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The commonly mutated genes in pancreatic neuroendocrine tumors (PanNETs) are ATRX, DAXX, and MEN1. We genotyped 64 PanNETs and found 58% carry ATRX, DAXX, and MEN1 mutations (A-D-M mutant PanNETs) and this correlates with a worse clinical outcome than tumors carrying the wild-type alleles of all three genes (A-D-M WT PanNETs). We performed RNA sequencing and DNA-methylation analysis to reveal two distinct subgroups with one consisting entirely of A-D-M mutant PanNETs. Two genes differentiating A-D-M mutant from A-D-M WT PanNETs were high ARX and low PDX1 gene expression with PDX1 promoter hyper-methylation in the A-D-M mutant PanNETs. Moreover, A-D-M mutant PanNETs had a gene expression signature related to that of alpha-cells (FDR q-value < 0.009) of pancreatic islets including increased expression of HNF1A and its transcriptional target genes. This gene expression profile suggests that A-D-M mutant PanNETs originate from or transdifferentiate into a distinct cell type similar to alpha cells.

Peripheral nerve lesions provoke apoptosis in the dorsal horn of the spinal cord. The cause of cell death, the involvement of neurons, and the relevance for the processing of somatosensory information are controversial. Here, we demonstrate in a mouse model of sciatic nerve injury that glutamate-induced neurodegeneration and loss of γ-aminobutyric acid (GABA)ergic interneurons in the superficial dorsal horn promote the transition from acute to chronic neuropathic pain. Conditional deletion of Grin1, the essential subunit of N-methyl-d-aspartate-type glutamate receptors (NMDARs), protects dorsal horn neurons from excitotoxicity and preserves GABAergic inhibition. Mice deficient in functional NMDARs exhibit normal nociceptive responses and acute pain after nerve injury, but this initial increase in pain sensitivity is reversible. Eliminating NMDARs fully prevents persistent pain-like behavior. Reduced pain in mice lacking proapoptotic Bax confirmed the significance of neurodegeneration. We conclude that NMDAR-mediated neuron death contributes to the development of chronic neuropathic pain., (Copyright © 2018 The Authors. Published by Elsevier Inc. All rights reserved.)

A robust network of transcription factors and an open chromatin landscape are hallmarks of the naive pluripotent state. Recently, the acetyllysine reader Brd4 has been implicated in stem cell maintenance, but the relative contribution of Brd4 to pluripotency remains unclear. Here, we show that Brd4 is dispensable for self-renewal and pluripotency of embryonic stem cells (ESCs). When maintained in their ground state, ESCs retain transcription factor binding and chromatin accessibility independent of Brd4 function or expression. In metastable ESCs, Brd4 independence can be achieved by increased expression of pluripotency transcription factors, including STAT3, Nanog or Klf4, so long as the DNA methylcytosine oxidases Tet1 and Tet2 are present. These data reveal that Brd4 is not essential for ESC self-renewal. Rather, the levels of pluripotency transcription factor abundance and Tet1/2 function determine the extent to which bromodomain recognition of protein acetylation contributes to the maintenance of gene expression and cell identity.

Derepression of chromatin-mediated transcriptional repression of paternal and maternal genomes is considered the first major step that initiates zygotic gene expression after fertilization. The histone variant H3.3 is present in both male and female gametes and is thought to be important for remodeling the paternal and maternal genomes for activation during both fertilization and embryogenesis. However, the underlying mechanisms remain poorly understood. Using our H3.3B-HA-tagged mouse model, engineered to report H3.3 expression in live animals and to distinguish different sources of H3.3 protein in embryos, we show here that sperm-derived H3.3 (sH3.3) protein is removed from the sperm genome shortly after fertilization and extruded from the zygotes via the second polar bodies (PBII) during embryogenesis. We also found that the maternal H3.3 (mH3.3) protein is incorporated into the paternal genome as early as 2 h postfertilization and is detectable in the paternal genome until the morula stage. Knockdown of maternal H3.3 resulted in compromised embryonic development both of fertilized embryos and of androgenetic haploid embryos. Furthermore, we report that mH3.3 depletion in oocytes impairs both activation of the Oct4 pluripotency marker gene and global de novo transcription from the paternal genome important for early embryonic development. Our results suggest that H3.3-mediated paternal chromatin remodeling is essential for the development of preimplantation embryos and the activation of the paternal genome during embryogenesis., (© 2018 by The American Society for Biochemistry and Molecular Biology, Inc.)

