Histone exchange, chromatin structure and the regulation of transcription

Potential epigenetic molecular regulatory networks in ocular neovascularization

Neovascularization is one of the many manifestations of ocular diseases, including corneal injury and vascular diseases of the retina and choroid. Although anti-VEGF drugs have been used to effectively treat neovascularization, long-term use of anti-angiogenic factors can cause a variety of neurological and developmental side effects. As a result, better drugs to treat ocular neovascularization are urgently required. There is mounting evidence that epigenetic regulation is important in ocular neovascularization. DNA methylation and histone modification, non-coding RNA, and mRNA modification are all examples of epigenetic mechanisms. In order to shed new light on epigenetic therapeutics in ocular neovascularization, this review focuses on recent advances in the epigenetic control of ocular neovascularization as well as discusses these new mechanisms.

Aging is associated with increased chromatin accessibility and reduced polymerase pausing in liver

Regulation of gene expression is linked to the organization of the genome. With age, chromatin alterations occur on all levels of genome organization, accompanied by changes in the gene expression profile. However, little is known about the changes in the level of transcriptional regulation. Here, we used a multi‐omics approach and integrated ATAC‐, RNA‐ and NET‐seq to identify age‐related changes in the chromatin landscape of murine liver and to investigate how these are linked to transcriptional regulation. We provide the first systematic inventory of the connection between aging, chromatin accessibility, and transcriptional regulation in a whole tissue. Aging in murine liver is characterized by an increase in chromatin accessibility at promoter regions, but not in an increase in transcriptional output. Instead, aging is accompanied by a decrease in promoter‐proximal pausing of RNA polymerase II (Pol II), while initiation of transcription is not decreased as assessed by RNA polymerase mapping using CUT&RUN. Based on the data reported, we propose that these age‐related changes in transcriptional regulation are due to a reduced stability of the pausing complex.

Identification of N7-methylguanosine-related IncRNA signature as a potential predictive biomarker for colon adenocarcinoma

N⁷-Methylguanosine (m7G) is an RNA modification serving as a key part of colon cancer development. Thus, a comprehensive analysis was executed to explore prognostic roles and associations with the immune status of the m7G-related lncRNA (m7G-RNAs) in colon adenocarcinoma (COAD). Identification of m7G-RNAs was achieved via Pearson’s correlation analysis of lncRNAs in the TCGA-COAD dataset and m7G regulators. A prognostic signature was developed via LASSO analyses. ESTIMATE, CIBERSORT, and ssGSEA algorithms were utilized to assess immune infiltration between different risk groups. Survival analysis suggested the high-risk group possesses poor outcomes compared with the low-risk group. According to the ROC curves, the m7G-RNAs signature exhibited a reliable capability of prediction (AUCs at 1, 3, and 5 years were 0.770, 0.766, and 0.849, respectively). Multivariate hazard analysis proved that the signature was an independent predictive indicator for OS. Moreover, the risk score was related to infiltration levels of naïve B cells, CD4⁺ memory T cells, and resting NK cells. The result revealed the prognostic value of m7G modification in COAD and provided a novel perspective on personalized immunotherapy strategies.

Structural basis of nucleosome disassembly and reassembly by RNAPII elongation complex with FACT

During gene transcription, RNA polymerase II (RNAPII) traverses nucleosomes in chromatin, but its mechanism has remained elusive. Using cryo-electron microscopy, we obtained structures of the RNAPII elongation complex (EC) passing through a nucleosome, in the presence of transcription elongation factors Spt6, Spn1, Elf1, Spt4/5, and Paf1C and the histone chaperone FACT. The structures show snapshots of EC progression on DNA, mediating downstream nucleosome disassembly followed by its reassembly upstream of the EC, facilitated by FACT. FACT dynamically adapts to successively occurring subnucleosome intermediates, forming an interface with the EC. Spt6, Spt4/5, and Paf1C form a "cradle" at the EC DNA-exit site, and support the upstream nucleosome reassembly. These structures explain the mechanism by which the EC traverses nucleosomes while maintaining the chromatin structure and epigenetic information.

Postmitotic accumulation of histone variant H3.3 in new cortical neurons establishes neuronal chromatin, transcriptome, and identity

Histone variants, which can be expressed outside of S-phase and deposited DNA synthesis-independently, provide long-term histone replacement in postmitotic cells, including neurons. Beyond replenishment, histone variants also play active roles in gene regulation by modulating chromatin states or enabling nucleosome turnover. Here, we uncover crucial roles for the histone H3 variant H3.3 in neuronal development. We find that newborn cortical excitatory neurons, which have only just completed replication-coupled deposition of canonical H3.1 and H3.2, substantially accumulate H3.3 immediately postmitosis. Codeletion of H3.3-encoding genes H3f3a and H3f3b from newly postmitotic neurons abrogates H3.3 accumulation, markedly alters the histone posttranslational modification landscape, and causes widespread disruptions to the establishment of the neuronal transcriptome. These changes coincide with developmental phenotypes in neuronal identities and axon projections. Thus, preexisting, replication-dependent histones are insufficient for establishing neuronal chromatin and transcriptome; de novo H3.3 is required. Stage-dependent deletion of H3f3a and H3f3b from 1) cycling neural progenitor cells, 2) neurons immediately postmitosis, or 3) several days later, reveals the first postmitotic days to be a critical window for de novo H3.3. After H3.3 accumulation within this developmental window, codeletion of H3f3a and H3f3b does not lead to immediate H3.3 loss, but causes progressive H3.3 depletion over several months without widespread transcriptional disruptions or cellular phenotypes. Our study thus uncovers key developmental roles for de novo H3.3 in establishing neuronal chromatin, transcriptome, identity, and connectivity immediately postmitosis that are distinct from its role in maintaining total histone H3 levels over the neuronal lifespan.

