Project description:To identify the roles of silencers in generating and maintaining epigenetic states, we utilized FACS to sort cells that exhibited different epigenetic states, and ChIP to survey the chromatin architecture of a locus in these cells. Additional experiments involve modulation of silencing factors and phenotypic measurements such as transcription of the locus of interest and ChIP of silencing factors at that locus.
Project description:Heritable heterochromatin domain formation is initiated by dynamic changes in the proteome on specialized loci, leading to chromatin modifier recruitment, heterochromatin assembly and propagation. Here we characterize the proteomes associated with a defined heterochromatin nucleation region in three distinct chromatin states: before de novo H3K9 methylation nucleation, following heterochromatin assembly and upon heterochromatin disassembly. Our analyses separate sequence-dependent from sequence-independent processes, providing a systematic examination of the template-driven nucleation and epigenetic wiring underlying heterochromatin transmission. We identify functional interactions that reveal an integral role for the conserved nucleolytic Grc3 complex, and its associated network, as pioneer factors in heterochromatin assembly. More broadly, we demonstrate the power of quantitative proteomics-based strategies for the unbiased scrutiny of the single regions assembled in distinct chromatin states.
Project description:Epigenetic inheritance of heterochromatin requires DNA sequence-independent propagation mechanisms, coupling to RNAi, or input from DNA sequence, but how DNA contributes to inheritance is not understood. Here, we identify a DNA element (termed “maintainer”) that is sufficient for epigenetic inheritance of preexisting histone H3 lysine 9 methylation (H3K9me) and heterochromatin in Schizosaccharomyces pombe, but cannot establish de novo gene silencing in wild-type cells. This maintainer is a composite DNA element with binding sites for the Atf1/Pcr1 and Deb1 transcription factors and the Origin Recognition Complex (ORC), located within a 130-base pair region, and can be converted to a silencer in cells with lower rates of H3K9me turnover, suggesting that it participates in recruiting the H3K9 methyltransferase Clr4/Suv39h. These results suggest that, in the absence of RNAi, histone H3K9me is only heritable when it can collaborate with maintainer-associated DNA-binding proteins that help recruit the enzyme responsible for its epigenetic deposition.
Project description:Epigenetic inheritance of heterochromatin requires sequence - independent propagation mechanisms and input from DNA sequence, but how DNA contributes to inheritance is not understood. Here, we identify a DNA element ( term ed the “maintainer” ) that is necessary and sufficient for epigenetic inheritance of preexisting histone H3 lysine 9 methylation (H3K9me) and heterochromatin i n the fission yeast Schizosaccharomyces pombe . In wild - type cells, d espite its requirement for maintenance of H3K9me, the maintainer cannot establish de novo gene silencing. The maintainer is a composite 1307 - base pair DNA element with binding sites for the Atf1/Pcr1 and Deb1 transcription factors and the O rigin R ecognition C omplex (ORC) and can be converted to a silencer in cells with lower rates of H3K9me turnover , suggesting that it participate s in recruiting the H3K9 methyltransferase Clr4 / Suv39h . T hese results suggest tha t histone H3K9me is only heritable when it can collaborate with maintainer - associated DNA - binding proteins that help recruit the enzyme responsible for its epigenetic deposition .
Project description:Pluripotent states of embryonic stem cells (ESCs) with distinct transcription profile affect their differentiation capacity and therapeutic potential. By single cell analysis of high-resolution three-dimensional (3D) genome structure, we show that remodeling genome structure is highly associated with pluripotent states of human ESCs (hESCs). Naive pluripotent state is featured with specialized 3D genome structures and clear chromatin compartmentation distinct from primed state. Naive pluripotent state may be achieved by remodeled active euchromatin compartment and less chromatin interaction in the nuclear center. This unique genome organization is linked to elevated chromatin accessibility on enhancers and thus high expression levels of naive pluripotent genes localized in this region. On the contrary, primed state exhibits intermingled genome organization. Moreover, active euchromatin and primed pluripotent genes are distributed in the nuclear periphery and yet repressive heterochromatin densely concentrated in the nuclear center, reducing chromatin accessibility and transcription of naive genes. Thus, inversion or relocation of heterochromatin to euchromatin compartmentation is related to regulating chromatin accessibility and thus define pluripotent states and cell identity.
