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Dynamic and flexible bridging of H3K9me3-nucleosomes via HP1β-dimerization establishes a plastic state of condensed chromatin

ABSTRACT: Histone H3 trimethylation of lysine 9 (H3K9me3) and heterochromatin proteins 1 (HP1) are hallmarks of heterochromatin, a state of compacted DNA essential for genome stability and long-term transcriptional silencing. The mechanisms by which H3K9me3 and HP1 contribute to chromatin compaction have been speculative and controversial. We demonstrate that mammalian HP1β is a prototypic HP1 protein exemplifying most basal chromatin binding and effects. These are caused by dimeric and dynamic interaction with highly enriched H3K9me3 and are modulated by various electrostatic interfaces. Via internucleosomal bridging HP1β specifically interacts with condensed chromatin, which we postulate stabilizes the compacted state. In agreement, HP1β genome-wide localization follows enrichment of H3K9me3 and bridging of chromatin fibers in a cellular context is sufficient for maintaining heterochromatic conformation. Overall, our findings define a fundamental mechanism for chromatin higher order structural changes caused by HP1 proteins, which may contribute to the plastic nature of condensed chromatin.

ORGANISM(S): Mus musculus

PROVIDER: GSE71114 | GEO | 2017/02/10

SECONDARY ACCESSION(S): PRJNA290375

REPOSITORIES: GEO

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HP1β dependent phase separation regulates embryonic stem cells exit from naïve pluripotent state

Project description:Liquid-liquid phase separation has drawn great attention as a physical process that mediates the formation of membraneless organelles in cells to coordinate biological reactions in space and time. Previously, it was proposed that the formation of phase-separated droplets is a unique property of HP1α. Here, we show that HP1β, but not HP1α and HP1ɤ, forms nucleosome dependent phase separated droplets. We demonstrate that H3K9me3 is required for HP1β dependent phase separation. Importantly, HP1β dependent phase separation regulates heterochromatin formation, thus controlling embryonic stem cells differentiation. In response to pluripotency exit, HP1β is phosphorylated at serine 89 recruiting KAP1, a pluripotency regulator, and sequestering it in the heterochromatin compartment. This induces changes in the level of pluripotency factors and triggers pluripotency exit. We propose that such a trapping mechanism creates a fast and dynamic mode of remote control of gene expression to regulate cell fate decisions solely based on membraneless organelles.

2022-05-01 | E-MTAB-8329 | biostudies-arrayexpress

HP1β has distinct subnuclear localizations, chromatin binding features and functions in embryonic stem cells and differentiating cells [ChIP-seq]

Project description:In recent years, several chromatin-related proteins have been shown to regulate ESC pluripotency and/or differentiation, although the role of the major heterochromatin proteins in pluripotency remains largely unknown. Here we identify heterochromatin protein 1-beta (HP1β) to be differentially localized and associated with chromatin in pluripotent and differentiated cells, to be essential for proper ESC differentiation as well as for the maintenance of the pluripotent state. Microscopy analysis supported by biochemical fractionations and chromatin immunoprecipitation (ChIP) experiments demonstrate that unlike its prominent localization in heterochromatic chromocenters in differentiated cells, HP1β is diffuse in the ESC nucleoplasm, poorly bound to chromatin, and highly expressed. The fraction of HP1β that does associate with chromatin in ESCs is highly enriched in genic regions. HP1β-knockout ESCs but not HP1α knockout ESCs exhibit a loss of the morphological and proliferative characteristics of embryonic pluripotent cells. HP1β depletion in ESCs results in reduced expression of pluripotency factors and aberrant differentiation. In contrast, HP1β depletion in differentiated cells perturbs the maintenance of differentiation, and facilitates reprogramming to induced pluripotent stem cells. Our results demonstrate a dual role for HP1β, in ESCs it is essential for pluripotency maintenance, and in differentiated cells for proper differentiation. ChIP-Seq of HP1β in mouse embryonic stem cells.