In Vitro Mapping of Nucleosome Positions at Base-Pair Resolution Using Ortho-Phenanthroline

The positions of nucleosomes along genomic DNA play a role in defining patterns of gene expression and chromatin organization. Determination of nucleosome positions in vivo and in vitro, as revealed by the locations of histones on DNA, has provided insight into mechanisms of nucleosome sliding, spacing, assembly, and disassembly. Here, we describe methods for the in vitro determination of histone-DNA contacts at base-pair (bp) resolution. The protocol involves the labeling of histones with ortho-phenanthroline (OP), site-specific cleavage of nucleosomal DNA, and processing and analysis of the resulting DNA fragments. This methodology provides an efficient and high-resolution means for studying kinetics and behavior of enzymes that alter nucleosome structure and/or positioning, and can be used to identify preferred distributions of nucleosomes on natural DNA sequences. © 2022 Wiley Periodicals LLC. Basic Protocol 1: Cysteine-specific chemical modification of folded histones with ortho-phenanthroline (OP) Basic Protocol 2: Nucleosome sliding assay adapted for OP mapping of histone-DNA contacts Basic Protocol 3: OP-mediated cleavage, processing, and analysis of DNA fragments using a sequencing gel Support Protocol 1: Preparation of dideoxy sequencing ladders Support Protocol 2: Preparation and running of a denaturing DNA sequencing gel.

Chromatin Dynamics in Digestive System Cancer: Commander and Regulator

Digestive system tumors have a poor prognosis due to complex anatomy, insidious onset, challenges in early diagnosis, and chemoresistance. Epidemiological statistics has verified that digestive system tumors rank first in tumor-related death. Although a great number of studies are devoted to the molecular biological mechanism, early diagnostic markers, and application of new targeted drugs in digestive system tumors, the therapeutic effect is still not satisfactory. Epigenomic alterations including histone modification and chromatin remodeling are present in human cancers and are now known to cooperate with genetic changes to drive the cancer phenotype. Chromatin is the carrier of genetic information and consists of DNA, histones, non-histone proteins, and a small amount of RNA. Chromatin and nucleosomes control the stability of the eukaryotic genome and regulate DNA processes such as transcription, replication, and repair. The dynamic structure of chromatin plays a key role in this regulatory function. Structural fluctuations expose internal DNA and thus provide access to the nuclear machinery. The dynamic changes are affected by various complexes and epigenetic modifications. Variation of chromatin dynamics produces early and superior regulation of the expression of related genes and downstream pathways, thereby controlling tumor development. Intervention at the chromatin level can change the process of cancer earlier and is a feasible option for future tumor diagnosis and treatment. In this review, we introduced chromatin dynamics including chromatin remodeling, histone modifications, and chromatin accessibility, and current research on chromatin regulation in digestive system tumors was also summarized.

Tracing the Origin of Cell-Free DNA Molecules through Tissue-Specific Epigenetic Signatures

All cell and tissue types constantly release DNA fragments into human body fluids by various mechanisms including programmed cell death, accidental cell degradation and active extrusion. Particularly, cell-free DNA (cfDNA) in plasma or serum has been utilized for minimally invasive molecular diagnostics. Disease onset or pathological conditions that lead to increased cell death alter the contribution of different tissues to the total pool of cfDNA. Because cfDNA molecules retain cell-type specific epigenetic features, it is possible to infer tissue-of-origin from epigenetic characteristics. Recent research efforts demonstrated that analysis of, e.g., methylation patterns, nucleosome occupancy, and fragmentomics determined the cell- or tissue-of-origin of individual cfDNA molecules. This novel tissue-of origin-analysis enables to estimate the contributions of different tissues to the total cfDNA pool in body fluids and find tissues with increased cell death (pathologic condition), expanding the portfolio of liquid biopsies towards a wide range of pathologies and early diagnosis. In this review, we summarize the currently available tissue-of-origin approaches and point out the next steps towards clinical implementation.

