Histone marks enable formation of immiscible phase-separated chromatin compartments
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ABSTRACT:
ORGANISM(S): Mus musculus
PROVIDER: GSE241262 | GEO | 2025/04/07
REPOSITORIES: GEO
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Project description:Polycomb Repressive Complexes 1 and 2 (PRC1 and PRC2) are histone-modifying and -binding complexes that mediate the formation of facultative heterochromatin and are required for silencing of developmental genes and maintenance of cell fate. Multiple pathways of RNA decay work together to establish and maintain heterochromatin in fission yeast, including a recently identified role for a conserved RNA degradation complex called the rixosome or RIX1 complex. Whether RNA degradation also plays a role in the stability of mammalian heterochromatin remains unknown. Here we show that the rixosome contributes to silencing of many Polycomb targets in human cells. The rixosome associates with human PRC complexes and is enriched at promoters of Polycomb target genes. Importantly, depletion of either the rixosome or Polycomb results in accumulation of paused and elongating RNA polymerase at Polycomb-target genes. We identify point mutations in the RING1B subunit of PRC1 that disrupt the interaction between PRC1 and the rixosome and result in diminished silencing, suggesting that direct recruitment of the rixosome to chromatin is required for silencing. Finally, we show that the RNA kinase activity of the rixosome and the XRN2 exoribonuclease, which degrades RNAs with 5’ mono-phosphate groups generated by the rixosome, are required for silencing. Our findings suggest that rixosome-mediated degradation of nascent RNA is conserved from fission yeast to human, although in human cells the rixosome degrades RNA in facultative rather than constitutive heterochromatin.
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Project description:During mitosis, condensin activity is thought to disrupt interphase chromatin structures. Here, we utilize condensin-deficient mitotic chromosomes as a unique architectural platform to further investigate genome folding principles. Upon condensin loss, compartments progressively emerge in mitotic chromosomes. Euchromatin diverges into two different compartments A1 and A2, the former of which shows strong homotypic interactions while the latter exhibit reduced self-aggregation. Constitutive heterochromatin (B1) displays reduced level of compartmentalization and the normally inert facultative heterochromatin (B2) participates to compartmentalize the genome. Dynamically, A1 compartment is established remarkably fast with similarly efficient separation from B1 while reformation of B1 is delayed, implying that A1 self-attraction is the engine to compartmentalizalize the condensin-depleted mitotic chromosomes. Notified by the mitotic compartmentalization of B1 which lacks HP1 binding, we sought to explore the role of HP1 proteins in genome folding and demonstrat that HP1& are dispensible for chromatin structural restoration during cell divison. Our observations unveil delicate patterns and novel principles of genome compartmentalization that are otherwise hidden in interphase cells.
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Project description:During mitosis, condensin activity is thought to disrupt interphase chromatin structures. Here, we utilize condensin-deficient mitotic chromosomes as a unique architectural platform to further investigate genome folding principles. Upon condensin loss, compartments progressively emerge in mitotic chromosomes. Euchromatin diverges into two different compartments A1 and A2, the former of which shows strong homotypic interactions while the latter exhibit reduced self-aggregation. Constitutive heterochromatin (B1) displays reduced level of compartmentalization and the normally inert facultative heterochromatin (B2) participates to compartmentalize the genome. Dynamically, A1 compartment is established remarkably fast with similarly efficient separation from B1 while reformation of B1 is delayed, implying that A1 self-attraction is the engine to compartmentalizalize the condensin-depleted mitotic chromosomes. Notified by the mitotic compartmentalization of B1 which lacks HP1 binding, we sought to explore the role of HP1 proteins in genome folding and demonstrat that HP1& are dispensible for chromatin structural restoration during cell divison. Our observations unveil delicate patterns and novel principles of genome compartmentalization that are otherwise hidden in interphase cells.
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Project description:During mitosis, condensin activity is thought to disrupt interphase chromatin structures. Here, we utilize condensin-deficient mitotic chromosomes as a unique architectural platform to further investigate genome folding principles. Upon condensin loss, compartments progressively emerge in mitotic chromosomes. Euchromatin diverges into two different compartments A1 and A2, the former of which shows strong homotypic interactions while the latter exhibit reduced self-aggregation. Constitutive heterochromatin (B1) displays reduced level of compartmentalization and the normally inert facultative heterochromatin (B2) participates to compartmentalize the genome. Dynamically, A1 compartment is established remarkably fast with similarly efficient separation from B1 while reformation of B1 is delayed, implying that A1 self-attraction is the engine to compartmentalizalize the condensin-depleted mitotic chromosomes. Notified by the mitotic compartmentalization of B1 which lacks HP1 binding, we sought to explore the role of HP1 proteins in genome folding and demonstrat that HP1& are dispensible for chromatin structural restoration during cell divison. Our observations unveil delicate patterns and novel principles of genome compartmentalization that are otherwise hidden in interphase cells.
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Project description:During mitosis, condensin activity is thought to disrupt interphase chromatin structures. Here, we utilize condensin-deficient mitotic chromosomes as a unique architectural platform to further investigate genome folding principles. Upon condensin loss, compartments progressively emerge in mitotic chromosomes. Euchromatin diverges into two different compartments A1 and A2, the former of which shows strong homotypic interactions while the latter exhibit reduced self-aggregation. Constitutive heterochromatin (B1) displays reduced level of compartmentalization and the normally inert facultative heterochromatin (B2) participates to compartmentalize the genome. Dynamically, A1 compartment is established remarkably fast with similarly efficient separation from B1 while reformation of B1 is delayed, implying that A1 self-attraction is the engine to compartmentalizalize the condensin-depleted mitotic chromosomes. Notified by the mitotic compartmentalization of B1 which lacks HP1 binding, we sought to explore the role of HP1 proteins in genome folding and demonstrat that HP1& are dispensible for chromatin structural restoration during cell divison. Our observations unveil delicate patterns and novel principles of genome compartmentalization that are otherwise hidden in interphase cells.
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