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Nicole J Francis - One of the best experts on this subject based on the ideXlab platform.
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phase separation by the polyhomeotic sterile alpha motif compartmentalizes polycomb group Proteins and enhances their activity
Nature Communications, 2020Co-Authors: Elias Seif, Chongwoo A Kim, Jin Joo Kang, Charles Sasseville, Olga Senkovich, Alexander Kaltashov, Elodie Boulier, Ibani Kapur, Nicole J FrancisAbstract:Polycomb Group (PcG) Proteins organize chromatin at multiple scales to regulate gene expression. A conserved Sterile Alpha Motif (SAM) in the Polycomb Repressive Complex 1 (PRC1) subunit Polyhomeotic (Ph) has been shown to play an important role in chromatin compaction and large-scale chromatin organization. Ph SAM forms helical head to tail polymers, and SAM-SAM interactions between chromatin-bound Ph/PRC1 are believed to compact chromatin and mediate long-range interactions. To understand the underlying mechanism, here we analyze the effects of Ph SAM on chromatin in vitro. We find that incubation of chromatin or DNA with a truncated Ph protein containing the SAM results in formation of concentrated, phase-separated condensates. Ph SAM-dependent condensates can recruit PRC1 from extracts and enhance PRC1 ubiquitin ligase activity towards histone H2A. We show that overexpression of Ph with an intact SAM increases ubiquitylated H2A in cells. Thus, SAM-induced phase separation, in the context of Ph, can mediate large-scale compaction of chromatin into biochemical compartments that facilitate histone modification.
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phase separation by the sterile alpha motif of polyhomeotic compartmentalizes polycomb group Proteins and enhances their activity
bioRxiv, 2020Co-Authors: Elias Seif, Chongwoo A Kim, Jin Joo Kang, Charles Sasseville, Alexander Kaltashov, Elodie Boulier, Ibani Kapur, Nicole J Francis, Olga SenkovitchAbstract:Abstract Polycomb Group (PcG) Proteins organize chromatin at multiple scales to regulate gene expression. A conserved Sterile Alpha Motif (SAM) in the Polycomb Repressive Complex 1 (PRC1) subunit Polyhomeotic (Ph) is important for chromatin compaction and large-scale chromatin organization. Like many SAMs, Ph SAM forms helical head to tail polymers, and SAM-SAM interactions between chromatin-bound Ph/PRC1 are believed to compact chromatin and mediate long-range interactions. To understand mechanistically how this occurs, we analyzed the effects of Ph SAM on chromatin in vitro. We find that incubation of chromatin or DNA with a truncated Ph protein containing the SAM results in formation of concentrated, phase-separated condensates. Condensate formation depends on Ph SAM, and is enhanced by but not strictly dependent on, its polymerization activity. Ph SAM-dependent condensates can recruit PRC1 from extracts and enhance PRC1 ubiquitin ligase activity towards histone H2A. Overexpression of Ph with an intact SAM increases ubiquitylated H2A in cells. Thus, phase separation is an activity of the SAM, which, in the context of Ph, can mediate large-scale compaction of chromatin into biochemical compartments that facilitate histone modification.
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Does maintenance of polycomb group Proteins through DNA replication contribute to epigenetic inheritance
Epigenetics, 2009Co-Authors: Nicole J FrancisAbstract:Epigenetic mechanisms maintain transcriptional programs through development and differentiation. One class of epigenetic mechanisms is believed to involve assembly of heritable chromatin features at target genes. These mechanisms require that chromatin structures can be propagated through DNA replication, but little is known about how chromatin structures can be maintained during or reformed after DNA replication. Polycomb Group Proteins maintain transcriptional repression using chromatin-based epigenetic mechanisms. Our recent work suggests that some of these Proteins can be inherited through DNA replication. This result is discussed in light of general models for maintaining chromatin structures through DNA replication and previous studies of Polycomb Group protein-mediated gene silencing.
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Chromatin compaction by a polycomb group protein complex.
Science (New York N.Y.), 2004Co-Authors: Nicole J Francis, Robert E. Kingston, Christopher L. WoodcockAbstract:Polycomb group Proteins preserve body patterning through development by maintaining transcriptional silencing of homeotic genes. A long-standing hypothesis is that silencing involves creating chromatin structure that is repressive to gene transcription. We demonstrate by electron microscopy that core components of Polycomb Repressive Complex 1 induce compaction of defined nucleosomal arrays. Compaction by Polycomb Proteins requires nucleosomes but not histone tails. Each Polycomb complex can compact about three nucleosomes. A region of Posterior Sex Combs that is important for gene silencing in vivo is also important for chromatin compaction, linking the two activities. This mechanism of chromatin compaction might be central to stable gene silencing by the Polycomb group.