Gene regulation by histone-modifying enzymes under hypoxic conditions: a focus on histone methylation and acetylation

Oxygen, which is necessary for sustaining energy metabolism, is consumed in many biochemical reactions in eukaryotes. When the oxygen supply is insufficient for maintaining multiple homeostatic states at the cellular level, cells are subjected to hypoxic stress. Hypoxia induces adaptive cellular responses mainly through hypoxia-inducible factors (HIFs), which are stabilized and modulate the transcription of various hypoxia-related genes. In addition, many epigenetic regulators, such as DNA methylation, histone modification, histone variants, and adenosine triphosphate-dependent chromatin remodeling factors, play key roles in gene expression. In particular, hypoxic stress influences the activity and gene expression of histone-modifying enzymes, which controls the posttranslational modification of HIFs and histones. This review covers how histone methylation and histone acetylation enzymes modify histone and nonhistone proteins under hypoxic conditions and surveys the impact of epigenetic modifications on gene expression. In addition, future directions in this area are discussed.

New sequencing technologies are revealing how cells respond to hypoxia, insufficient oxygen, by managing gene activation. In multicellular organisms, gene activation is managed by how tightly a section of DNA is wound around proteins called histones; genes in tightly packed regions are inaccessible and inactive, whereas those in looser regions can be activated. Kyunghwan Kim, Sun-Ju Yi, and co-workers at Chungbuk National University in South Korea have reviewed recent data on how cells regulate gene activity under hypoxic conditions. Advances in sequencing technology have allowed genome-wide studies of how hypoxia affects DNA structure and gene activation, revealing that gene-specific modifications may be more important than genome-wide modifications. Hypoxia is implicated in several diseases, such as cancer and chronic metabolic diseases, and a better understanding of how it affects gene activation may help identify new treatments for hypoxia-related diseases.

Sex Differences in Molecular Mechanisms of Cardiovascular Aging

Cardiovascular disease (CVD) is still the leading cause of illness and death in the Western world. Cardiovascular aging is a progressive modification occurring in cardiac and vascular morphology and physiology where increased endothelial dysfunction and arterial stiffness are observed, generally accompanied by increased systolic blood pressure and augmented pulse pressure. The effects of biological sex on cardiovascular pathophysiology have long been known. The incidence of hypertension is higher in men, and it increases in postmenopausal women. Premenopausal women are protected from CVD compared with age-matched men and this protective effect is lost with menopause, suggesting that sex-hormones influence blood pressure regulation. In parallel, the heart progressively remodels over the course of life and the pattern of cardiac remodeling also differs between the sexes. Lower autonomic tone, reduced baroreceptor response, and greater vascular function are observed in premenopausal women than men of similar age. However, postmenopausal women have stiffer arteries than their male counterparts. The biological mechanisms responsible for sex-related differences observed in cardiovascular aging are being unraveled over the last several decades. This review focuses on molecular mechanisms underlying the sex-differences of CVD in aging.

Structure of a backtracked hexasomal intermediate of nucleosome transcription

During gene transcription, RNA polymerase II (RNA Pol II) passes nucleosomes with the help of various elongation factors. Here, we show that RNA Pol II achieves efficient nucleosome passage when the human elongation factors DSIF, PAF1 complex (PAF), RTF1, SPT6, and TFIIS are present. The cryo-EM structure of an intermediate of the nucleosome passage shows a partially unraveled hexasome that lacks the proximal H2A-H2B dimer and interacts with the RNA Pol II jaw, DSIF, and the CTR9trestle helix. RNA Pol II adopts a backtracked state with the RNA 3' end dislodged from the active site and bound in the RNA Pol II pore. Additional structures and biochemical data show that human TFIIS enters the RNA Pol II pore and stimulates the cleavage of the backtracked RNA and nucleosome passage.

KDM4C Contributes to Trophoblast-Like Stem Cell Conversion from Porcine-Induced Pluripotent Stem Cells (piPSCs) Via Regulating CDX2

Studies on ESRRB-regulating porcine-induced pluripotent stem cells (piPSCs) converted to trophoblast-like stem cells (TLSCs) contribute to the understanding of early embryo development. However, the epigenetic modification regulation network during the conversion is poorly understood. Here, the global change in histone H3 Lysine 4, 9, 27, 36 methylation and Lysine 27 acetylation was investigated in piPSCs and TLSCs. We found a high modification profile of H3K36me2 in TLSCs compared to that of piPSCs, whereas the profiles of other modifications remained constant. KDM4C, a H3K36me3/2 demethylase, whose gene body region was combined with ESRRB, was upregulated in TLSCs. Moreover, KDM4 inhibitor supplementation rescued the AP-negative phenotype observed in TLSCs, confirming that KDM4C could regulate the pluripotency of TLSCs. Subsequently, KDM4C replenishment results show the significantly repressed proliferation and AP-positive staining of TLSCs. The expressions of CDX2 and KRT8 were also upregulated after KDM4C overexpression. In summary, these results show that KDM4C replaced the function of ESRRB. These findings reveal the unique and crucial role of KDM4C-mediated epigenetic chromatin modifications in determination of piPSCs’ fate and expand the understanding of the connection between piPSCs and TSCs.