N-α-acetyltransferase D (NatD) mediates N-α-terminal acetylation (Nt-acetylation) of histone H4 known to be involved in cell growth. Here we report that NatD promotes the migratory and invasive capabilities of lung cancer cells in vitro and in vivo. Depletion of NatD suppresses the epithelial-to-mesenchymal transition (EMT) of lung cancer cells by directly repressing the expression of transcription factor Slug, a key regulator of EMT. We found that Nt-acetylation of histone H4 antagonizes histone H4 serine 1 phosphorylation (H4S1ph), and that downregulation of Nt-acetylation of histone H4 facilitates CK2α binding to histone H4 in lung cancer cells, resulting in increased H4S1ph and epigenetic reprogramming to suppress Slug transcription to inhibit EMT. Importantly, NatD is commonly upregulated in primary human lung cancer tissues where its expression level correlates with Slug expression, enhanced invasiveness, and poor clinical outcomes. These findings indicate that NatD is a crucial epigenetic modulator of cell invasion during lung cancer progression.NatD is an acetyltransferase responsible for N-α-terminal acetylation of the histone H4 and H2A and has been linked to cell growth. Here the authors show that NatD-mediated acetylation of histone H4 serine 1 competes with the phosphorylation by CK2α at the same residue thus leading to the upregulation of Slug and tumor progression.

Fragile X syndrome (FXS) is a leading genetic cause of intellectual disability and autism. FXS results from the loss of function of fragile X mental retardation protein (FMRP), which represses translation of target transcripts. Most of the well-characterized target transcripts of FMRP are synaptic proteins, yet targeting these proteins has not provided effective treatments. We examined a group of FMRP targets that encode transcriptional regulators, particularly chromatin-associated proteins. Loss of FMRP in mice results in widespread changes in chromatin regulation and aberrant gene expression. To determine if targeting epigenetic factors could reverse phenotypes associated with the disorder, we focused on Brd4, a BET protein and chromatin reader targeted by FMRP. Inhibition of Brd4 function alleviated many of the phenotypes associated with FXS. We conclude that loss of FMRP results in significant epigenetic misregulation and that targeting transcription via epigenetic regulators like Brd4 may provide new treatments for FXS., (Copyright © 2017 Elsevier Inc. All rights reserved.)

ATP-dependent chromatin remodellers regulate access to genetic information by controlling nucleosome positions in vivo. However, the mechanism by which remodellers discriminate between different nucleosome substrates is poorly understood. Many chromatin remodelling proteins possess conserved protein domains that interact with nucleosomal features. Here we used a quantitative high-throughput approach, based on the use of a DNA-barcoded mononucleosome library, to profile the biochemical activity of human ISWI family remodellers in response to a diverse set of nucleosome modifications. We show that accessory (non-ATPase) subunits of ISWI remodellers can distinguish between differentially modified nucleosomes, directing remodelling activity towards specific nucleosome substrates according to their modification state. Unexpectedly, we show that the nucleosome acidic patch is necessary for maximum activity of all ISWI remodellers evaluated. This dependence also extends to CHD and SWI/SNF family remodellers, suggesting that the acidic patch may be generally required for chromatin remodelling. Critically, remodelling activity can be regulated by modifications neighbouring the acidic patch, signifying that it may act as a tunable interaction hotspot for ATP-dependent chromatin remodellers and, by extension, many other chromatin effectors that engage this region of the nucleosome surface.

Background: Mast cells are key effector cells in allergic reactions. When activated to degranulate, they release a plethora of bioactive compounds from their secretory granules, including mast cell-restricted proteases such as tryptase. In a previous study, we showed that tryptase, in addition to its intragranular location, can be found within the nuclei of mast cells where it truncates core histones at their N-terminal ends., Objective: Considering that the N-terminal portions of the core histones constitute sites for posttranslational modifications of major epigenetic impact, we evaluated whether histone truncation by tryptase could have an impact on epigenetic events in mast cells., Methods: Mast cells were cultured from wild-type and tryptase null mice, followed by an assessment of their profile of epigenetic histone modifications and their phenotypic characteristics., Results: We show that tryptase truncates nucleosomal histone 3 and histone 2B (H2B) and that its absence results in accumulation of the epigenetic mark, lysine 5-acetylated H2B. Intriguingly, the accumulation of lysine 5-acetylated H2B was cell age-dependent and was associated with a profound upregulation of markers of non-mast cell lineages, loss of proliferative control, chromatin remodeling as well as extensive morphological alterations., Conclusions: These findings introduce tryptase-catalyzed histone clipping as a novel epigenetic regulatory mechanism, which in the mast cell context may be crucial for maintaining cellular identity., (Copyright © 2017 The Authors. Published by Elsevier Inc. All rights reserved.)

Competing Interests: The author declares no conflict of interest.

Cancer cells are characterized by aberrant epigenetic landscapes and often exploit chromatin machinery to activate oncogenic gene expression programs. Recognition of modified histones by 'reader' proteins constitutes a key mechanism underlying these processes; therefore, targeting such pathways holds clinical promise, as exemplified by the development of bromodomain and extra-terminal (BET) inhibitors. We recently identified the YEATS domain as an acetyl-lysine-binding module, but its functional importance in human cancer remains unknown. Here we show that the YEATS domain-containing protein ENL, but not its paralogue AF9, is required for disease maintenance in acute myeloid leukaemia. CRISPR-Cas9-mediated depletion of ENL led to anti-leukaemic effects, including increased terminal myeloid differentiation and suppression of leukaemia growth in vitro and in vivo. Biochemical and crystal structural studies and chromatin-immunoprecipitation followed by sequencing analyses revealed that ENL binds to acetylated histone H3, and co-localizes with H3K27ac and H3K9ac on the promoters of actively transcribed genes that are essential for leukaemia. Disrupting the interaction between the YEATS domain and histone acetylation via structure-based mutagenesis reduced the recruitment of RNA polymerase II to ENL-target genes, leading to the suppression of oncogenic gene expression programs. Notably, disrupting the functionality of ENL further sensitized leukaemia cells to BET inhibitors. Together, our data identify ENL as a histone acetylation reader that regulates oncogenic transcriptional programs in acute myeloid leukaemia, and suggest that displacement of ENL from chromatin may be a promising epigenetic therapy, alone or in combination with BET inhibitors, for aggressive leukaemia.