Arie P Otte - One of the best experts on this subject based on the ideXlab platform.
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polycomb group Proteins ring1a b are functionally linked to the core transcriptional regulatory circuitry to maintain es cell identity
Development, 2008Co-Authors: Mitsuhiro Endoh, Arie P Otte, Takaho A Endo, Tamie Endoh, Yuichi Fujimura, Osamu Ohara, Tetsuro Toyoda, Masaki Okano, Neil Brockdorff, Miguel VidalAbstract:The Polycomb group (PcG) Proteins mediate heritable silencing of developmental regulators in metazoans, participating in one of two distinct multimeric protein complexes, the Polycomb repressive complexes 1 (PRC1) and 2 (PRC2). Although PRC2 has been shown to share target genes with the core transcription network, including Oct3/4, to maintain embryonic stem (ES) cells, it is still unclear whether PcG Proteins and the core transcription network are functionally linked. Here, we identify an essential role for the core PRC1 components Ring1A/B in repressing developmental regulators in mouse ES cells and, thereby, in maintaining ES cell identity. A significant proportion of the PRC1 target genes are also repressed by Oct3/4. We demonstrate that engagement of PRC1 at target genes is Oct3/4-dependent, whereas engagement of Oct3/4 is PRC1-independent. Moreover, upon differentiation induced by Gata6 expression, most of the Ring1A/B target genes are derepressed and the binding of Ring1A/B to their target loci is also decreased. Collectively, these results indicate that Ring1A/B-mediated Polycomb silencing functions downstream of the core transcriptional regulatory circuitry to maintain ES cell identity.
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polycomb group Proteins ring1a b are functionally linked to the core transcriptional regulatory circuitry to maintain es cell identity
Journal of Cell Science, 2008Co-Authors: Mitsuhiro Endoh, Arie P Otte, Takaho A Endo, Tamie Endoh, Yuichi Fujimura, Osamu Ohara, Tetsuro Toyoda, Masaki Okano, Neil Brockdorff, Miguel VidalAbstract:1. Endoh et al., 2008 Development; doi:10.1242/dev.014340 [OpenUrl][1][Abstract/FREE Full Text][2] [1]: {openurl}?query=rft.jtitle%253DDevelopment%26rft_id%253Dinfo%253Adoi%252F10.1242%252Fdev.014340%26rft_id%253Dinfo%253Apmid%252F18339675%26rft.genre%253Darticle%26rft_val_fmt%253Dinfo%
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polycomb group Proteins ring1a b link ubiquitylation of histone h2a to heritable gene silencing and x inactivation
Developmental Cell, 2004Co-Authors: Mariana De Napoles, Arie P Otte, Jacqueline E Mermoud, Rika Wakao, Amy Y Tang, Mitusuhiro Endoh, Ruth Appanah, Tatyana B Nesterova, Jose C R Silva, Miguel VidalAbstract:Abstract In many higher organisms, 5%–15% of histone H2A is ubiquitylated at lysine 119 (uH2A). The function of this modification and the factors involved in its establishment, however, are unknown. Here we demonstrate that uH2A occurs on the inactive X chromosome in female mammals and that this correlates with recruitment of Polycomb group (PcG) Proteins belonging to Polycomb repressor complex 1 (PRC1). Based on our observations, we tested the role of the PRC1 protein Ring1B and its closely related homolog Ring1A in H2A ubiquitylation. Analysis of Ring1B null embryonic stem (ES) cells revealed extensive depletion of global uH2A levels. On the inactive X chromosome, uH2A was maintained in Ring1A or Ring1B null cells, but not in double knockout cells, demonstrating an overlapping function for these Proteins in development. These observations link H2A ubiquitylation, X inactivation, and PRC1 PcG function, suggesting an unanticipated and novel mechanism for chromatin-mediated heritable gene silencing.
