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DNA methylation (5-methylcytosine, 5mC) is a repressive gene regulatory mark widespread in vertebrate genomes, yet the developmental dynamics in which 5mC patterns are established vary across species. While mammals undergo two rounds of global 5mC erasure, the zebrafish genome exhibits localized maternal-to-paternal 5mC remodeling, in which the sperm epigenome is inherited in the early embryo. To date, it is unclear how evolutionarily conserved such 5mC remodeling strategies are, and what their biological function is. Here, we studied 5mC dynamics during the embryonic development of sea lamprey (Petromyzon marinus), a jawless vertebrate which occupies a critical phylogenetic position as the sister group of the jawed vertebrates. We employed base-resolution 5mC quantification in the lamprey germline, embryonic and somatic tissues, and discovered large-scale maternal-to-paternal epigenome remodeling that affects >30% of the embryonic genome and is predominantly associated with partially methylated domains (PMDs). We further demonstrate that sequences eliminated during programmed genome rearrangement (PGR), a hallmark of lamprey embryogenesis, are hypermethylated in sperm prior to the onset of PGR. Our study thus unveils important insights into the evolutionary origins of vertebrate 5mC reprogramming, and how this process might participate in diverse developmental strategies.

Precise control of gene expression is fundamental to cell function and development. Although ultimately gene expression relies on DNA-binding transcription factors to guide the activity of the transcription machinery to genes, it has also become clear that chromatin and histone post-translational modification have fundamental roles in gene regulation. Polycomb repressive complexes represent a paradigm of chromatin-based gene regulation in animals. The Polycomb repressive system comprises two central protein complexes, Polycomb repressive complex 1 (PRC1) and PRC2, which are essential for normal gene regulation and development. Our early understanding of Polycomb function relied on studies in simple model organisms, but more recently it has become apparent that this system has expanded and diverged in mammals. Detailed studies are now uncovering the molecular mechanisms that enable mammalian PRC1 and PRC2 to identify their target sites in the genome, communicate through feedback mechanisms to create Polycomb chromatin domains, and control transcription to regulate gene expression. In this Review, we discuss and contextualise the emerging principles that define how this fascinating chromatin-based system regulates gene expression in mammals.

The potential of pluripotent cells to respond to developmental cues and trigger cell differentiation is enhanced during the G1 phase of the cell cycle, but the molecular mechanisms involved are poorly understood. Variations in polycomb activity during interphase progression have been hypothesized to regulate the cell-cycle-phase-dependent transcriptional activation of differentiation genes during lineage transition in pluripotent cells. Here, we asked whether the Polycomb Repressive Complex 1 (PRC1) modulates the ability of mouse embryonic stem cells (ESCs) to differentially respond to developmental cues depending on the phase of the cell cycle in which they are found. We discovered that recruitment of PRC1 complexes and their associated molecular functions, ubiquitination of H2AK119 and three-dimensional chromatin interactions, are enhanced during S and G2 phases compared to the G1 phase. In agreement with the accumulation of PRC1 at target promoters upon G1 phase exit, cells in S and G2 phases show firmer transcriptional repression of developmental regulator genes that is drastically perturbed upon genetic ablation of the PRC1 catalytic subunit Ring1b. Importantly, depletion of Ring1b during retinoic acid stimulation interferes with the preference of mESCs to induce the transcriptional activation of differentiation genes in G1 phase. We propose that incremental enrolment of polycomb repressive activity during interphase progression reduces the tendency of cells to respond to developmental cues during S and G2 phases, facilitating activation of cell differentiation in the G1 phase of the pluripotent cell cycle.

Precise control of gene expression underpins normal development. This relies on mechanisms that enable communication between gene promoters and other regulatory elements. In embryonic stem cells (ESCs), the cyclin-dependent kinase module Mediator complex (CKM–Mediator) has been reported to physically link gene regulatory elements to enable gene expression and also prime genes for induction during differentiation. Here, we show that CKM–Mediator contributes little to three-dimensional genome organization in ESCs, but it has a specific and essential role in controlling interactions between inactive gene regulatory elements bound by Polycomb repressive complexes (PRCs). These interactions are established by the canonical PRC1 (cPRC1) complex but rely on CKM–Mediator, which facilitates binding of cPRC1 to its target sites. Importantly, through separation-of-function experiments, we reveal that this collaboration between CKM–Mediator and cPRC1 in creating long-range interactions does not function to prime genes for induction during differentiation. Instead, we discover that priming relies on an interaction-independent mechanism whereby the CKM supports core Mediator engagement with gene promoters during differentiation to enable gene activation.

