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:In the mouse, long-term silencing by CpG island DNA methylation is specifically targeted to germline genes in somatic cells, 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. Furthermore, inactivation of E2f6 leads to a failure to deposit CpG island DNA methylation at these genes during implantation. Finally, we show that 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:Max is an obligate dimerization partner for the Myc transcription factors and for several repressors, such as Mnt, Mxd1-4 and Mga, collectively thought to antagonize Myc function in transcription and oncogenesis. Mga, in particular, is part of the variant Polycomb group repressive complex PRC1.6. Here, we show that ablation of the distinct PRC1.6 subunit Pcgf6 – but not Mga – accelerates Myc-induced lymphomagenesis in Eµ-myc transgenic mice. Unexpectedly, however, Pcgf6 loss shows no significant impact on transcriptional profiles, in neither pre-tumoral B-cells, nor lymphomas. Altogether, these data unravel an unforeseen, Mga- and PRC1.6-independent tumor suppressor activity of Pcgf6.
Project description:Max is an obligate dimerization partner for the Myc transcription factors and for several repressors, such as Mnt, Mxd1-4 and Mga, collectively thought to antagonize Myc function in transcription and oncogenesis. Mga, in particular, is part of the variant Polycomb group repressive complex PRC1.6. Here, we show that ablation of the distinct PRC1.6 subunit Pcgf6 – but not Mga – accelerates Myc-induced lymphomagenesis in Eµ-myc transgenic mice. Unexpectedly, however, Pcgf6 loss shows no significant impact on transcriptional profiles, in neither pre-tumoral B-cells, nor lymphomas. Altogether, these data unravel an unforeseen, Mga- and PRC1.6-independent tumor suppressor activity of Pcgf6.
Project description:CpG island elements are associated with most mammalian gene promoters, yet how they contribute to gene regulation remains poorly understood. Recently it has become clear that a subset of CpG islands in embryonic stem cells can act as polycomb response elements and are recognized by the polycomb silencing systems to regulate the expression of genes involved in pluripotency and early developmental transcription programs. How CpG islands function mechanistically as nucleation sites for polycomb repressive complexes remains unknown. Here we discover that the KDM2B protein, by virtue of its ZF-CxxC DNA binding domain, specifically recognizes non-methylated DNA in CpG islands elements genome-wide. Through a physical interaction with the polycomb repressive complex 1 (PRC1), KDM2B targets PRC1 to CpG islands where it contributes to H2AK119ub1 and gene repression at a subset of polycomb targets. Unexpectedly, we also find that CpG islands are occupied by low levels of PRC1 throughout the genome, suggesting that the KDM2B-PRC1 complex may sample CpG island associated genes for susceptibility to polycomb mediated silencing. These observations demonstrate an unexpected and direct link between recognition of CpG islands by KDM2B and targeting of the polycomb repressive system. This provides the basis for a new model describing the functionality of CpG islands as mammalian PREs. ChIP-Seq to compare KDM2A vs. KDM2B genome-wide binding profiles and to understand the contribution of KDM2B to RING1B nucleation. Binding of Kdm2a and Kdm2b to the genome was examined in wildtype mESC, and Kdm2b and Ring1b in mESC where Kdm2b has been stably knocked down by shRNA.
Project description:CpG island elements are associated with most mammalian gene promoters, yet how they contribute to gene regulation remains poorly understood. Recently it has become clear that a subset of CpG islands in embryonic stem cells can act as polycomb response elements and are recognized by the polycomb silencing systems to regulate the expression of genes involved in pluripotency and early developmental transcription programs. How CpG islands function mechanistically as nucleation sites for polycomb repressive complexes remains unknown. Here we discover that the KDM2B protein, by virtue of its ZF-CxxC DNA binding domain, specifically recognizes non-methylated DNA in CpG islands elements genome-wide. Through a physical interaction with the polycomb repressive complex 1 (PRC1), KDM2B targets PRC1 to CpG islands where it contributes to H2AK119ub1 and gene repression at a subset of polycomb targets. Unexpectedly, we also find that CpG islands are occupied by low levels of PRC1 throughout the genome, suggesting that the KDM2B-PRC1 complex may sample CpG island associated genes for susceptibility to polycomb mediated silencing. These observations demonstrate an unexpected and direct link between recognition of CpG islands by KDM2B and targeting of the polycomb repressive system. This provides the basis for a new model describing the functionality of CpG islands as mammalian PREs.
Project description:Silencing of a subset of germline genes is dependent upon DNA methylation (DNAme) post-implantation. However, these genes are generally hypomethylated in the ICM, implicating alternative silencing pathways before implantation. Indeed, in embryonic stem cells (ESCs), an overlapping set of genes, including germline “genome-defence” (GGD) genes, are upregulated following deletion of the H3K9 methyltransferase SETDB1 or subunits of the non-canonical PRC1 complex PRC1.6. Here, we show that in pre-implantation embryos and naïve ESCs (nESCs), hypomethylated promoters of germline genes bound by the PRC1.6 DNA-binding subunits MGA/MAX/E2F6 are enriched for RING1B-dependent H2AK119ub1 and H3K9me3. Accordingly, silencing of these genes in nESCs shows a greater dependence on PRC1.6 than DNAme. In contrast, GGD genes are hypermethylated in epiblast-like cells and their silencing is dependent upon SETDB1, PRC1.6/RING1B and DNAme, with H3K9me3 and DNAme establishment dependent upon MGA binding. Thus, GGD genes are initially repressed by PRC1.6, with DNAme subsequently engaged in post-implantation embryos.