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mitotically stable association of polycomb group Proteins eed and enx1 with the inactive x chromosome in trophoblast stem cells
Current Biology, 2002Co-Authors: Winifred Mak, Arie P Otte, Jose C R Silva, Jonathon Baxter, Alistair E T Newall, Neil BrockdorffAbstract:X inactivation in female mammals is one of the best studied examples of heritable gene silencing and provides an important model for studying maintenance of patterns of gene expression during differentiation and development. The process is initiated by a cis-acting RNA, the X inactive specific transcript (Xist). Xist RNA is thought to recruit silencing complexes to the inactive X, which then serve to establish and maintain the inactive state in all subsequent cell divisions. Most lineages undergo random X inactivation, there being an equal probability of either the maternally (Xm) or paternally (Xp) inherited X chromosome being inactivated in a given cell. In the extraembryonic trophectoderm and primitive endoderm lineages of mouse embryos, however, there is imprinted X inactivation of Xp. This process is also Xist dependent. A recent study has shown that imprinted X inactivation in trophectoderm is not maintained in embryonic ectoderm development (eed) mutant mice. Here we show that Eed and a second Polycomb group protein, Enx1, are directly localized to the inactive X chromosome in XX trophoblast stem (TS) cells. The association of Eed/Enx1 complexes is mitotically stable, suggesting a mechanism for the maintenance of imprinted X inactivation in these cells.
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Differential expression of human Polycomb group Proteins in various tissues and cell types
Journal of Cellular Biochemistry, 2001Co-Authors: M J Gunster, Karien M Hamer, Jan Den L Blaauwen, Frank M. Raaphorst, Elly Fieret, Chris J.l.m. Meijer, Arie P OtteAbstract:Polycomb group Proteins are involved in the maintenance of cellular identity. As multimeric complexes they repress cell type-specific sets of target genes. One model predicts that the composition of Polycomb group complexes determines the specificity for their target genes. To study this hypothesis, we analyzed the expression of Polycomb group genes in various human tissues using Northern blotting and immunohistochemistry. We found that Polycomb group expression varies greatly among tissues and even among specific cell types within a particular tissue. Variations in mRNA expression ranged from expression of all analyzed Polycomb group genes in the heart and testis to no detectable Polycomb group expression at all in bone marrow. Furthermore, each Polycomb group gene was expressed in a different number of tissues. RING1 was expressed in practically all tissues, while HPH1 was expressed in only a few tissues. Also within one tissue the level of Polycomb group expression varied greatly. Cell type-specific Polycomb group expression patterns were observed in thyroid, pancreas, and kidney. Finally, in various developmental stages of fetal kidney, different Polycomb group expression patterns were observed. We conclude that Polycomb group expression can vary depending on the tissue, cell type, and development stage. Polycomb group complexes can only be composed of the Polycomb group Proteins that are expressed. This implies that with cell type-specific Polycomb group expression patterns, cell type-specific Polycomb group complexes exist. The fact that there are cell type-specific Polycomb group targets and cell type-specific Polycomb group complexes fits well with the hypothesis that the composition of Polycomb group complexes may determine their target specificity. J. Cell. Biochem. Suppl. 36: 129-143, 2001.
Peter J Harte - One of the best experts on this subject based on the ideXlab platform.
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Polycomb group Proteins ESC and E(Z) are present in multiple distinct complexes that undergo dynamic changes during development.
Genesis, 2003Co-Authors: Takehito Furuyama, Peter J HarteAbstract:Summary: The Polycomb Group Proteins are required for stable long-term maintenance of transcriptionally repressed states. Two distinct Polycomb Group complexes have been identified, a 2-MDa PRC1 complex and a 600-kDa complex containing the ESC and E(Z) Proteins together with the histone deacetylase RPD3 and the histone-binding protein p55. We report here that there are at least two embryonic ESC/E(Z) complexes that undergo dynamic changes during development and a third larval E(Z) complex that forms after disappearance of ESC. We have identified a larger embryonic ESC complex containing RPD3 and p55, along with E(Z), that is present only until mid-embryogenesis, while the previously identified 600-kDa ESC/E(Z) complex persists until the end of embryogenesis. Constitutive overexpression of ESC does not promote abnormal persistence of the larger or smaller embryonic complexes and does not delay a dissociation of E(Z) from the smaller ESC complex or delay appearance of the larval E(Z) complex, indicating that these changes are developmentally programmed and not regulated by the temporal profile of ESC itself. Genetic removal of ESC prevents appearance of E(Z) in the smaller embryonic complex, but does not appear to affect formation of the large embryonic ESC complex or the PRC1 complex. We also show that the ESC complex is already bound to chromosomes in preblastoderm embryos and present genetic evidence that ESC is required during this very early period. genesis 35:114–124, 2003. © 2003 Wiley-Liss, Inc.