The Polycomb repressive system functions through chromatin to regulate gene expression and development. In this issue of Genes & Development, Cohen and colleagues (pp. 354–366) use the developing mouse epidermis as a model system to show that the two central Polycomb repressive complexes, PRC1 and PRC2, have autonomous yet overlapping functions in repressing Polycomb target genes. They show that this cooperation enables the stable repression of nonepidermal transcription factors that would otherwise compromise epidermal cell identity and disrupt normal skin development.

Histone-modifying systems play fundamental roles in gene regulation and the development of multicellular organisms. Histone modifications that are enriched at gene regulatory elements have been heavily studied, but the function of modifications found more broadly throughout the genome remains poorly understood. This is exemplified by histone H2A monoubiquitylation (H2AK119ub1), which is enriched at Polycomb-repressed gene promoters but also covers the genome at lower levels. Here, using inducible genetic perturbations and quantitative genomics, we found that the BAP1 deubiquitylase plays an essential role in constraining H2AK119ub1 throughout the genome. Removal of BAP1 leads to pervasive genome-wide accumulation of H2AK119ub1, which causes widespread reductions in gene expression. We show that elevated H2AK119ub1 preferentially counteracts Ser5 phosphorylation on the C-terminal domain of RNA polymerase II at gene regulatory elements and causes reductions in transcription and transcription-associated histone modifications. Furthermore, failure to constrain pervasive H2AK119ub1 compromises Polycomb complex occupancy at a subset of Polycomb target genes, which leads to their derepression, providing a potential molecular rationale for why the BAP1 ortholog in Drosophila has been characterized as a Polycomb group gene. Together, these observations reveal that the transcriptional potential of the genome can be modulated by regulating the levels of a pervasive histone modification.

The Polycomb repressive system plays a fundamental role in controlling gene expression during mammalian development. To achieve this, Polycomb repressive complexes 1 and 2 (PRC1 and PRC2) bind target genes and use histone modification-dependent feedback mechanisms to form Polycomb chromatin domains and repress transcription. The inter-relatedness of PRC1 and PRC2 activity at these sites has made it difficult to discover the specific components of Polycomb chromatin domains that drive gene repression and to understand mechanistically how this is achieved. Here, by exploiting rapid degron-based approaches and time-resolved genomics, we kinetically dissect Polycomb-mediated repression and discover that PRC1 functions independently of PRC2 to counteract RNA polymerase II binding and transcription initiation. Using single-cell gene expression analysis, we reveal that PRC1 acts uniformly within the cell population and that repression is achieved by controlling transcriptional burst frequency. These important new discoveries provide a mechanistic and conceptual framework for Polycomb-dependent transcriptional control. Here the authors find that Polycomb repressive complex PRC1 functions independently of PRC2 to counteract Pol II binding, regulating transcription initiation and burst frequency.

The precise regulation of gene transcription is required to establish and maintain cell type-specific gene expression programs during multicellular development. In addition to transcription factors, chromatin, and its chemical modification, play a central role in regulating gene expression. In vertebrates, DNA is pervasively methylated at CG dinucleotides, a modification that is repressive to transcription. However, approximately 70% of vertebrate gene promoters are associated with DNA elements called CpG islands (CGIs) that are refractory to DNA methylation. CGIs integrate the activity of a range of chromatin-regulating factors that can post-translationally modify histones and modulate gene expression. This is exemplified by the trimethylation of histone H3 at lysine 4 (H3K4me3), which is enriched at CGI-associated gene promoters and correlates with transcriptional activity. Through studying H3K4me3 at CGIs it has become clear that CGIs shape the distribution of H3K4me3 and, in turn, H3K4me3 influences the chromatin landscape at CGIs. Here we will discuss our understanding of the emerging relationship between CGIs, H3K4me3, and gene expression., Highlights • The deposition of H3K4me3 is intrinsically linked to CpG islands via ZF-CxxC domain-containing proteins. • H3K4me3 levels at CpG islands are regulated by transcription and other chromatin features. • H3K4me3 influences chromatin architecture at CpG islands and has been proposed to regulate gene expression. • H3K4me3 may contribute to bistable chromatin states at CpG islands.