Free Energy Landscape of H2A-H2B Displacement From Nucleosome

Nucleosome reconstitution plays an important role in many cellular functions. As an initial step, H2A-H2B dimer displacement, which is accompanied by disruption of many of the interactions within the nucleosome, should occur. To understand how H2A-H2B dimer displacement occurs, an adaptively biased molecular dynamics (ABMD) simulation was carried out to generate a variety of displacements of the H2A-H2B dimer from the fully wrapped to partially unwrapped nucleosome structures. With regards to these structures, the free energy landscape of the dimer displacement was investigated using umbrella sampling simulations. We found that the main contributors to the free energy were the docking domain of H2A and the C-terminal of H4. There were various paths for the dimer displacement which were dependent on the extent of nucleosomal DNA wrapping, suggesting that modulation of the intra-nucleosomal interaction by external factors such as histone chaperons could control the path for the H2A-H2B dimer displacement. Key residues which contributed to the free energy have also been reported to be involved in the mutations and posttranslational modifications (PTMs) which are important for assembling and/or reassembling the nucleosome at the molecular level and are found in cancer cells at the phenotypic level. Our results give insight into how the H2A-H2B dimer displacement proceeds along various paths according to different interactions within the nucleosome.

The Fatal Circle of NETs and NET-Associated DAMPs Contributing to Organ Dysfunction

The innate immune system is the first line of defense against invading pathogens or sterile injuries. Pattern recognition receptors (PRR) sense molecules released from inflamed or damaged cells, or foreign molecules resulting from invading pathogens. PRRs can in turn induce inflammatory responses, comprising the generation of cytokines or chemokines, which further induce immune cell recruitment. Neutrophils represent an essential factor in the early immune response and fulfill numerous tasks to fight infection or heal injuries. The release of neutrophil extracellular traps (NETs) is part of it and was originally attributed to the capture and elimination of pathogens. In the last decade studies revealed a detrimental role of NETs during several diseases, often correlated with an exaggerated immune response. Overwhelming inflammation in single organs can induce remote organ damage, thereby further perpetuating release of inflammatory molecules. Here, we review recent findings regarding damage-associated molecular patterns (DAMPs) which are able to induce NET formation, as well as NET components known to act as DAMPs, generating a putative fatal circle of inflammation contributing to organ damage and sequentially occurring remote organ injury.

Emerging Functions of lncRNA Loci beyond the Transcript Itself

Thousands of long noncoding RNAs (lncRNAs) are actively transcribed in mammalian genomes. This class of RNAs has important regulatory functions in a broad range of cellular processes and diseases. Numerous lncRNAs have been demonstrated to mediate gene regulation through RNA-based mechanisms. Simultaneously, non-functional lncRNA transcripts derived from the activity of lncRNA loci have been identified, which underpin the notion that a considerable fraction of lncRNA loci exert regulatory functions through mechanisms associated with the production or the activity of lncRNA loci beyond the synthesized transcripts. We particularly distinguish two main RNA-independent components associated with regulatory effects; the act of transcription and the activity of DNA regulatory elements. We describe the experimental approaches to distinguish and understand the functional mechanisms derived from lncRNA loci. These scenarios reveal emerging mechanisms important to understanding the lncRNA implications in genome biology.

Inhibition of histone H3-H4 chaperone pathways rescues C. elegans sterility by H2B loss

Oncohistone mutations are crucial drivers for tumorigenesis, but how a living organism governs the loss-of-function oncohistone remains unclear. We generated a histone H2B triple knockout (3KO) strain in Caenorhabditis elegans, which decreased the embryonic H2B, disrupted cell divisions, and caused animal sterility. By performing genetic suppressor screens, we uncovered that mutations defective in the histone H3-H4 chaperone UNC-85 restored H2B 3KO fertility by decreasing chromatin H3-H4 levels. RNA interference of other H3-H4 chaperones or H3 or H4 histones also rescued H2B 3KO sterility. We showed that blocking H3-H4 chaperones recovered cell division in C. elegans carrying the oncohistone H2BE74K mutation that distorts the H2B-H4 interface and induces nucleosome instability. Our results indicate that reducing chromatin H3-H4 rescues the dysfunctional H2B in vivo and suggest that inhibiting H3-H4 chaperones may provide an effective therapeutic strategy for treating cancers resulting from loss-of-function H2B oncohistone.

