important role in maintaining stable gene silencing and repression of transposable elements (TE) but it is not clear how the extensive loss of DNA methylation impacts on gene expression and TE repression in developing PGCs. Using a novel epigenetic disruption and recovery screen and genetic analyses, we identified a core set of germline-specific genes that are dependent exclusively on promoter DNA methylation for initiation and maintenance of developmental silencing. These gene promoters appear to possess a specialised chromatin environment that does not acquire any of the repressive H3K27me3, H3K9me2, H3K9me3 or H4K20me3 histone modifications when silenced by DNA methylation. Intriguingly, this methylation-dependent subset is highly enriched in genes with roles in suppressing TE activity in germ cells. We show that the mechanism for developmental regulation of the germline genome-defence genes involves DNMT3B-dependent de novo DNA methylation. These genes are then activated by lineage-specific promoter demethylation during distinct global epigenetic reprogramming events in migratory (~E8.5) and post-migratory (E10.5-E11.5) PGCs. We propose that genes involved in genome defence are developmentally regulated exclusively by promoter DNA methylation as a sensory mechanism that is coupled to the potential for TE activation during global 5mC erasure, thereby acting as a failsafe to ensure TE suppression and maintain genomic integrity in the germline.
Project description:Mouse primordial germ cells (PGCs) erase global DNA methylation (5mC) as part of the comprehensive epigenetic reprogramming that occurs during PGC development. 5mC plays an important role in maintaining stable gene silencing and repression of transposable elements (TE) but it is not clear how the extensive loss of DNA methylation impacts on gene expression and TE repression in developing PGCs. Using a novel epigenetic disruption and recovery screen and genetic analyses, we identified a core set of germline-specific genes that are dependent exclusively on promoter DNA methylation for initiation and maintenance of developmental silencing. These gene promoters appear to possess a specialised chromatin environment that does not acquire any of the repressive H3K27me3, H3K9me2, H3K9me3 or H4K20me3 histone modifications when silenced by DNA methylation. Intriguingly, this methylation-dependent subset is highly enriched in genes with roles in suppressing TE activity in germ cells. We show that the mechanism for developmental regulation of the germline genome-defence genes involves DNMT3B-dependent de novo DNA methylation. These genes are then activated by lineage-specific promoter demethylation during distinct global epigenetic reprogramming events in migratory (~E8.5) and post-migratory (E10.5-E11.5) PGCs. We propose that genes involved in genome defence are developmentally regulated exclusively by promoter DNA methylation as a sensory mechanism that is coupled to the potential for TE activation during global 5mC erasure, thereby acting as a failsafe to ensure TE suppression and maintain genomic integrity in the germline.
Project description:Gametes are highly specialised cells that can give rise to the next generation through their ability to generate a totipotent zygote. In mouse, germ cells are first specified in the developing embryo as primordial germ cells (PGCs) starting around embryonic day (E) 6.25. Following subsequent migration into the developing gonad, PGCs undergo a wave of extensive epigenetic reprogramming at E10.5/E11.5, including genome-wide loss of 5-methylcytosine (5mC). The underlying molecular mechanisms of this process have remained enigmatic leading to our inability to recapitulate this step of germline development in vitro. Using an integrative approach, we show that this complex reprogramming process involves the coordinated interplay between promoter sequence characteristics, DNA (de)methylation, Polycomb (PRC1) complex and both DNA demethylation-dependent and -independent functions of Tet1 to enable the activation of a critical set of germline reprogramming responsive (GRR) genes involved in gamete generation and meiosis. Our results also unexpectedly reveal a role for Tet1 in safeguarding but not driving DNA demethylation in gonadal PGCs. Collectively, our work uncovers a fundamental biological role for gonadal germline reprogramming and identifies the epigenetic principles of the PGC-to-gonocyte transition that will be instructive towards recapitulating complete gametogenesis in vitro.