Human papillomavirus (HPV)-negative head and neck squamous cell carcinomas (HNSCCs) are deadly and common cancers. Recent genomic studies implicate multiple genetic pathways, including cell signaling, cell cycle and immune evasion, in their development. Here we analyze public data sets and uncover a previously unappreciated role of epigenome deregulation in the genesis of 13% of HPV-negative HNSCCs. Specifically, we identify novel recurrent mutations encoding p.Lys36Met (K36M) alterations in multiple H3 histone genes. histones. We further validate the presence of these alterations in multiple independent HNSCC data sets and show that, along with previously described NSD1 mutations, they correspond to a specific DNA methylation cluster. The K36M substitution and NSD1 defects converge on altering methylation of histone H3 at K36 (H3K36), subsequently blocking cellular differentiation and promoting oncogenesis. Our data further indicate limited redundancy for NSD family members in HPV-negative HNSCCs and suggest a potential role for impaired H3K36 methylation in their development. Further investigation of drugs targeting chromatin regulators is warranted in HPV-negative HNSCCs driven by aberrant H3K36 methylation.

Eight types of short-chain Lys acylations have recently been identified on histones: propionylation, butyrylation, 2-hydroxyisobutyrylation, succinylation, malonylation, glutarylation, crotonylation and β-hydroxybutyrylation. Emerging evidence suggests that these histone modifications affect gene expression and are structurally and functionally different from the widely studied histone Lys acetylation. In this Review, we discuss the regulation of non-acetyl histone acylation by enzymatic and metabolic mechanisms, the acylation 'reader' proteins that mediate the effects of different acylations and their physiological functions, which include signal-dependent gene activation, spermatogenesis, tissue injury and metabolic stress. We propose a model to explain our present understanding of how differential histone acylation is regulated by the metabolism of the different acyl-CoA forms, which in turn modulates the regulation of gene expression.

Four studies in this issue report new mechanisms underlying the function of the chromatin remodeling SWI/SNF complex in controlling gene expression and suppressing tumor development, providing valuable insights into the treatment of cancers harboring mutations in genes encoding SWI/SNF complex subunits.

Recurrent missense mutations in histone H3 were recently reported in pediatric gliomas and soft tissue tumors. Strikingly, these mutations only affected a minority of the total cellular H3 proteins and occurred at or near lysine residues at positions 27 and 36 on the amino-terminal tail of H3 that are subject to well-characterized posttranslational modifications. Here we review recent progress in elucidating the mechanisms by which these mutations perturb the chromatin landscape in cells through their effects on chromatin-modifying machinery, particularly through inhibition of specific histone lysine methyltransferases. One common feature of histone mutations is their ability to arrest cells in a primitive state refractory to differentiation induction, highlighting the importance of studying these mutations in their proper developmental context., (Copyright © 2017 Cold Spring Harbor Laboratory Press; all rights reserved.)

Recognition of histone covalent modifications by 'reader' modules constitutes a major mechanism for epigenetic regulation. A recent upsurge of newly discovered histone lysine acylations, such as crotonylation (Kcr), butyrylation (Kbu), and propionylation (Kpr), greatly expands the coding potential of histone lysine modifications. Here we demonstrate that the histone acetylation-binding double PHD finger (DPF) domains of human MOZ (also known as KAT6A) and DPF2 (also known as BAF45d) accommodate a wide range of histone lysine acylations with the strongest preference for Kcr. Crystal structures of the DPF domain of MOZ in complex with H3K14cr, H3K14bu, and H3K14pr peptides reveal that these non-acetyl acylations are anchored in a hydrophobic 'dead-end' pocket with selectivity for crotonylation arising from intimate encapsulation and an amide-sensing hydrogen bonding network. Immunofluorescence and chromatin immunoprecipitation (ChIP)-quantitative PCR (qPCR) showed that MOZ and H3K14cr colocalize in a DPF-dependent manner. Our studies call attention to a new regulatory mechanism centered on histone crotonylation readout by DPF family members., Competing Interests: The authors declare no competing financial interest.