DNA methylation of enhancers is dynamic, cell-type specific, and vital for cell fate progression. However, current models inadequately define its role within the hierarchy of gene regulation. Analysis of independent datasets shows an unanticipated overlap between DNA methylation and chromatin accessibility at enhancers of steady state stem cells, suggesting that these two opposing features might exist concurrently. To define their temporal relationship, we developed ATAC-Me, which probes accessibility and methylation from single DNA library preparations. We identified waves of accessibility occurring rapidly across thousands of myeloid enhancers in a monocyte-to-macrophage cell fate model. Prolonged methylation states were observed at a majority of these sites while transcription of nearby genes tracked closely with accessibility. ATAC-Me uncovers a significant disconnect between chromatin accessibility, DNA methylation status, and gene activity. This unexpected observation highlights the value of ATAC-Me in constructing precise molecular timelines for understanding the role of DNA methylation in gene regulation.

Polycomb repressive complexes-1 and -2 (PRC1 and 2) silence developmental genes in a spatiotemporal manner during embryogenesis. How Polycomb group (PcG) proteins orchestrate down-regulation of target genes upon differentiation, however, remains elusive. Here, by differentiating embryonic stem cells into embryoid bodies, we reveal a crucial role for the PCGF1-containing variant PRC1 complex (PCGF1-PRC1) to mediate differentiation-associated down-regulation of a group of genes. Upon differentiation cues, transcription is down-regulated at these genes, in association with PCGF1-PRC1-mediated deposition of histone H2AK119 mono-ubiquitination (H2AK119ub1) and PRC2 recruitment. In the absence of PCGF1-PRC1, both H2AK119ub1 deposition and PRC2 recruitment are disrupted, leading to aberrant expression of target genes. PCGF1-PRC1 is, therefore, required for initiation and consolidation of PcG-mediated gene repression during differentiation. Polycomb repressive complexes (PRC1 and PRC2) repress genes that are crucial for development via epigenetic modifications; however, their role in differentiation is not well known. Here the authors reveal that a PCGF1-containing PRC1 variant facilitates exit from pluripotency by downregulating target genes and recruiting PRC2.

Epigenetic modifications on chromatin play important roles in regulating gene expression. While chromatin states are often governed by multi-layered structure, how individual pathways contribute to gene expression remains poorly understood. For example, DNA methylation is known to regulate transcription factor binding but also to recruit methyl-CpG binding proteins that affect chromatin structure through the activity of histone deacetylase complexes (HDACs). Both of these mechanisms can potentially affect gene expression, but the importance of each, and whether these activities are integrated to achieve appropriate gene regulation, remains largely unknown. To address this important question, we measured gene expression, chromatin accessibility, and transcription factor occupancy in wild-type or DNA methylation-deficient mouse embryonic stem cells following HDAC inhibition. Interestingly, we observe widespread increases in chromatin accessibility at repeat elements when HDACs are inhibited, and this is magnified when cells also lack DNA methylation. A subset of these elements have elevated binding of the YY1 and GABPA transcription factors and increased expression. The pronounced additive effect of HDAC inhibition in DNA methylation deficient cells demonstrate that DNA methylation and histone deacetylation act largely independently to suppress transcription factor binding and gene expression.