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Polycomb group Proteins ESC and E(Z) are present in multiple distinct complexes that undergo dynamic changes during development.
Genesis (New York N.Y. : 2000), 2003Co-Authors: Takehito Furuyama, Feng Tie, Peter J HarteAbstract:The Polycomb Group Proteins are required for stable long-term maintenance of transcriptionally repressed states. Two distinct Polycomb Group complexes have been identified, a 2-MDa PRC1 complex and a 600-kDa complex containing the ESC and E(Z) Proteins together with the histone deacetylase RPD3 and the histone-binding protein p55. We report here that there are at least two embryonic ESC/E(Z) complexes that undergo dynamic changes during development and a third larval E(Z) complex that forms after disappearance of ESC. We have identified a larger embryonic ESC complex containing RPD3 and p55, along with E(Z), that is present only until mid-embryogenesis, while the previously identified 600-kDa ESC/E(Z) complex persists until the end of embryogenesis. Constitutive overexpression of ESC does not promote abnormal persistence of the larger or smaller embryonic complexes and does not delay a dissociation of E(Z) from the smaller ESC complex or delay appearance of the larval E(Z) complex, indicating that these changes are developmentally programmed and not regulated by the temporal profile of ESC itself. Genetic removal of ESC prevents appearance of E(Z) in the smaller embryonic complex, but does not appear to affect formation of the large embryonic ESC complex or the PRC1 complex. We also show that the ESC complex is already bound to chromosomes in preblastoderm embryos and present genetic evidence that ESC is required during this very early period.
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The Drosophila Polycomb Group Proteins ESC and E(Z) bind directly to each other and co-localize at multiple chromosomal sites
Development (Cambridge England), 1998Co-Authors: Feng Tie, Takehito Furuyama, Peter J HarteAbstract:The Polycomb Group gene esc encodes an evolutionarily conserved protein required for transcriptional silencing of the homeotic genes. Unlike other Polycomb Group genes, esc is expressed and apparently required only during early embryogenesis, suggesting it is required for the initial establishment of silencing but not for its subsequent maintenance. We present evidence that the ESC protein interacts directly with E(Z), another Polycomb Group protein required for silencing of the homeotic genes. We show that the most highly conserved region of ESC, containing seven WD motifs that are predicted to fold into a beta-propeller structure, mediate its binding to a conserved N-terminal region of E(Z). Mutations in the WD region that perturb ESC silencing function in vivo also perturb binding to E(Z) in vitro. The entire WD region forms a trypsin-resistant structure, like known beta -propeller domains, and mutations that would affect the predicted ESC beta-propeller perturb its trypsin-resistance, while a putative structure-conserving mutation does not. We show by co-immunoprecipitation that ESC and E(Z) are directly associated in vivo and that they also co-localize at many chromosomal binding sites. Since E(Z) is required for binding of other Polycomb Group Proteins to chromosomes, these results suggest that formation of an E(Z):ESC complex at Polycomb Response Elements may be an essential prerequisite for the establishment of silencing.
Miguel Vidal - One of the best experts on this subject based on the ideXlab platform.
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polycomb group Proteins ring1a b are functionally linked to the core transcriptional regulatory circuitry to maintain es cell identity
Journal of Cell Science, 2008Co-Authors: Mitsuhiro Endoh, Arie P Otte, Takaho A Endo, Tamie Endoh, Yuichi Fujimura, Osamu Ohara, Tetsuro Toyoda, Masaki Okano, Neil Brockdorff, Miguel VidalAbstract:1. Endoh et al., 2008 Development; doi:10.1242/dev.014340 [OpenUrl][1][Abstract/FREE Full Text][2] [1]: {openurl}?query=rft.jtitle%253DDevelopment%26rft_id%253Dinfo%253Adoi%252F10.1242%252Fdev.014340%26rft_id%253Dinfo%253Apmid%252F18339675%26rft.genre%253Darticle%26rft_val_fmt%253Dinfo%
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polycomb group Proteins ring1a b are functionally linked to the core transcriptional regulatory circuitry to maintain es cell identity
Development, 2008Co-Authors: Mitsuhiro Endoh, Arie P Otte, Takaho A Endo, Tamie Endoh, Yuichi Fujimura, Osamu Ohara, Tetsuro Toyoda, Masaki Okano, Neil Brockdorff, Miguel VidalAbstract:The Polycomb group (PcG) Proteins mediate heritable silencing of developmental regulators in metazoans, participating in one of two distinct multimeric protein complexes, the Polycomb repressive complexes 1 (PRC1) and 2 (PRC2). Although PRC2 has been shown to share target genes with the core transcription network, including Oct3/4, to maintain embryonic stem (ES) cells, it is still unclear whether PcG Proteins and the core transcription network are functionally linked. Here, we identify an essential role for the core PRC1 components Ring1A/B in repressing developmental regulators in mouse ES cells and, thereby, in maintaining ES cell identity. A significant proportion of the PRC1 target genes are also repressed by Oct3/4. We demonstrate that engagement of PRC1 at target genes is Oct3/4-dependent, whereas engagement of Oct3/4 is PRC1-independent. Moreover, upon differentiation induced by Gata6 expression, most of the Ring1A/B target genes are derepressed and the binding of Ring1A/B to their target loci is also decreased. Collectively, these results indicate that Ring1A/B-mediated Polycomb silencing functions downstream of the core transcriptional regulatory circuitry to maintain ES cell identity.