Human major depressive disorder (MDD), along with related mood disorders, is among the world's greatest public health concerns; however, its pathophysiology remains poorly understood. Persistent changes in gene expression are known to promote physiological aberrations implicated in MDD. More recently, histone mechanisms affecting cell type- and regional-specific chromatin structures have also been shown to contribute to transcriptional programs related to depressive behaviors, as well as responses to antidepressants. Although much emphasis has been placed in recent years on roles for histone posttranslational modifications and chromatin-remodeling events in the etiology of MDD, it has become increasingly clear that replication-independent histone variants (e.g., H3.3), which differ in primary amino acid sequence from their canonical counterparts, similarly play critical roles in the regulation of activity-dependent neuronal transcription, synaptic connectivity, and behavioral plasticity. Here, we demonstrate a role for increased H3.3 dynamics in the nucleus accumbens (NAc)-a key limbic brain reward region-in the regulation of aberrant social stress-mediated gene expression and the precipitation of depressive-like behaviors in mice. We find that molecular blockade of these dynamics promotes resilience to chronic social stress and results in a partial renormalization of stress-associated transcriptional patterns in the NAc. In sum, our findings establish H3.3 dynamics as a critical, and previously undocumented, regulator of mood and suggest that future therapies aimed at modulating striatal histone dynamics may potentiate beneficial behavioral adaptations to negative emotional stimuli., Competing Interests: The authors declare no conflict of interest.

The inflammatory response requires coordinated activation of both transcription factors and chromatin to induce transcription for defense against pathogens and environmental insults. We sought to elucidate the connections between inflammatory signaling pathways and chromatin through genomic footprinting of kinase activity and unbiased identification of prominent histone phosphorylation events. We identified H3 serine 28 phosphorylation (H3S28ph) as the principal stimulation-dependent histone modification and observed its enrichment at induced genes in mouse macrophages stimulated with bacterial lipopolysaccharide. Using pharmacological and genetic approaches, we identified mitogen- and stress-activated protein kinases (MSKs) as primary mediators of H3S28ph in macrophages. Cell-free transcription assays demonstrated that H3S28ph directly promotes p300/CBP-dependent transcription. Further, MSKs can activate both signal-responsive transcription factors and the chromatin template with additive effects on transcription. Specific inhibition of MSKs in macrophages selectively reduced transcription of stimulation-induced genes. Our results suggest that MSKs incorporate upstream signaling inputs and control multiple downstream regulators of inducible transcription., (Copyright © 2016 Elsevier Inc. All rights reserved.)

Repeated cocaine exposure regulates transcriptional regulation within the nucleus accumbens (NAc), and epigenetic mechanisms-such as histone acetylation and methylation on Lys residues-have been linked to these lasting actions of cocaine. In contrast to Lys methylation, the role of histone Arg (R) methylation remains underexplored in addiction models. Here we show that protein-R-methyltransferase-6 (PRMT6) and its associated histone mark, asymmetric dimethylation of R2 on histone H3 (H3R2me2a), are decreased in the NAc of mice and rats after repeated cocaine exposure, including self-administration, and in the NAc of cocaine-addicted humans. Such PRMT6 down-regulation occurs selectively in NAc medium spiny neurons (MSNs) expressing dopamine D2 receptors (D2-MSNs), with opposite regulation occurring in D1-MSNs, and serves to protect against cocaine-induced addictive-like behavioral abnormalities. Using ChIP-seq, we identified Src kinase signaling inhibitor 1 (Srcin1; also referred to as p140Cap) as a key gene target for reduced H3R2me2a binding, and found that consequent Srcin1 induction in the NAc decreases Src signaling, cocaine reward, and the motivation to self-administer cocaine. Taken together, these findings suggest that suppression of Src signaling in NAc D2-MSNs, via PRMT6 and H3R2me2a down-regulation, functions as a homeostatic brake to restrain cocaine action, and provide novel candidates for the development of treatments for cocaine addiction., Competing Interests: The authors declare no conflict of interest.

Over the past 20 years, breakthrough discoveries of chromatin-modifying enzymes and associated mechanisms that alter chromatin in response to physiological or pathological signals have transformed our knowledge of epigenetics from a collection of curious biological phenomena to a functionally dissected research field. Here, we provide a personal perspective on the development of epigenetics, from its historical origins to what we define as 'the modern era of epigenetic research'. We primarily highlight key molecular mechanisms of and conceptual advances in epigenetic control that have changed our understanding of normal and perturbed development.

High-frequency point mutations of genes encoding histones have been identified recently as novel drivers in a number of tumors. Specifically, the H3K36M/I mutations were shown to be oncogenic in chondroblastomas and undifferentiated sarcomas by inhibiting H3K36 methyltransferases, including SETD2. Here we report the crystal structures of the SETD2 catalytic domain bound to H3K36M or H3K36I peptides with SAH (S-adenosylhomocysteine). In the complex structure, the catalytic domain adopts an open conformation, with the K36M/I peptide snuggly positioned in a newly formed substrate channel. Our structural and biochemical data reveal the molecular basis underying oncohistone recognition by and inhibition of SETD2., (© 2016 Yang et al.; Published by Cold Spring Harbor Laboratory Press.)