Somatic cell nuclear transfer (SCNT) can reprogram a somatic nucleus to a totipotent state. However, the re-organization of 3D chromatin structure in this process remains poorly understood. Using low-input Hi-C, we revealed that, during SCNT, the transferred nucleus first enters a mitotic-like state (premature chromatin condensation). Unlike fertilized embryos, SCNT embryos show stronger topologically associating domains (TADs) at the 1-cell stage. TADs become weaker at the 2-cell stage, followed by gradual consolidation. Compartments A/B are markedly weak in 1-cell SCNT embryos and become increasingly strengthened afterward. By the 8-cell stage, somatic chromatin architecture is largely reset to embryonic patterns. Unexpectedly, we found cohesin represses minor zygotic genome activation (ZGA) genes (2-cell-specific genes) in pluripotent and differentiated cells, and pre-depleting cohesin in donor cells facilitates minor ZGA and SCNT. These data reveal multi-step reprogramming of 3D chromatin architecture during SCNT and support dual roles of cohesin in TAD formation and minor ZGA repression.

Summary How chromosome organization is related to genome function remains poorly understood. Cohesin, loop extrusion, and CCCTC-binding factor (CTCF) have been proposed to create topologically associating domains (TADs) to regulate gene expression. Here, we examine chromosome conformation in embryonic stem cells lacking cohesin and find, as in other cell types, that cohesin is required to create TADs and regulate A/B compartmentalization. However, in the absence of cohesin, we identify a series of long-range chromosomal interactions that persist. These correspond to regions of the genome occupied by the polycomb repressive system and are dependent on PRC1. Importantly, we discover that cohesin counteracts these polycomb-dependent interactions, but not interactions between super-enhancers. This disruptive activity is independent of CTCF and insulation and appears to modulate gene repression by the polycomb system. Therefore, we discover that cohesin disrupts polycomb-dependent chromosome interactions to modulate gene expression in embryonic stem cells., Graphical Abstract, Highlights • Interaction between polycomb target genes in ESCs occurs independently of cohesin • Loop extrusion by cohesin disrupts interactions between polycomb target genes • Cohesin removal enhances repression at polycomb target genes with increased interactions, Using Hi-C, Capture-C, and DNA-FISH, Rhodes et al. discover that interactions between polycomb target genes occur independently of cohesin in embryonic stem cells. This relies on PRC1, and these interactions are disrupted by cohesin-mediated loop extrusion. Upon removal of cohesin, gene repression is enhanced at polycomb-occupied genes with increased interactions.

CpG islands are gene regulatory elements associated with the majority of mammalian promoters, yet how they regulate gene expression remains poorly understood. Here, we identify FBXL19 as a CpG island-binding protein in mouse embryonic stem (ES) cells and show that it associates with the CDK-Mediator complex. We discover that FBXL19 recruits CDK-Mediator to CpG island-associated promoters of non-transcribed developmental genes to prime these genes for activation during cell lineage commitment. We further show that recognition of CpG islands by FBXL19 is essential for mouse development. Together this reveals a new CpG island-centric mechanism for CDK-Mediator recruitment to developmental gene promoters in ES cells and a requirement for CDK-Mediator in priming these developmental genes for activation during cell lineage commitment.

Polycomb group (PcG) proteins are transcriptional repressors that play important roles in regulating gene expression during animal development. In vitro experiments have shown that PcG protein complexes can compact chromatin to limit the activity of chromatin remodeling enzymes and access of the transcriptional machinery to DNA. In fitting with these ideas, gene promoters associated with PcG proteins have been reported to be less accessible than other gene promoters. However, it remains largely untested in vivo whether PcG proteins define chromatin accessibility or other chromatin features. To address this important question, we examine the chromatin accessibility and nucleosome landscape at PcG protein-bound promoters in mouse embryonic stem cells using the assay for transposase accessible chromatin (ATAC)-seq. Combined with genetic ablation strategies, we unexpectedly discover that although PcG protein-occupied gene promoters exhibit reduced accessibility, this does not rely on PcG proteins. Instead, the Polycomb repressive complex 1 (PRC1) appears to play a unique role in driving elevated nucleosome occupancy and decreased nucleosomal spacing in Polycomb chromatin domains. Our new genome-scale observations argue, in contrast to the prevailing view, that PcG proteins do not significantly affect chromatin accessibility and highlight an underappreciated complexity in the relationship between chromatin accessibility, the nucleosome landscape, and PcG-mediated transcriptional repression.