SAFA facilitates chromatin opening of immune genes through interacting with anti-viral host RNAs

Regulation of chromatin structure and accessibility determines the transcription activities of genes, which endows the host with function-specific patterns of gene expression. Upon viral infection, the innate immune responses provide the first line of defense, allowing rapid production of variegated antiviral cytokines. Knowledge on how chromatin accessibility is regulated during host defense against viral infection remains limited. Our previous work found that the nuclear matrix protein SAFA surveilled viral RNA and regulated antiviral immune genes expression. However, how SAFA regulates the specific induction of antiviral immune genes remains unknown. Here, through integration of RNA-seq, ATAC-seq and ChIP-seq assays, we found that the depletion of SAFA specifically decreased the chromatin accessibility, activation and expression of virus induced genes. And mutation assays suggested that the RNA-binding ability of SAFA was essential for its function in regulating antiviral chromatin accessibility. RIP-seq results showed that SAFA exclusively bound with antiviral related RNAs following viral infection. Further, we combined the CRISPR-Cas13d mediated RNA knockdown system with ATAC-qPCR, and demonstrated that the binding between SAFA and according antiviral RNAs specifically mediated the openness of the corresponding chromatin and following robust transcription of antiviral genes. Moreover, knockdown of these associated RNAs dampened the accessibility of related genes in an extranuclear signaling pathway dependent manner. Interestingly, VSV infection cleaved SAFA protein at the C-terminus which deprived its RNA binding ability for immune evasion. Thus, our results demonstrated that SAFA and the interacting RNA products collaborated and remodeled chromatin accessibility to facilitate antiviral innate immune responses.

Regulation of chromatin opening and gene expression underlies a key point during host defense against viral infection, which endows the host with timely and effective antiviral gene expression patterns. We previously reported that the nuclear matrix protein SAFA surveils viral RNA and regulates antiviral immune genes expression. However, how SAFA regulates the expression and what determines the specific induction of antiviral immune genes remains unclear. Here, we used a combination of high-throughput sequencing technologies and found that SAFA and the interacting RNA products collaborated and specifically remodeled chromatin accessibility to facilitate antiviral immune genes expression. We also found that VSV infection cleaved SAFA protein at the C-terminus and deprived its RNA binding ability for immune evasion. Our study provides new insights into the mechanism by which chromatin remodeling facilitates the induction of antiviral immune genes.

Cooperation between intrinsically disordered and ordered regions of Spt6 regulates nucleosome and Pol II CTD binding, and nucleosome assembly

Transcription elongation factor Spt6 associates with RNA polymerase II (Pol II) and acts as a histone chaperone, which promotes the reassembly of nucleosomes following the passage of Pol II. The precise mechanism of nucleosome reassembly mediated by Spt6 remains unclear. In this study, we used a hybrid approach combining cryo-electron microscopy and small-angle X-ray scattering to visualize the architecture of Spt6 from Saccharomyces cerevisiae. The reconstructed overall architecture of Spt6 reveals not only the core of Spt6, but also its flexible N- and C-termini, which are critical for Spt6's function. We found that the acidic N-terminal region of Spt6 prevents the binding of Spt6 not only to the Pol II CTD and Pol II CTD-linker, but also to pre-formed intact nucleosomes and nucleosomal DNA. The N-terminal region of Spt6 self-associates with the tSH2 domain and the core of Spt6 and thus controls binding to Pol II and nucleosomes. Furthermore, we found that Spt6 promotes the assembly of nucleosomes in vitro. These data indicate that the cooperation between the intrinsically disordered and structured regions of Spt6 regulates nucleosome and Pol II CTD binding, and also nucleosome assembly.

H2A.Z's 'social' network: functional partners of an enigmatic histone variant

The histone variant H2A.Z has been extensively studied to understand its manifold DNA-based functions. In the past years, researchers identified its specific binding partners, the 'H2A.Z interactome', that convey H2A.Z-dependent chromatin changes. Here, we summarize the latest findings regarding vertebrate H2A.Z-associated factors and focus on their roles in gene activation and repression, cell cycle regulation, (neuro)development, and tumorigenesis. Additionally, we demonstrate how protein-protein interactions and post-translational histone modifications can fine-tune the complex interplay of H2A.Z-regulated gene expression. Last, we review the most recent results on interactors of the two isoforms H2A.Z.1 and H2A.Z.2.1, which differ in only three amino acids, and focus on cancer-associated mutations of H2A and H2A.Z, which reveal fascinating insights into the functional importance of such minuscule changes.

Spn1 and its dynamic interactions with Spt6, histones and nucleosomes

Histone chaperones facilitate the assembly and disassembly of nucleosomes and regulate DNA accessibility for critical cellular processes. Spn1 is an essential, highly conserved histone chaperone that functions in transcription initiation and elongation in a chromatin context. Here we demonstrate that Spn1 binds H3-H4 with low nanomolar affinity, residues 85-99 within the acidic N-terminal region of Spn1 are required for H3-H4 binding, and Spn1 binding to H3-H4 dimers does not impede (H3-H4)₂ tetramer formation. Previous work has shown the central region of Spn1 (residues 141-305) is important for interaction with Spt6, another conserved and essential histone chaperone. We show that the C-terminal region of Spn1 also contributes to Spt6 binding and is critical for Spn1 binding to nucleosomes. We also show Spt6 preferentially binds H3-H4 tetramers and Spt6 competes with nucleosomes for Spn1 binding. Combined with previous results, this indicates the Spn1-Spt6 complex does not bind nucleosomes. In contrast to nucleosome binding, we found that the Spn1-Spt6 complex can bind H3-H4 dimers and tetramers and H2A-H2B to form ternary complexes. These important results provide new information about the functions of Spn1, Spt6, and the Spn1-Spt6 complex, two essential and highly conserved histone chaperones.