2015-08-02 | E-GEOD-64946 | biostudies-arrayexpress

HP1β has distinct subnuclear localizations, chromatin binding features and functions in embryonic stem cells and differentiating cells [ChIP-seq]

2015-08-02 | GSE64946 | GEO

Relics of repeat-induced point mutation direct heterochromatin formation in Neurospora crassa

Project description:Both RNAi-dependent and -independent mechanisms have been implicated in the establishment of heterochromatin domains, which may be stabilized by feedback loops involving chromatin proteins and modifications of histones and DNA. Neurospora crassa sports features of heterochromatin found in higher eukaryotes, namely cytosine methylation (5mC), methylation of histone H3 lysine9 (H3K9me) and HETEROCHROMATIN PROTEIN-1 (HP1), and provides a model to investigate heterochromatin establishment and maintenance. We mapped the distribution of HP1, 5mC, H3K9me3 and H3K4me2 at 100bp-resolution and explored their interplay. HP1, H3K9me3 and DNA methylation were extensively colocalized and defined 44 heterochromatic domains on linkage group VII, all relics of repeat-induced point mutation (RIP). Interestingly, the centromere was found in a striking ~350kb heterochromatic domain with no detectable H3K4me2. 5mC was not found in genes, in contrast to the situation in plants and animals. H3K9me3 is required for HP1 localization and DNA methylation. Here, we show that localization of H3K9me3 is independent of 5mC or HP1 at virtually all heterochromatin regions. In addition, we observed complete restoration of DNA methylation patterns after depletion and reintroduction of the H3K9 methylation machinery, indicating that the signals for de novo heterochromatin formation lie upstream of H3K9 methylation. These data show that A:T rich RIPâd DNA efficently directs methylation of H3K9, which in turn, directs methylation of associated cytosines. Immunoprecipitation experiments using antibodies to 5mC, H3K9me3, epitope-tagged HP1, and H3K4me2 were performed. The immunoprecipitate fraction was labeled with Cy5 and the total input was labeled with Cy3. Samples were hybridized to a N. crassa LGVII tiling path microarray.

2010-05-15 | E-GEOD-12690 | biostudies-arrayexpress

Interrogation of the Dynamic Properties of Higher-Order Heterochromatin Using CRISPR/dCas9

Project description:Eukaryotic chromosomes feature large regions of compact, transcriptionally-repressed heterochromatin hallmarked by the presence of Heterochromatin Protein 1 (HP1) family members. HP1 proteins play multi-faceted roles in directly shaping the properties of heterochromatin, and in vivo , HP1 tethering to individual gene promoters leads to epigenetic modifications and gene silencing. However, emergent properties of HP1 at supranucleosomal scales have been difficult to study in cells due to a lack of appropriate tools. Here, we develop CRISPR-Engineered Chromatin Organization (EChO), a novel approach for combining live cell CRISPR-based imaging with inducible and reversible large-scale recruitment of heterochromatin components to native chromatin in human cells. Using CRISPR-EChO, we demonstrate that human HP1α binding across tens of kilobases of genomic DNA leads to formation of novel contacts with other heterochromatin regions and reversibly compacts chromatin from a diffuse to condensed state. The condensed chromatin state exhibits delayed disassembly kinetics and represses transcription across over 600 kilobases. Collectively, these findings support a polymer model of HP1α-mediated chromatin regulation and highlight the utility of CRISPR-EChO in studying and manipulating supranucleosomal chromatin organization in living cells.