Chordoma is a rare primary bone neoplasm that is resistant to standard chemotherapies. Despite aggressive surgical management, local recurrence and metastasis is not uncommon. To identify the specific genetic aberrations that play key roles in chordoma pathogenesis, we utilized a genome-wide high-resolution SNP-array and next generation sequencing (NGS)-based molecular profiling platform to study 24 patient samples with typical histopathologic features of chordoma. Matching normal tissues were available for 16 samples. SNP-array analysis revealed nonrandom copy number losses across the genome, frequently involving 3, 9p, 1p, 14, 10, and 13. In contrast, copy number gain is uncommon in chordomas. Two minimum deleted regions were observed on 3p within a ∼8 Mb segment at 3p21.1-p21.31, which overlaps SETD2, BAP1 and PBRM1. The minimum deleted region on 9p was mapped to CDKN2A locus at 9p21.3, and homozygous deletion of CDKN2A was detected in 5/22 chordomas (∼23%). NGS-based molecular profiling demonstrated an extremely low level of mutation rate in chordomas, with an average of 0.5 mutations per sample for the 16 cases with matched normal. When the mutated genes were grouped based on molecular functions, many of the mutation events (∼40%) were found in chromatin regulatory genes. The combined copy number and mutation profiling revealed that SETD2 is the single gene affected most frequently in chordomas, either by deletion or by mutations. Our study demonstrated that chordoma belongs to the C-class (copy number changes) tumors whose oncogenic signature is non-random multiple copy number losses across the genome and genomic aberrations frequently alter chromatin regulatory genes. © 2016 Wiley Periodicals, Inc., (© 2016 Wiley Periodicals, Inc.)

Information encoded in DNA is interpreted, modified, and propagated as chromatin. The diversity of inputs encountered by eukaryotic genomes demands a matching capacity for transcriptional outcomes provided by the combinatorial and dynamic nature of epigenetic processes. Advances in genome editing, visualization technology, and genome-wide analyses have revealed unprecedented complexity of chromatin pathways, offering explanations to long-standing questions and presenting new challenges. Here, we review recent findings, exemplified by the emerging understanding of crossregulatory interactions within chromatin, and emphasize the pathologic outcomes of epigenetic misregulation in cancer., (Copyright © 2016 Elsevier Inc. All rights reserved.)

Lysine to methionine (K-to-M) mutations in genes encoding histone H3 are thought to drive a subset of pediatric brain and bone cancers. These high-frequency K-to-M mutations occur at sites of methylation on histone H3, and tumors containing the mutant histones exhibit a global loss of specific histone methylation marks. Previous studies showed that K-to-M mutant histones, also known as oncohistones, are potent orthosteric inhibitors of specific Su(var)3-9, Enhancer-of-zeste, Trithorax (SET) domain methyltransferases. However, the biochemical and biophysical details of the interaction between K-to-M mutant histones and the respective SET domain methyltransferases are currently unknown. Here, we use the histone H3K9-directed methyltransferase G9a as a model to explore the mechanism of inhibition by K-to-M oncohistones. X-ray cocrystal structures revealed that the K9M residue of histone H3 occupies the active site cavity of G9a, and kinetic analysis indicates competitive inhibition of G9a by histone H3K9M. Additionally, we find that the cofactor S-adenosyl methionine (SAM) is necessary for stable interaction between G9a and H3K9M histone. Consistent with the formation of a ternary complex, we find that the inhibitory peptide is uncompetitive with regard to SAM. These data and others indicate that K-to-M oncohistones promote global loss of specific lysine methylation through sequestration and inhibition of SAM-bound SET domain methyltransferases.

Several types of pediatric cancers reportedly contain high-frequency missense mutations in histone H3, yet the underlying oncogenic mechanism remains poorly characterized. Here we report that the H3 lysine 36-to-methionine (H3K36M) mutation impairs the differentiation of mesenchymal progenitor cells and generates undifferentiated sarcoma in vivo. H3K36M mutant nucleosomes inhibit the enzymatic activities of several H3K36 methyltransferases. Depleting H3K36 methyltransferases, or expressing an H3K36I mutant that similarly inhibits H3K36 methylation, is sufficient to phenocopy the H3K36M mutation. After the loss of H3K36 methylation, a genome-wide gain in H3K27 methylation leads to a redistribution of polycomb repressive complex 1 and de-repression of its target genes known to block mesenchymal differentiation. Our findings are mirrored in human undifferentiated sarcomas in which novel K36M/I mutations in H3.1 are identified., (Copyright © 2016, American Association for the Advancement of Science.)

Spermatogonial stem and progenitor cells (SSCs) generate adult male gametes. During in vitro expansion, these unipotent murine cells spontaneously convert to multipotent adult spermatogonial-derived stem cells (MASCs). Here we investigate this conversion process through integrative transcriptomic and epigenomic analyses. We find in SSCs that promoters essential to maintenance and differentiation of embryonic stem cells (ESCs) are enriched with histone H3-lysine4 and -lysine 27 trimethylations. These bivalent modifications are maintained at most somatic promoters after conversion, bestowing MASCs an ESC-like promoter chromatin. At enhancers, the core pluripotency circuitry is activated partially in SSCs and completely in MASCs, concomitant with loss of germ cell-specific gene expression and initiation of embryonic-like programs. Furthermore, SSCs in vitro maintain the epigenomic characteristics of germ cells in vivo. Our observations suggest that SSCs encode innate plasticity through the epigenome and that both conversion of promoter chromatin states and activation of cell type-specific enhancers are prominent features of reprogramming.