Twist2-driven chromatin remodeling governs the postnatal maturation of dermal fibroblasts

Dermal fibroblasts lose stem cell potency after birth, which prevents regenerative healing. However, the underlying intracellular mechanisms are largely unknown. We uncover the postnatal maturation of papillary fibroblasts (PFs) driven by the extensive Twist2-mediated remodeling of chromatin accessibility. A loss of the regenerative ability of postnatal PFs occurs with decreased H3K27ac levels. Single-cell transcriptomics, assay for transposase-accessible chromatin sequencing (ATAC-seq), and chromatin immunoprecipitation sequencing (ChIP-seq) reveal the postnatal maturation trajectory associated with the loss of the regenerative trajectory in PFs, which is characterized by a marked decrease in chromatin accessibility and H3K27ac modifications. Histone deacetylase inhibition delays spontaneous chromatin remodeling, thus maintaining the regenerative ability of postnatal PFs. Genomic analysis identifies Twist2 as a major regulator within chromatin regions with decreased accessibility during the postnatal period. When Twist2 is genetically deleted in dermal fibroblasts, the intracellular cascade of postnatal maturation is significantly delayed. Our findings reveal the comprehensive intracellular mechanisms underlying intrinsic postnatal changes in dermal fibroblasts.

Stable inheritance of H3.3-containing nucleosomes during mitotic cell divisions

Newly synthesized H3.1 and H3.3 histones are assembled into nucleosomes by different histone chaperones in replication-coupled and replication-independent pathways, respectively. However, it is not clear how parental H3.3 molecules are transferred following DNA replication, especially when compared to H3.1. Here, by monitoring parental H3.1- and H3.3-SNAP signals, we show that parental H3.3, like H3.1, are stably transferred into daughter cells. Moreover, Mcm2-Pola1 and Pole3-Pole4, two pathways involved in parental histone transfer based upon the analysis of modifications on parental histones, participate in the transfer of both H3.1 and H3.3 following DNA replication. Lastly, we found that Mcm2, Pole3 and Pole4 mutants defective in parental histone transfer show defects in chromosome segregation. These results indicate that in contrast to deposition of newly synthesized H3.1 and H3.3, transfer of parental H3.1 and H3.3 is mediated by these shared mechanisms, which contributes to epigenetic memory of gene expression and maintenance of genome stability.

How nucleosome assembly of parental histones is regulated following DNA replication is still an open question. Here the authors show that unlike deposition of new histones H3.1 and H3.3 that utilizes different histone chaperones, parental H3.1 and H3.3 are both stably inherited during mitotic cell division in mouse embryonic stem cells, and this involves histone chaperones Mcm2, Pole3 and Pole4.

Gigantic genomes of salamanders indicate that body temperature, not genome size, is the driver of global methylation and 5-methylcytosine deamination in vertebrates

Transposable elements (TEs) are sequences that replicate and move throughout genomes, and they can be silenced through methylation of cytosines at CpG dinucleotides. TE abundance contributes to genome size, but TE silencing variation across genomes of different sizes remains underexplored. Salamanders include most of the largest C-values - 9 to 120 Gb. We measured CpG methylation levels in salamanders with genomes ranging from 2N = ∼58 Gb to 4N = ∼116 Gb. We compared these levels to results from endo- and ectothermic vertebrates with more typical genomes. Salamander methylation levels are approximately 90%, higher than all endotherms. However, salamander methylation does not differ from other ectotherms, despite an approximately 100-fold difference in nuclear DNA content. Because methylation affects the nucleotide compositional landscape through 5-methylcytosine deamination to thymine, we quantified salamander CpG dinucleotide levels and compared them to other vertebrates. Salamanders and other ectotherms have comparable CpG levels, and ectotherm levels are higher than endotherms. These data show no shift in global methylation at the base of salamanders, despite a dramatic increase in TE load and genome size. This result is reconcilable with previous studies that considered endothermy and ectothermy, which may be more important drivers of methylation in vertebrates than genome size.

Histone Modifications, Internucleosome Dynamics, and DNA Stresses: How They Cooperate to “Functionalize” Nucleosomes

Tight packaging of DNA in chromatin severely constrains DNA accessibility and dynamics. In contrast, nucleosomes in active chromatin state are highly flexible, can exchange their histones, and are virtually “transparent” to RNA polymerases, which transcribe through gene bodies at rates comparable to that of naked DNA. Defining mechanisms that revert nucleosome repression, in addition to their value for basic science, is of key importance for the diagnosis and treatment of genetic diseases. Chromatin activity is largely regulated by histone posttranslational modifications, ranging from small chemical groups up to the yet understudied “bulky” ubiquitylation and sumoylation. However, it is to be revealed how histone marks are “translated” to permissive or repressive changes in nucleosomes: it is a general opinion that histone modifications act primarily as “signals” for recruiting the regulatory proteins or as a “neutralizer” of electrostatic shielding of histone tails. Here, we would like to discuss recent evidence suggesting that histone ubiquitylation, in a DNA stress–dependent manner, can directly regulate the dynamics of the nucleosome and their primary structure and can promote nucleosome decomposition to hexasome particles or additionally stabilize nucleosomes against unwrapping. In addition, nucleosome repression/ derepression studies are usually performed with single mononucleosomes as a model. We would like to review and discuss recent findings showing that internucleosomal interactions could strongly modulate the dynamics and rearrangements of nucleosomes. Our hypothesis is that bulky histone modifications, nucleosome inherent dynamics, internucleosome interactions, and DNA torsions could act in cooperation to orchestrate the formation of different dynamic states of arrayed nucleosomes and thus promote chromatin functionality and diversify epigenetic programming methods.