CpG islands are regions of vertebrate genomes that often function as gene regulatory elements and are associated with most gene promoters. CpG island elements usually contain nonmethylated CpG dinucleotides, while the remainder of the genome is pervasively methylated. We developed a biochemical approach called biotinylated CxxC affinity purification (BioCAP) to unbiasedly isolate regions of the genome that contain nonmethylated CpG dinucleotides. The resulting highly pure nonmethylated DNA is easily analyzed by quantitative PCR to interrogate specific loci or via massively parallel sequencing to yield genome-wide profiles.

The ring finger protein PCGF6 (polycomb group ring finger 6) interacts with RING1A/B and E2F6 associated factors to form a non-canonical PRC1 (polycomb repressive complex 1) known as PCGF6-PRC1. Here, we demonstrate that PCGF6-PRC1 plays a role in repressing a subset of PRC1 target genes by recruiting RING1B and mediating downstream mono-ubiquitination of histone H2A. PCGF6-PRC1 bound loci are highly enriched for promoters of germ cell-related genes in mouse embryonic stem cells (ESCs). Conditional ablation of Pcgf6 in ESCs leads to robust de-repression of such germ cell-related genes, in turn affecting cell growth and viability. We also find a role for PCGF6 in pre- and peri-implantation mouse embryonic development. We further show that a heterodimer of the transcription factors MAX and MGA recruits PCGF6 to target loci. PCGF6 thus links sequence specific target recognition by the MAX/MGA complex to PRC1-dependent transcriptional silencing of germ cell-specific genes in pluripotent stem cells. DOI: http://dx.doi.org/10.7554/eLife.21064.001

Polycomb group (PcG) proteins function as chromatin-based transcriptional repressors that are essential for normal gene regulation during development. However, how these systems function to achieve transcriptional regulation remains very poorly understood. Here, we discover that the histone H2AK119 E3 ubiquitin ligase activity of Polycomb repressive complex 1 (PRC1) is defined by the composition of its catalytic subunits and is highly regulated by RYBP/YAF2-dependent stimulation. In mouse embryonic stem cells, RYBP plays a central role in shaping H2AK119 mono-ubiquitylation at PcG targets and underpins an activity-based communication between PRC1 and Polycomb repressive complex 2 (PRC2) which is required for normal histone H3 lysine 27 trimethylation (H3K27me3). Without normal histone modification-dependent communication between PRC1 and PRC2, repressive Polycomb chromatin domains can erode, rendering target genes susceptible to inappropriate gene expression signals. This suggests that activity-based communication and histone modification-dependent thresholds create a localized form of epigenetic memory required for normal PcG chromatin domain function in gene regulation. DOI: http://dx.doi.org/10.7554/eLife.18591.001

Most human aneuploidies originate maternally, due in part to the presence of highly stringent checkpoints during male meiosis. Indeed, male sterility is common among aneuploid mice used to study chromosomal abnormalities, and male germline transmission of exogenous DNA has been rarely reported. Here we show that, despite aberrant testis architecture, males of the aneuploid Tc1 mouse strain produce viable sperm and transmit human chromosome 21 to create aneuploid offspring. In these offspring, we mapped transcription, transcriptional initiation, enhancer activity, non-methylated DNA, and transcription factor binding in adult tissues. Remarkably, when compared with mice derived from female passage of human chromosome 21, the chromatin condensation during spermatogenesis and the extensive epigenetic reprogramming specific to male germline transmission resulted in almost indistinguishable patterns of transcriptional deployment. Our results reveal an unexpected tolerance of aneuploidy during mammalian spermatogenesis, and the surprisingly robust ability of mouse developmental machinery to accurately deploy an exogenous chromosome, regardless of germline transmission. DOI: http://dx.doi.org/10.7554/eLife.20235.001