Recognition of histone covalent modifications by chromatin-binding protein modules ("readers") constitutes a major mechanism for epigenetic regulation, typified by bromodomains that bind acetyllysine. Non-acetyl histone lysine acylations (e.g., crotonylation, butyrylation, propionylation) have been recently identified, but readers that prefer these acylations have not been characterized. Here we report that the AF9 YEATS domain displays selectively higher binding affinity for crotonyllysine over acetyllysine. Structural studies revealed an extended aromatic sandwiching cage with crotonyl specificity arising from π-aromatic and hydrophobic interactions between crotonyl and aromatic rings. These features are conserved among the YEATS, but not the bromodomains. Using a cell-based model, we showed that AF9 co-localizes with crotonylated histone H3 and positively regulates gene expression in a YEATS domain-dependent manner. Our studies define the evolutionarily conserved YEATS domain as a family of crotonyllysine readers and specifically demonstrate that the YEATS domain of AF9 directly links histone crotonylation to active transcription., (Copyright © 2016 Elsevier Inc. All rights reserved.)

Covalent modifications of both DNA and histones act in concert to define the landscape of our epigenome. In this review, we explore the interconnections between histone and DNA modifications by focusing on a conserved chromatin-binding regulatory domain, the ATRX-DNMT3-DNMT3L (ADD) domain. New studies show that the ADD domain is capable of sensing, and therefore integrating, the status of multiple histone modifications. This in turn dictates the in vivo localization or allosteric regulation of the full-length ADD-containing protein and its ability to function in downstream chromatin remodeling events. Strategies to re-engineer the ADD "reader pocket" in the de novo DNA methyltransferase DNMT3A such that it redirects this "writer" to new genomic loci proved useful in understanding important biological downstream consequences of mis-targeting of DNA methylation via altered reading of histone marks. Combined with genome-editing tools, this approach stands as a poof-of-principle and will be broadly applicable to the elucidation of epigenetic networks that have been altered by "reader" mutations, either artificially or as naturally occurs in some human diseases.

Precise regulation of transcription is crucial for the cellular mechanisms underlying memory formation. However, the link between neuronal stimulation and the proteins that directly interact with histone modifications to activate transcription in neurons remains unclear. Brd4 is a member of the bromodomain and extra-terminal domain (BET) protein family, which binds acetylated histones and is a critical regulator of transcription in many cell types, including transcription in response to external cues. Small molecule BET inhibitors are in clinical trials, yet almost nothing is known about Brd4 function in the brain. Here we show that Brd4 mediates the transcriptional regulation underlying learning and memory. The loss of Brd4 function affects critical synaptic proteins, which results in memory deficits in mice but also decreases seizure susceptibility. Thus Brd4 provides a critical link between neuronal activation and the transcriptional responses that occur during memory formation.

Improved treatment for major depressive disorder (MDD) remains elusive because of the limited understanding of its underlying biological mechanisms. It is likely that stress-induced maladaptive transcriptional regulation in limbic neural circuits contributes to the development of MDD, possibly through epigenetic factors that regulate chromatin structure. We establish that persistent upregulation of the ACF (ATP-utilizing chromatin assembly and remodeling factor) ATP-dependent chromatin-remodeling complex, occurring in the nucleus accumbens of stress-susceptible mice and depressed humans, is necessary for stress-induced depressive-like behaviors. We found that altered ACF binding after chronic stress was correlated with altered nucleosome positioning, particularly around the transcription start sites of affected genes. These alterations in ACF binding and nucleosome positioning were associated with repressed expression of genes implicated in susceptibility to stress. Together, our findings identify the ACF chromatin-remodeling complex as a critical component in the development of susceptibility to depression and in regulating stress-related behaviors.

Access to high-quality antibodies is a necessity for the study of histones and their posttranslational modifications (PTMs). Here we debut the Histone Antibody Specificity Database (http://www.histoneantibodies.com), an online and expanding resource cataloging the behavior of widely used, commercially available histone antibodies by peptide microarray. This interactive web portal provides a critical resource to the biological research community that routinely uses these antibodies as detection reagents for a wide range of applications., (Copyright © 2015 Elsevier Inc. All rights reserved.)

Histone modification and DNA methylation are associated with varying epigenetic "landscapes," but detailed mechanistic and functional links between the two remain unclear. Using the ATRX-DNMT3-DNMT3L (ADD) domain of the DNA methyltransferase Dnmt3a as a paradigm, we apply protein engineering to dissect the molecular interactions underlying the recruitment of this enzyme to specific regions of chromatin in mouse embryonic stem cells (ESCs). By rendering the ADD domain insensitive to histone modification, specifically H3K4 methylation or H3T3 phosphorylation, we demonstrate the consequence of dysregulated Dnmt3a binding and activity. Targeting of a Dnmt3a mutant to H3K4me3 promoters decreases gene expression in a subset of developmental genes and alters ESC differentiation, whereas aberrant binding of another mutant to H3T3ph during mitosis promotes chromosome instability. Our studies support the general view that histone modification "reading" and DNA methylation are closely coupled in mammalian cells, and suggest an avenue for the functional assessment of chromatin-associated proteins., (Copyright © 2015 Elsevier Inc. All rights reserved.)