Antisense-mediated repression of SAGA-dependent genes involves the HIR histone chaperone

Eukaryotic genomes are pervasively transcribed by RNA polymerase II (RNAPII), and transcription of long non-coding RNAs often overlaps with coding gene promoters. This might lead to coding gene repression in a process named Transcription Interference (TI). In Saccharomyces cerevisiae, TI is mainly driven by antisense non-coding transcription and occurs through re-shaping of promoter Nucleosome-Depleted Regions (NDRs). In this study, we developed a genetic screen to identify new players involved in Antisense-Mediated Transcription Interference (AMTI). Among the candidates, we found the HIR histone chaperone complex known to be involved in de novo histone deposition. Using genome-wide approaches, we reveal that HIR-dependent histone deposition represses the promoters of SAGA-dependent genes via antisense non-coding transcription. However, while antisense transcription is enriched at promoters of SAGA-dependent genes, this feature is not sufficient to define the mode of gene regulation. We further show that the balance between HIR-dependent nucleosome incorporation and transcription factor binding at promoters directs transcription into a SAGA- or TFIID-dependent regulation. This study sheds light on a new connection between antisense non-coding transcription and the nature of coding transcription initiation.

HDAC6 regulates NF-κB signalling to control chondrocyte IL-1-induced MMP and inflammatory gene expression

Elevated pro-inflammatory signalling coupled with catabolic metalloproteinase expression is a common feature of arthritis, leading to cartilage damage, deterioration of the joint architecture and the associated pain and immobility. Countering these processes, histone deacetylase inhibitors (HDACi) have been shown to suppress matrix metalloproteinase (MMP) expression, block cytokine-induced signalling and reduce the cartilage degradation in animal models of the arthritis. In order to establish which specific HDACs account for these chondro-protective effects an HDAC1-11 RNAi screen was performed. HDAC6 was required for both the interleukin (IL)-1 induction of MMP expression and pro-inflammatory interleukin expression in chondrocytes, implicating an effect on NF-κB signalling. Depletion of HDAC6 post-transcriptionally up-regulated inhibitor of κB (IκB), prevented the nuclear translocation of NF-κB subunits and down-regulated NF-κB reporter activation. The pharmacological inhibition of HDAC6 reduced MMP expression in chondrocytes and cartilage collagen release. This work highlights the important role of HDAC6 in pro-inflammatory signalling and metalloproteinase gene expression, and identifies a part for HDAC6 in the NF-κB signalling pathway. By confirming the protection of cartilage this work supports the inhibition of HDAC6 as a possible therapeutic strategy in arthritis.

Global 5mC and 5hmC DNA Levels in Human Sperm Subpopulations with Differentially Protaminated Chromatin in Normo- and Oligoasthenozoospermic Males

Epigenetic modifications play a special role in the male infertility aetiology. Published data indicate the link between sperm quality and sperm chromatin protamination. This study aimed to determine the relationship between methylation (5mC) and hydroxymethylation (5hmC) in sperm DNA, with respect to sperm chromatin protamination in three subpopulations of fertile normozoospermic controls and infertile patients with oligo-/oligoasthenozoospermia. For the first time, a sequential staining protocol was applied, which allowed researchers to analyse 5mC/5hmC levels by immunofluorescence staining, with a previously determined chromatin protamination status (aniline blue staining), using the same spermatozoa. TUNEL assay determined the sperm DNA fragmentation level. The 5mC/5hmC levels were diversified with respect to chromatin protamination status in both studied groups of males, with the highest values observed in protaminated spermatozoa. The linkage between chromatin protamination and 5mC/5hmC levels in control males disappeared in patients with deteriorated semen parameters. A relationship between 5mC/5hmC and sperm motility/morphology was identified in the patient group. Measuring the 5mC/5hmC status of sperm DNA according to sperm chromatin integrity provides evidence of correct spermatogenesis, and its disruption may represent a prognostic marker for reproductive failure.

