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Akilli N, Cheutin T, Cavalli G. Phase separation and inheritance of repressive chromatin domains. Curr Opin Genet Dev 2024; 86:102201. [PMID: 38701672 DOI: 10.1016/j.gde.2024.102201] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 12/08/2023] [Revised: 04/04/2024] [Accepted: 04/16/2024] [Indexed: 05/05/2024]
Abstract
Polycomb-associated chromatin and pericentromeric heterochromatin form genomic domains important for the epigenetic regulation of gene expression. Both Polycomb complexes and heterochromatin factors rely on 'read and write' mechanisms, which, on their own, are not sufficient to explain the formation and the maintenance of these epigenetic domains. Microscopy has revealed that they form specific nuclear compartments separated from the rest of the genome. Recently, some subunits of these molecular machineries have been shown to undergo phase separation, both in vitro and in vivo, suggesting that phase separation might play important roles in the formation and the function of these two kinds of repressive chromatin. In this review, we will present the recent advances in the field of facultative and constitutive heterochromatin formation and maintenance through phase separation.
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Affiliation(s)
- Nazli Akilli
- Institute of Human Genetics, CNRS, University of Montpellier, Montpellier, France. https://twitter.com/@sinmerank
| | - Thierry Cheutin
- Institute of Human Genetics, CNRS, University of Montpellier, Montpellier, France
| | - Giacomo Cavalli
- Institute of Human Genetics, CNRS, University of Montpellier, Montpellier, France.
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Uckelmann M, Davidovich C. Chromatin compaction by Polycomb group proteins revisited. Curr Opin Struct Biol 2024; 86:102806. [PMID: 38537534 DOI: 10.1016/j.sbi.2024.102806] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 11/29/2023] [Revised: 02/29/2024] [Accepted: 03/05/2024] [Indexed: 05/19/2024]
Abstract
The chromatin compaction activity of Polycomb group proteins has traditionally been considered essential for transcriptional repression. However, there is very little information on how Polycomb group proteins compact chromatin at the molecular level and no causal link between the compactness of chromatin and transcriptional repression. Recently, a more complete picture of Polycomb-dependent chromatin architecture has started to emerge, owing to advanced methods for imaging and chromosome conformation capture. Discoveries into Polycomb-driven phase separation add another layer of complexity. Recent observations generally imply that Polycomb group proteins modulate chromatin structure at multiple scales to reduce its dynamics and segregate it from active domains. Hence, it is reasonable to hypothesise that Polycomb group proteins maintain the energetically favourable state of compacted chromatin, rather than actively compact it.
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Affiliation(s)
- Michael Uckelmann
- Department of Biochemistry and Molecular Biology, Biomedicine Discovery Institute, Faculty of Medicine, Nursing and Health Sciences, Monash University, Clayton, Victoria, 3800, Australia.
| | - Chen Davidovich
- Department of Biochemistry and Molecular Biology, Biomedicine Discovery Institute, Faculty of Medicine, Nursing and Health Sciences, Monash University, Clayton, Victoria, 3800, Australia; EMBL-Australia, Clayton, Victoria, 3800, Australia.
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Hu M, Yeh YH, Maezawa S, Nakagawa T, Yoshida S, Namekawa S. PRC1 directs PRC2-H3K27me3 deposition to shield adult spermatogonial stem cells from differentiation. Nucleic Acids Res 2024; 52:2306-2322. [PMID: 38142439 PMCID: PMC10954450 DOI: 10.1093/nar/gkad1203] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 09/17/2023] [Revised: 11/16/2023] [Accepted: 12/11/2023] [Indexed: 12/26/2023] Open
Abstract
Spermatogonial stem cells functionality reside in the slow-cycling and heterogeneous undifferentiated spermatogonia cell population. This pool of cells supports lifelong fertility in adult males by balancing self-renewal and differentiation to produce haploid gametes. However, the molecular mechanisms underpinning long-term stemness of undifferentiated spermatogonia during adulthood remain unclear. Here, we discover that an epigenetic regulator, Polycomb repressive complex 1 (PRC1), shields adult undifferentiated spermatogonia from differentiation, maintains slow cycling, and directs commitment to differentiation during steady-state spermatogenesis in adults. We show that PRC2-mediated H3K27me3 is an epigenetic hallmark of adult undifferentiated spermatogonia. Indeed, spermatogonial differentiation is accompanied by a global loss of H3K27me3. Disruption of PRC1 impairs global H3K27me3 deposition, leading to precocious spermatogonial differentiation. Therefore, PRC1 directs PRC2-H3K27me3 deposition to maintain the self-renewing state of undifferentiated spermatogonia. Importantly, in contrast to its role in other tissue stem cells, PRC1 negatively regulates the cell cycle to maintain slow cycling of undifferentiated spermatogonia. Our findings have implications for how epigenetic regulators can be tuned to regulate the stem cell potential, cell cycle and differentiation to ensure lifelong fertility in adult males.