Mutations of MECP2 ( Methyl-CpG Binding Protein 2 ) cause Rett syndrome. As a chromatin-associated multifunctional protein, how MeCP2 integrates external signals and regulates neuronal function remain unclear. Although neuronal activity-induced phosphorylation of MeCP2 at serine 421 (S421) has been reported, the full spectrum of MeCP2 phosphorylation together with the in vivo function of such modifications are yet to be revealed. Here, we report the identification of several MeCP2 phosphorylation sites in normal and epileptic brains from multiple species. We demonstrate that serine 80 (S80) phosphorylation of MeCP2 is critical as its mutation into alanine (S80A) in transgenic knock-in mice leads to locomotor deficits. S80A mutation attenuates MeCP2 chromatin association at several gene promoters in resting neurons and leads to transcription changes of a small number of genes. Calcium influx in neurons causes dephosphorylation at S80, potentially contributing to its dissociation from the chromatin. We postulate that phosphorylation of MeCP2 modulates its dynamic function in neurons transiting between resting and active states within neural circuits that underlie behaviors.

Mutations of human PHF8 cluster within its JmjC encoding exons and are linked to mental retardation (MR) and a cleft lip/palate phenotype. Sequence comparisons, employing structural insights, suggest that PHF8 contains the double stranded beta-helix fold and ferrous iron binding residues that are present in 2-oxoglutarate-dependent oxygenases. We report that recombinant PHF8 is an Fe(II) and 2-oxoglutarate-dependent N(epsilon)-methyl lysine demethylase, which acts on histone substrates. PHF8 is selective in vitro for N(epsilon)-di- and mono-methylated lysine residues and does not accept trimethyl substrates. Clinically observed mutations to the PHF8 gene cluster in exons encoding for the double stranded beta-helix fold and will therefore disrupt catalytic activity. The PHF8 missense mutation c.836C>T is associated with mild MR, mild dysmorphic features, and either unilateral or bilateral cleft lip and cleft palate in two male siblings. This mutant encodes a F279S variant of PHF8 that modifies a conserved hydrophobic region; assays with both peptides and intact histones reveal this variant to be catalytically inactive. The dependence of PHF8 activity on oxygen availability is interesting because the occurrence of fetal cleft lip has been demonstrated to increase with maternal hypoxia in mouse studies. Cleft lip and other congenital anomalies are also linked indirectly to maternal hypoxia in humans, including from maternal smoking and maternal anti-hypertensive treatment. Our results will enable further studies aimed at defining the molecular links between developmental changes in histone methylation status, congenital disorders and MR.

Methylation of DNA at position five of the cytosine ring occurs at most CpG dinucleotides in the mammalian genome and is essential for embryonic viability. With several of the key proteins now known, it has become possible to approach the biological significance of this epigenetic system through both biochemistry and genetics. As a result, advances have been made in our understanding of the mechanisms by which DNA methylation is targeted to specific regions of the genome and interpreted by methyl-CpG-binding proteins. Recent studies have illuminated the role of DNA methylation in controlling gene expression and have strengthened its links with histone modification and chromatin remodelling.

Histone methylation has important roles in regulating gene expression and forms part of the epigenetic memory system that regulates cell fate and identity. Enzymes that directly remove methyl marks from histones have recently been identified, revealing a new level of plasticity within this epigenetic modification system. Here we analyse the evolutionary relationship between Jumonji C (JmjC)-domain-containing proteins and discuss their cellular functions in relation to their potential enzymatic activities.

Post-translational modification of chromatin has profound effects on many biological processes including transcriptional regulation, heterochromatin organization, and X-chromosome inactivation. Recent studies indicate that methylation on specific histone lysine (K) residues participates in many of these processes. Lysine methylation occurs in three distinct states, having either one (me1), two (me2) or three (me3) methyl groups attached to the amine group of the lysine side chain. These differences in modification state have an important role in defining how methylated chromatin is recognized and interpreted. Until recently, histone lysine methylation was considered a stable modification, but the identification of histone demethylase enzymes has demonstrated the reversibility of this epigenetic mark. So far, all characterized histone demethylases show enzymatic activity towards lysine residues modified in the me1 or me2 state, leaving open the possibility that me3 constitutes an irreversible modification. Here we demonstrate that JHDM3A (jumonji C (JmjC)-domain-containing histone demethylase 3A; also known as JMJD2A) is capable of removing the me3 group from modified H3 lysine 9 (H3K9) and H3 lysine 36 (H3K36). Overexpression of JHDM3A abrogates recruitment of HP1 (heterochromatin protein 1) to heterochromatin, indicating a role for JHDM3A in antagonizing methylated H3K9 nucleated events. siRNA-mediated knockdown of JHDM3A leads to increased levels of H3K9 methylation and upregulation of a JHDM3A target gene, ASCL2, indicating that JHDM3A may function in euchromatin to remove histone methylation marks that are associated with active transcription.