Turnover and exchange of nucleosomal histones and their variants, a process long believed to be static in post-replicative cells, remains largely unexplored in brain. Here, we describe a novel mechanistic role for HIRA (histone cell cycle regulator) and proteasomal degradation-associated histone dynamics in the regulation of activity-dependent transcription, synaptic connectivity, and behavior. We uncover a dramatic developmental profile of nucleosome occupancy across the lifespan of both rodents and humans, with the histone variant H3.3 accumulating to near-saturating levels throughout the neuronal genome by mid-adolescence. Despite such accumulation, H3.3-containing nucleosomes remain highly dynamic-in a modification-independent manner-to control neuronal- and glial-specific gene expression patterns throughout life. Manipulating H3.3 dynamics in both embryonic and adult neurons confirmed its essential role in neuronal plasticity and cognition. Our findings establish histone turnover as a critical and previously undocumented regulator of cell type-specific transcription and plasticity in mammalian brain., (Copyright © 2015 Elsevier Inc. All rights reserved.)

Transposable elements comprise roughly 40% of mammalian genomes. They have an active role in genetic variation, adaptation and evolution through the duplication or deletion of genes or their regulatory elements, and transposable elements themselves can act as alternative promoters for nearby genes, resulting in non-canonical regulation of transcription. However, transposable element activity can lead to detrimental genome instability, and hosts have evolved mechanisms to silence transposable element mobility appropriately. Recent studies have demonstrated that a subset of transposable elements, endogenous retroviral elements (ERVs) containing long terminal repeats (LTRs), are silenced through trimethylation of histone H3 on lysine 9 (H3K9me3) by ESET (also known as SETDB1 or KMT1E) and a co-repressor complex containing KRAB-associated protein 1 (KAP1; also known as TRIM28) in mouse embryonic stem cells. Here we show that the replacement histone variant H3.3 is enriched at class I and class II ERVs, notably those of the early transposon (ETn)/MusD family and intracisternal A-type particles (IAPs). Deposition at a subset of these elements is dependent upon the H3.3 chaperone complex containing α-thalassaemia/mental retardation syndrome X-linked (ATRX) and death-domain-associated protein (DAXX). We demonstrate that recruitment of DAXX, H3.3 and KAP1 to ERVs is co-dependent and occurs upstream of ESET, linking H3.3 to ERV-associated H3K9me3. Importantly, H3K9me3 is reduced at ERVs upon H3.3 deletion, resulting in derepression and dysregulation of adjacent, endogenous genes, along with increased retrotransposition of IAPs. Our study identifies a unique heterochromatin state marked by the presence of both H3.3 and H3K9me3, and establishes an important role for H3.3 in control of ERV retrotransposition in embryonic stem cells.

ATRX (the alpha thalassemia/mental retardation syndrome X-linked protein) is a member of the switch2/sucrose nonfermentable2 (SWI2/SNF2) family of chromatin-remodeling proteins and primarily functions at heterochromatic loci via its recognition of "repressive" histone modifications [e.g., histone H3 lysine 9 tri-methylation (H3K9me3)]. Despite significant roles for ATRX during normal neural development, as well as its relationship to human disease, ATRX function in the central nervous system is not well understood. Here, we describe ATRX's ability to recognize an activity-dependent combinatorial histone modification, histone H3 lysine 9 tri-methylation/serine 10 phosphorylation (H3K9me3S10ph), in postmitotic neurons. In neurons, this "methyl/phos" switch occurs exclusively after periods of stimulation and is highly enriched at heterochromatic repeats associated with centromeres. Using a multifaceted approach, we reveal that H3K9me3S10ph-bound Atrx represses noncoding transcription of centromeric minor satellite sequences during instances of heightened activity. Our results indicate an essential interaction between ATRX and a previously uncharacterized histone modification in the central nervous system and suggest a potential role for abnormal repetitive element transcription in pathological states manifested by ATRX dysfunction.

Acetylation of histones at DNA regulatory elements plays a critical role in transcriptional activation. Histones are also modified by other acyl moieties, including crotonyl, yet the mechanisms that govern acetylation versus crotonylation and the functional consequences of this "choice" remain unclear. We show that the coactivator p300 has both crotonyltransferase and acetyltransferase activities, and that p300-catalyzed histone crotonylation directly stimulates transcription to a greater degree than histone acetylation. Levels of histone crotonylation are regulated by the cellular concentration of crotonyl-CoA, which can be altered through genetic and environmental perturbations. In a cell-based model of transcriptional activation, increasing or decreasing the cellular concentration of crotonyl-CoA leads to enhanced or diminished gene expression, respectively, which correlates with the levels of histone crotonylation flanking the regulatory elements of activated genes. Our findings support a general principle wherein differential histone acylation (i.e., acetylation versus crotonylation) couples cellular metabolism to the regulation of gene expression., (Copyright © 2015 Elsevier Inc. All rights reserved.)