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polycomb group Proteins ring1a b link ubiquitylation of histone h2a to heritable gene silencing and x inactivation
Developmental Cell, 2004Co-Authors: Mariana De Napoles, Arie P Otte, Jacqueline E Mermoud, Rika Wakao, Amy Y Tang, Mitusuhiro Endoh, Ruth Appanah, Tatyana B Nesterova, Jose C R Silva, Miguel VidalAbstract:Abstract In many higher organisms, 5%–15% of histone H2A is ubiquitylated at lysine 119 (uH2A). The function of this modification and the factors involved in its establishment, however, are unknown. Here we demonstrate that uH2A occurs on the inactive X chromosome in female mammals and that this correlates with recruitment of Polycomb group (PcG) Proteins belonging to Polycomb repressor complex 1 (PRC1). Based on our observations, we tested the role of the PRC1 protein Ring1B and its closely related homolog Ring1A in H2A ubiquitylation. Analysis of Ring1B null embryonic stem (ES) cells revealed extensive depletion of global uH2A levels. On the inactive X chromosome, uH2A was maintained in Ring1A or Ring1B null cells, but not in double knockout cells, demonstrating an overlapping function for these Proteins in development. These observations link H2A ubiquitylation, X inactivation, and PRC1 PcG function, suggesting an unanticipated and novel mechanism for chromatin-mediated heritable gene silencing.
Claudia Köhler - One of the best experts on this subject based on the ideXlab platform.
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A fruitful chromatin harvest
Epigenetics, 2012Co-Authors: Nicole Houba-hérin, Lars Hennig, Claudia Köhler, Valerie GaudinAbstract:In September 2011, the Second European Workshop on Plant Chromatin took place in Versailles, France. The workshop covered a range of topics related to plant chromatin biology, including regulation of gene expression by Polycomb group Proteins, chromatin dynamics, reconfiguration of epigenetic marks in response to various cues and chromatin assembly. Here, we summarize some of the highlights discussed during the meeting.
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polycomb group Proteins are required to couple seed coat initiation to fertilization
Proceedings of the National Academy of Sciences of the United States of America, 2011Co-Authors: Pawel Roszak, Claudia KöhlerAbstract:Seed development in flowering plants is initiated after a double fertilization event leading to the formation of zygotic embryo and endosperm tissues surrounded by the maternally derived seed coat. Although the seed coat does not take part in the fertilization process it develops immediately after fertilization, implicating a signaling mechanism from zygotic tissues to the surrounding maternal tissues. We addressed the question of the underlying mechanisms repressing seed coat development before fertilization and initiating seed coat development after fertilization by analyzing combinations of mutants that initiate seed development in the absence of fertilization. We discovered that seed coat development is actively repressed before fertilization by dosage-sensitive Polycomb group Proteins acting in maternal tissues surrounding the female gametophyte. This repression is relieved after fertilization by a signal that is formed by the sexual endosperm. Fertilization is required for signal formation, as asexually formed endosperm fails to effectively initiate seed coat development in mutants with uncompromised maternal Polycomb group function. Mutants for the MADS-box transcription factor AGL62 initiate embryo and endosperm formation but fail to develop a seed coat, implicating AGL62 expression in the endosperm as a requirement for signal initiation. Together, our results provide evidence that fertilization of the central cell generates a signal that relieves Polycomb group-mediated repression in the surrounding maternal tissues to initiate seed coat formation.