Post-translational modification of chromatin is emerging as an increasingly important regulator of chromosomal processes. In particular, histone lysine and arginine methylation play important roles in regulating transcription, maintaining genomic integrity, and contributing to epigenetic memory. Recently, the use of new approaches to analyse histone methylation, the generation of genetic model systems, and the ability to interrogate genome wide histone modification profiles has aided in defining how histone methylation contributes to these processes. Here we focus on the recent advances in our understanding of the histone methylation system and examine how dynamic histone methylation contributes to normal cellular function in mammals.

Vertebrate DNA can be chemically modified by methylation of the 5 position of the cytosine base in the context of CpG dinucleotides. This modification creates a binding site for MBD (methyl-CpG-binding domain) proteins which target chromatin-modifying activities that are thought to contribute to transcriptional repression and maintain heterochromatic regions of the genome. In contrast with DNA methylation, which is found broadly across vertebrate genomes, non-methylated DNA is concentrated in regions known as CGIs (CpG islands). Recently, a family of proteins which encode a ZF-CxxC (zinc finger-CxxC) domain have been shown to specifically recognize non-methylated DNA and recruit chromatin-modifying activities to CGI elements. For example, CFP1 (CxxC finger protein 1), MLL (mixed lineage leukaemia protein), KDM (lysine demethylase) 2A and KDM2B regulate lysine methylation on histone tails, whereas TET (ten-eleven translocation) 1 and TET3 hydroxylate methylated cytosine bases. In the present review, we discuss the most recent advances in our understanding of how ZF-CxxC domain-containing proteins recognize non-methylated DNA and describe their role in chromatin modification at CGIs. © 2013 The Author(s).

The JmjC oxygenases catalyze the N-demethylation of N(ε)-methyl lysine residues in histones and are current therapeutic targets. A set of human 2-oxoglutarate analogues were screened using a unified assay platform for JmjC demethylases and related oxygenases. Results led to the finding that daminozide (N-(dimethylamino)succinamic acid, 160 Da), a plant growth regulator, selectively inhibits the KDM2/7 JmjC subfamily. Kinetic and crystallographic studies reveal that daminozide chelates the active site metal via its hydrazide carbonyl and dimethylamino groups.

Summary In higher eukaryotes, up to 70% of genes have high levels of nonmethylated cytosine/guanine base pairs (CpGs) surrounding promoters and gene regulatory units. These features, called CpG islands, were identified over 20 years ago, but there remains little mechanistic evidence to suggest how these enigmatic elements contribute to promoter function, except that they are refractory to epigenetic silencing by DNA methylation. Here we show that CpG islands directly recruit the H3K36-specific lysine demethylase enzyme KDM2A. Nucleation of KDM2A at these elements results in removal of H3K36 methylation, creating CpG island chromatin that is uniquely depleted of this modification. KDM2A utilizes a zinc finger CxxC (ZF-CxxC) domain that preferentially recognizes nonmethylated CpG DNA, and binding is blocked when the CpG DNA is methylated, thus constraining KDM2A to nonmethylated CpG islands. These data expose a straightforward mechanism through which KDM2A delineates a unique architecture that differentiates CpG island chromatin from bulk chromatin., Highlights ► A ZF-CxxC domain in KDM2A specifically binds nonmethylated CpG dinucleotides ► KDM2A is targeted to nonmethylated CpG islands genome-wide ► KDM2A actively removes histone H3 lysine 36 dimethylation from CpG islands ► This unique chromatin architecture distinguishes CpG islands from bulk chromatin