The role of cellular metabolism in regulating cell proliferation and differentiation remains poorly understood. For example, most mammalian cells cannot proliferate without exogenous glutamine supplementation even though glutamine is a non-essential amino acid. Here we show that mouse embryonic stem (ES) cells grown under conditions that maintain naive pluripotency are capable of proliferation in the absence of exogenous glutamine. Despite this, ES cells consume high levels of exogenous glutamine when the metabolite is available. In comparison to more differentiated cells, naive ES cells utilize both glucose and glutamine catabolism to maintain a high level of intracellular α-ketoglutarate (αKG). Consequently, naive ES cells exhibit an elevated αKG to succinate ratio that promotes histone/DNA demethylation and maintains pluripotency. Direct manipulation of the intracellular αKG/succinate ratio is sufficient to regulate multiple chromatin modifications, including H3K27me3 and ten-eleven translocation (Tet)-dependent DNA demethylation, which contribute to the regulation of pluripotency-associated gene expression. In vitro, supplementation with cell-permeable αKG directly supports ES-cell self-renewal while cell-permeable succinate promotes differentiation. This work reveals that intracellular αKG/succinate levels can contribute to the maintenance of cellular identity and have a mechanistic role in the transcriptional and epigenetic state of stem cells.

Over 70% of diffuse intrinsic pediatric gliomas, an aggressive brainstem tumor, harbor heterozygous mutations that create a K27M amino acid substitution (methionine replaces lysine 27) in the tail of histone H3.3. The role of the H3.3K27M mutation in tumorigenesis is not fully understood. Here, we use a human embryonic stem cell system to model this tumor. We show that H3.3K27M expression synergizes with p53 loss and PDGFRA activation in neural progenitor cells derived from human embryonic stem cells, resulting in neoplastic transformation. Genome-wide analyses indicate a resetting of the transformed precursors to a developmentally more primitive stem cell state, with evidence of major modifications of histone marks at several master regulator genes. Drug screening assays identified a compound targeting the protein menin as an inhibitor of tumor cell growth in vitro and in mice., (Copyright © 2014, American Association for the Advancement of Science.)

Chromatin remodeling via incorporation of histone variants plays a key role in the regulation of embryonic development. The histone variant H3.3 has been associated with a number of early events including formation of the paternal pronucleus upon fertilization. The small number of amino acid differences between H3.3 and its canonical counterparts (H3.1 and H3.2) has limited studies of the developmental significance of H3.3 deposition into chromatin due to difficulties in distinguishing the H3 isoforms. To this end, we used zinc-finger nuclease (ZFN) mediated gene editing to introduce a small C-terminal hemagglutinin (HA) tag to the endogenous H3.3B locus in mouse embryonic stem cells (ESCs), along with an internal ribosome entry site (IRES) and a separately translated fluorescent reporter of expression. This system will allow detection of expression driven by the reporter in cells, animals, and embryos, and will facilitate investigation of differential roles of paternal and maternal H3.3 protein during embryogenesis that would not be possible using variant-specific antibodies. Further, the ability to monitor endogenous H3.3 protein in various cell lineages will enhance our understanding of the dynamics of this histone variant over the course of development., (© 2014 Wiley Periodicals, Inc.)

Over the past decade, rapid advances in epigenomics research have extensively characterized critical roles for chromatin regulatory events during normal periods of eukaryotic cell development and plasticity, as well as part of aberrant processes implicated in human disease. Application of such approaches to studies of the CNS, however, is more recent. Here we provide a comprehensive overview of available tools for analyzing neuroepigenomics data, as well as a discussion of pending challenges specific to the field of neuroscience. Integration of numerous unbiased genome-wide and proteomic approaches will be necessary to fully understand the neuroepigenome and the extraordinarily complex nature of the human brain. This will be critical to the development of future diagnostic and therapeutic strategies aimed at alleviating the vast array of heterogeneous and genetically distinct disorders of the CNS.

The histone methyltransferase PRC2 plays a central role in genomic stability and cellular development. Consequently, its misregulation has been implicated in several cancers. Recent work has shown that a histone H3 mutant, where the PRC2 substrate residue Lys27 is replaced by methionine, is also associated with cancer phenotypes and functions as an inhibitor of PRC2. Here we investigate the mechanism of this PRC2 inhibition through kinetic studies and photo-cross-linking. Efficient inhibition is dependent on (1) hydrophobic lysine isosteres blocking the active site, (2) proximal residues, and (3) the H3 tail forming extensive contacts with the EZH2 subunit of PRC2. We further show that naturally occurring post-translational modifications of the same H3 tail, both proximal and distal to K27M, can greatly diminish the inhibition of PRC2. These results suggest that this potent gain of function mutation may be "detoxified" by modulating alternate chromatin modification pathways.