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the chd3 chromatin remodeler pickle and polycomb group Proteins antagonistically regulate meristem activity in the arabidopsis root
The Plant Cell, 2011Co-Authors: Ernst Aichinger, Corina B. R. Villar, Claudia Köhler, Riccardo Di Mambro, Sabrina SabatiniAbstract:The chromatin modifying Polycomb group (PcG) and trithorax group (trxG) Proteins are central regulators of cell identity that maintain a tightly controlled balance between cell proliferation and cell differentiation. The opposing activities of PcG and trxG Proteins ensure the correct expression of specific transcriptional programs at defined developmental stages. Here, we report that the chromatin remodeling factor PICKLE (PKL) and the PcG protein CURLY LEAF (CLF) antagonistically determine root meristem activity. Whereas loss of PKL function caused a decrease in meristematic activity, loss of CLF function increased meristematic activity. Alterations of meristematic activity in pkl and clf mutants were not connected with changes in auxin concentration but correlated with decreased or increased expression of root stem cell and meristem marker genes, respectively. Root stem cell and meristem marker genes are modified by the PcG-mediated trimethylation of histone H3 on lysine 27 (H3K27me3). Decreased expression levels of root stem cell and meristem marker genes in pkl correlated with increased levels of H3K27me3, indicating that root meristem activity is largely controlled by the antagonistic activity of PcG Proteins and PKL.
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CHD3 Proteins and Polycomb Group Proteins Antagonistically Determine Cell Identity in Arabidopsis
PLoS Genetics, 2009Co-Authors: Ernst Aichinger, Corina B. R. Villar, Sara Farrona, José C. Reyes, Lars Hennig, Claudia KöhlerAbstract:Dynamic regulation of chromatin structure is of fundamental importance for modulating genomic activities in higher eukaryotes. The opposing activities of Polycomb group (PcG) and trithorax group (trxG) Proteins are part of a chromatinbased cellular memory system ensuring the correct expression of specific transcriptional programs at defined developmental stages. The default silencing activity of PcG Proteins is counteracted by trxG Proteins that activate PcG target genes and prevent PcG mediated silencing activities. Therefore, the timely expression and regulation of PcG Proteins and counteracting trxG Proteins is likely to be of fundamental importance for establishing cell identity. Here, we report that the chromodomain/helicase/DNA‐binding domain CHD3 Proteins PICKLE (PKL) and PICKLE RELATED2 (PKR2) have trxG-like functions in plants and are required for the expression of many genes that are repressed by PcG Proteins. The pkl mutant could partly suppress the leaf and flower phenotype of the PcG mutant curly leaf, supporting the idea that CHD3 Proteins and PcG Proteins antagonistically determine cell identity in plants. The direct targets of PKL in roots include the PcG genes SWINGER and EMBRYONIC FLOWER2 that encode subunits of Polycomb repressive complexes responsible for trimethylating histone H3 at lysine 27 (H3K27me3). Similar to mutants lacking PcG Proteins, lack of PKL and PKR2 caused reduced H3K27me3 levels and, therefore, increased expression of a set of PcG protein target genes in roots. Thus, PKL and PKR2 are directly required for activation of PcG protein target genes and in roots are also indirectly required for repression of PcG protein target genes. Reduced PcG protein activity can lead to cell de-differentiation and callus-like tissue formation in pkl pkr2 mutants. Thus, in contrast to mammals, where PcG Proteins are required to maintain pluripotency and to prevent cell differentiation, in plants PcG Proteins are required to promote cell differentiation by suppressing embryonic development.
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programming of gene expression by polycomb group Proteins
Trends in Cell Biology, 2008Co-Authors: Claudia Köhler, Corina B. R. VillarAbstract:Polycomb group (PcG) complexes maintain epigenetically repressed states that need to be reprogrammed when cells become committed to differentiation. In contrast to the previously held belief that PcG complexes regulate only a few selected genes, recent efforts have revealed hundreds of potential PcG targets in mammals, insects and plants. These results have changed our perception about PcG recruitment and function on chromatin. Both in animals and plants, evolutionarily conserved PcG complexes mark the chromatin of their target genes by methylation at histone H3 lysine 27. Surprisingly, however, both the Proteins recognizing this mark and the mechanisms causing gene repression differ between both kingdoms. This suggests that different developmental strategies used in plant and animal development entailed the evolution of different repressive maintenance mechanisms.