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Affiliation(s)
- Mengwen Hu
- Department of Microbiology and Molecular Genetics, University of California, Davis, Davis, CA 95616, USA
- Division of Reproductive Sciences, Division of Developmental Biology, Perinatal Institute, Cincinnati Children's Hospital Medical Center, Cincinnati, OH 45229, USA
| | - Yu-Han Yeh
- Department of Microbiology and Molecular Genetics, University of California, Davis, Davis, CA 95616, USA
- Division of Reproductive Sciences, Division of Developmental Biology, Perinatal Institute, Cincinnati Children's Hospital Medical Center, Cincinnati, OH 45229, USA
| | - So Maezawa
- Division of Reproductive Sciences, Division of Developmental Biology, Perinatal Institute, Cincinnati Children's Hospital Medical Center, Cincinnati, OH 45229, USA
- Faculty of Science and Technology, Department of Applied Biological Science, Tokyo University of Science, Noda, Chiba 281-8510, Japan
| | - Toshinori Nakagawa
- Division of Germ Cell Biology, National Institute for Basic Biology, National Institutes of Natural Sciences, 5-1 Higashiyama, Myodaiji, Okazaki 444-8787, Japan
- Course for Basic Biology, The Graduate Institute for Advanced Studies, SOKENDAI, 5-1 Higashiyama, Myodaiji, Okazaki 444-8787, Japan
| | - Shosei Yoshida
- Division of Germ Cell Biology, National Institute for Basic Biology, National Institutes of Natural Sciences, 5-1 Higashiyama, Myodaiji, Okazaki 444-8787, Japan
- Course for Basic Biology, The Graduate Institute for Advanced Studies, SOKENDAI, 5-1 Higashiyama, Myodaiji, Okazaki 444-8787, Japan
| | - Satoshi H Namekawa
- Department of Microbiology and Molecular Genetics, University of California, Davis, Davis, CA 95616, USA
- Division of Reproductive Sciences, Division of Developmental Biology, Perinatal Institute, Cincinnati Children's Hospital Medical Center, Cincinnati, OH 45229, USA
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Ingersoll S, Trouth A, Luo X, Espinoza A, Wen J, Tucker J, Astatike K, Phiel CJ, Kutateladze TG, Wu TP, Ramachandran S, Ren X. Sparse CBX2 nucleates many Polycomb proteins to promote facultative heterochromatinization of Polycomb target genes. BIORXIV : THE PREPRINT SERVER FOR BIOLOGY 2024:2024.02.05.578969. [PMID: 38370615 PMCID: PMC10871256 DOI: 10.1101/2024.02.05.578969] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Key Words] [Grants] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 02/20/2024]
Abstract
Facultative heterochromatinization of genomic regulators by Polycomb repressive complex (PRC) 1 and 2 is essential in development and differentiation; however, the underlying molecular mechanisms remain obscure. Using genetic engineering, molecular approaches, and live-cell single-molecule imaging, we quantify the number of proteins within condensates formed through liquid-liquid phase separation (LLPS) and find that in mouse embryonic stem cells (mESCs), approximately 3 CBX2 proteins nucleate many PRC1 and PRC2 subunits to form one non-stoichiometric condensate. We demonstrate that sparse CBX2 prevents Polycomb proteins from migrating to constitutive heterochromatin, demarcates the spatial boundaries of facultative heterochromatin, controls the deposition of H3K27me3, regulates transcription, and impacts cellular differentiation. Furthermore, we show that LLPS of CBX2 is required for the demarcation and deposition of H3K27me3 and is essential for cellular differentiation. Our findings uncover new functional roles of LLPS in the formation of facultative heterochromatin and unravel a new mechanism by which low-abundant proteins nucleate many other proteins to form compartments that enable them to execute their functions.
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Affiliation(s)
- Steven Ingersoll
- Department of Chemistry, University of Colorado Denver, Denver, CO 80217-3364, USA
| | - Abby Trouth
- Department of Biochemistry and Molecular Genetics, University of Colorado School of Medicine, Aurora, CO, USA
| | - Xinlong Luo
- Department of Molecular and Human Genetics, Baylor College of Medicine, Houston, TX, USA
| | - Axel Espinoza
- Department of Integrative Biology, University of Colorado Denver, CO 80217-3364, USA
| | - Joey Wen
- Department of Chemistry, University of Colorado Denver, Denver, CO 80217-3364, USA
| | - Joseph Tucker
- Department of Integrative Biology, University of Colorado Denver, CO 80217-3364, USA
| | - Kalkidan Astatike
- Department of Chemistry, University of Colorado Denver, Denver, CO 80217-3364, USA
| | - Christopher J. Phiel
- Department of Integrative Biology, University of Colorado Denver, CO 80217-3364, USA
| | - Tatiana G. Kutateladze
- Department of Pharmacology, University of Colorado School of Medicine, Aurora, CO 80045, USA
| | - Tao P. Wu
- Department of Molecular and Human Genetics, Baylor College of Medicine, Houston, TX, USA
| | - Srinivas Ramachandran
- Department of Biochemistry and Molecular Genetics, University of Colorado School of Medicine, Aurora, CO, USA
- RNA Bioscience Initiative, University of Colorado School of Medicine, Aurora, CO, USA
| | - Xiaojun Ren
- Department of Chemistry, University of Colorado Denver, Denver, CO 80217-3364, USA
- Department of Integrative Biology, University of Colorado Denver, CO 80217-3364, USA
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