Project description:Pluripotent states of embryonic stem cells (ESCs) with distinct transcription profile affect their differentiation capacity and therapeutic potential. By single cell analysis of high-resolution three-dimensional (3D) genome structure, we show that remodeling genome structure is highly associated with pluripotent states of human ESCs (hESCs). Naive pluripotent state is featured with specialized 3D genome structures and clear chromatin compartmentation distinct from primed state. Naive pluripotent state may be achieved by remodeled active euchromatin compartment and less chromatin interaction in the nuclear center. This unique genome organization is linked to elevated chromatin accessibility on enhancers and thus high expression levels of naive pluripotent genes localized in this region. On the contrary, primed state exhibits intermingled genome organization. Moreover, active euchromatin and primed pluripotent genes are distributed in the nuclear periphery and yet repressive heterochromatin densely concentrated in the nuclear center, reducing chromatin accessibility and transcription of naive genes. Thus, inversion or relocation of heterochromatin to euchromatin compartmentation is related to regulating chromatin accessibility and thus define pluripotent states and cell identity.
Project description:Histone H3 lysine 9 (H3K9) methylation is a central epigenetic modification that defines heterochromatin from unicellular to multicellular organisms. In mammalian cells, H3K9 methylation can be catalyzed by at least six distinct SET domain enzymes: Suv39h1/Suv39h2, Eset1/Eset2 and G9a/Glp. We used mouse embryonic fibroblasts (MEFs) with a conditional mutation for Eset1 and introduced progressive deletions for the other SET domain genes by CRISPR/Cas9 technology. Compound mutant MEFs for all 6 SET domain methyltransferase (KMT) genes lack all H3K9 methylation states, derepress nearly all families of repeat elements and display genomic instabilities. Strikingly, the 6KO H3K9 KMT MEFs no longer maintain heterochromatin organization and have lost electron-dense heterochromatin. This is the first analysis of H3K9 methylation deficient mammalian chromatin and reveals a crucial function for H3K9 methylation in protecting heterochromatin organization and genome integrity.
Project description:Heterochromatin, a highly compact chromatin state characterized by histone H3 lysine 9 methylation (H3K9me) and HP1 protein binding, epigenetically silences the underlying DNA and influences the expression of neighboring genes. Therefore the sites of heterochromatin assembly and its subsequent spreading are generally precisely determined. Here we show that in fission yeast, the combined absence of anti-silencing factors Mst2 and Epe1 results in uncontrolled heterochromatin spreading and severe growth defects. Interestingly, these cells quickly recover by accumulating H3K9me at the clr4+ locus, which encodes the H3K9 methyltransferase essential for heterochromatin assembly, thereby leading to reduced expression of Clr4 to restrain heterochromatin spreading. Preventing H3K9me at the clr4+ locus resulted in the accumulation of H3K9me at the rik1+ locus, which encodes another component of the Clr4 complex essential for H3K9me. Our results demonstrate that promiscuous heterochromatin assembly enables fast adaptation in response to changes in chromatin landscape and illustrate a negative feedback mechanism by which cells counteract toxic heterochromatin accumulation.
Project description:Pluripotent states of embryonic stem cells (ESCs) with distinct transcription profile affect their differentiation capacity and therapeutic potential. By single cell analysis of high-resolution three-dimensional (3D) genome structure, we show that remodeling genome structure is highly associated with pluripotent states of human ESCs (hESCs). Naive pluripotent state is featured with specialized 3D genome structures and clear chromatin compartmentation distinct from primed state. Naive pluripotent state may be achieved by remodeled active euchromatin compartment and less chromatin interaction in the nuclear center. This unique genome organization is linked to elevated chromatin accessibility on enhancers and thus high expression levels of naive pluripotent genes localized in this region. On the contrary, primed state exhibits intermingled genome organization. Moreover, active euchromatin and primed pluripotent genes are distributed in the nuclear periphery and yet repressive heterochromatin densely concentrated in the nuclear center, reducing chromatin accessibility and transcription of naive genes. Thus, inversion or relocation of heterochromatin to euchromatin compartmentation is related to regulating chromatin accessibility and thus define pluripotent states and cell identity.