2021-05-26 | GSE175500 | GEO

Genome-wide binding profiles of HP1a and Prospero in Drosophila central brain neural precursors and neurons

Project description:Compacted heterochromatin blocks are prevalent in differentiated cells and present a barrier to cellular reprogramming. It remains obscure how heterochromatin remodeling is orchestrated during cell differentiation. Here we find that the evolutionarily conserved homeodomain transcription factor Prospero (Pros)/Prox1 ensures neuronal differentiation by driving heterochromatin domain condensation and expansion. Intriguingly, in mitotically dividing Drosophila neural precursors, Pros is retained at H3K9me3+ pericentromeric heterochromatin regions of chromosomes via liquid-liquid phase separation (LLPS). During mitotic exit of neural precursors, mitotically retained Pros recruits and concentrates heterochromatin protein 1 (HP1) into phase-separated condensates and drives heterochromatin compaction. This establishes a transcriptionally repressive chromatin environment that guarantees cell-cycle exit and terminal neuronal differentiation. Importantly, mammalian Prox1 employs a similar “mitotic-implantation-ensured heterochromatin condensation” strategy to reinforce neuronal differentiation. Together, our results unveiled a new paradigm whereby mitotic implantation of a transcription factor via LLPS remodels H3K9me3+ heterochromatin and drives timely and irreversible terminal differentiation.

2019-12-21 | GSE136413 | GEO

Loss of H3K9me3 heterochromatin at protein coding genes enables developmental lineage specification (ChIP-Seq)

Project description:Domains of transcriptionally repressed heterochromatin, decorated by histone 3 lysine 9 trimethylation (H3K9me3), are reduced in embryonic stem cells compared to fully differentiated cells. However, the establishment and dynamics of closed regions of chromatin at protein coding genes, in natural embryologic development, has not been described. We developed a novel, antibody-independent method to isolate and map compacted heterochromatin from low cell number samples. Unexpectedly, we uncovered extensive high levels of H3K9me3-decorated, compacted heterochromatin at protein coding genes in early, uncommitted cells in the three germ layers, undergoing profound rearrangements and reduction upon differentiation, concomitant with cell type-specific gene expression. Perturbation of the three H3K9me3-related methyltransferases revealed that H3K9me3 heterochromatin is required to maintain cell lineage fidelity. We propose a key role for chromatin-based restriction of gene activity via H3K9me3 during embryologic development

2018-10-31 | GSE114196 | GEO

Loss of H3K9me3 heterochromatin at protein coding genes enables developmental lineage specification (RNA-Seq)

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Loss of H3K9me3 heterochromatin at protein coding genes enables developmental lineage specification (srHC-seq)

2018-10-31 | GSE114197 | GEO

Heterochromatin diversity modulates genome compartmentalization and loop extrusion barriers [Protect-seq]

Project description:Two dominant processes organizing chromosomes are loop extrusion and the compartmental segregation of active and inactive chromatin. The molecular players involved in loop extrusion during interphase, cohesin and CTCF, have been extensively studied and experimentally validated. However, neither the molecular determinants nor the functional roles of compartmentalization are well understood. Here, we distinguish three inactive chromatin states using contact frequency profiling, comprising two types of heterochromatin and a previously uncharacterized inactive state exhibiting a neutral interaction preference. We find that heterochromatin marked by long continuous stretches of H3K9me3, HP1α and HP1β correlates with a conserved signature of strong compartmentalization and is abundant in HCT116 colon cancer cells. We demonstrate that disruption of DNA methyltransferase activity dramatically remodels genome compartmentalization as a consequence of the loss of H3K9me3 and HP1 binding. Interestingly, H3K9me3-HP1α/β is replaced by the neutral inactive state and retains late replication timing. Furthermore, we show that H3K9me3-HP1α/β heterochromatin is permissive to loop extrusion by cohesin but refractory to CTCF, explaining a paucity of visible loop extrusion-associated patterns in Hi-C. Accordingly, CTCF loop extrusion barriers are reactivated upon loss of H3K9me3-HP1α/β, not as a result of canonical demethylation of the CTCF binding motif but due to an intrinsic resistance of H3K9me3-HP1α/β heterochromatin to CTCF binding. Together, our work reveals a dynamic structural and organizational diversity of the inactive portion of the genome and establishes new connections between the regulation of chromatin state and chromosome organization, including an interplay between DNA methylation, compartmentalization and loop extrusion.

2022-07-01 | GSE182106 | GEO

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