SWI/SNF and the histone chaperone Rtt106 drive expression of the Pleiotropic Drug Resistance network genes

The Pleiotropic Drug Resistance (PDR) network is central to the drug response in fungi, and its overactivation is associated with drug resistance. However, gene regulation of the PDR network is not well understood. Here, we show that the histone chaperone Rtt106 and the chromatin remodeller SWI/SNF control expression of the PDR network genes and confer drug resistance. In Saccharomyces cerevisiae, Rtt106 specifically localises to PDR network gene promoters dependent on transcription factor Pdr3, but not Pdr1, and is essential for Pdr3-mediated basal expression of the PDR network genes, while SWI/SNF is essential for both basal and drug-induced expression. Also in the pathogenic fungus Candida glabrata, Rtt106 and SWI/SNF regulate drug-induced PDR gene expression. Consistently, loss of Rtt106 or SWI/SNF sensitises drug-resistant S. cerevisiae mutants and C. glabrata to antifungal drugs. Since they cooperatively drive PDR network gene expression, Rtt106 and SWI/SNF represent potential therapeutic targets to combat antifungal resistance.

Phosphorylated MED1 links transcription recycling and cancer growth

Mediator activates RNA polymerase II (Pol II) function during transcription, but it remains unclear whether Mediator is able to travel with Pol II and regulate Pol II transcription beyond the initiation and early elongation steps. By using in vitro and in vivo transcription recycling assays, we find that human Mediator 1 (MED1), when phosphorylated at the mammal-specific threonine 1032 by cyclin-dependent kinase 9 (CDK9), dynamically moves along with Pol II throughout the transcribed genes to drive Pol II recycling after the initial round of transcription. Mechanistically, MED31 mediates the recycling of phosphorylated MED1 and Pol II, enhancing mRNA output during the transcription recycling process. Importantly, MED1 phosphorylation increases during prostate cancer progression to the lethal phase, and pharmacological inhibition of CDK9 decreases prostate tumor growth by decreasing MED1 phosphorylation and Pol II recycling. Our results reveal a novel role of MED1 in Pol II transcription and identify phosphorylated MED1 as a targetable driver of dysregulated Pol II recycling in cancer.

Human cytomegalovirus lytic infection inhibits replication-dependent histone synthesis and requires stem loop binding protein function

Until now, it was not known if, how, or why pathogenic human viruses might modulate the de novo production of the replication-dependent (RD) histone proteins that decorate their DNA genomes within infected cells. Our finding that human cytomegalovirus (HCMV) inhibits RD histone production affirms that a virus targets this fundamental cellular process. Furthermore, our revelation that HCMV induces, relocalizes, and then commandeers the stem loop–binding protein (SLBP) for a purpose other than RD histone synthesis to support productive replication illuminates the potential for other functions of this highly conserved protein. The critical nature of SLBP for HCMV infection and of RD histone synthesis for cellular DNA replication highlights this process as a target for future antiviral and chemotherapeutic interventions.

Replication-dependent (RD) histones are deposited onto human cytomegalovirus (HCMV) genomes at the start of infection. We examined how HCMV affects the de novo production of RD histones and found that viral infection blocked the accumulation of RD histone mRNAs that normally occurs during the S phase. Furthermore, RD histone mRNAs present in HCMV-infected cells did not undergo the unique 3′ processing required for their normal nuclear export and translation. The protein that orchestrates processing in the nucleus, stem loop–binding protein (SLBP), was found predominantly in the cytoplasm, and RD histone proteins were not de novo synthesized in HCMV-infected cells. Intriguingly, however, we found that SLBP was required for the efficient synthesis and assembly of infectious progeny virions. We conclude that HCMV infection attenuates RD histone mRNA accumulation and processing and the de novo protein synthesis of the RD histones, while utilizing SLBP for an alternative purpose to support infectious virion production.

The histone variant macroH2A1.1 regulates RNA Polymerase II paused genes within defined chromatin interaction landscapes

The histone variant macroH2A1.1 plays a role in cancer development and metastasis. To determine the underlying molecular mechanisms, we mapped the genome-wide localization of endogenous macroH2A1.1 in the human breast cancer cell line MDA-MB-231. We demonstrate that macroH2A1.1 specifically binds to active promoters and enhancers in addition to facultative heterochromatin. Selective knock down of macroH2A1.1 deregulates the expression of hundreds of highly active genes. Depending on the chromatin landscape, macroH2A1.1 acts through two distinct molecular mechanisms. The first mitigates excessive transcription by binding over domains including the promoter and the gene body. The second stimulates expression of RNA polymerase II (Pol II)-paused genes, including genes regulating mammary tumor cell migration. In contrast to the first mechanism, macroH2A1.1 specifically associates with the transcription start site of Pol II-paused genes. These processes occur in a predefined local 3D genome landscape, but do not require rewiring of enhancer-promoter contacts. We thus propose that macroH2A1.1 serves as a transcriptional modulator with a potential role in assisting the conversion of promoter-locked Pol II into a productive, elongating Pol II.

Summary: Histone variant macroH2A1.1 binding to the TSS of genes dependent on Pol II pausing stimulates transcription by promoting Pol II release in a human triple-negative breast cancer cell model.

Epigenetic remodelling in human hepatocellular carcinoma

Hepatocellular carcinoma (HCC) is the most frequent primary liver cancer, being the sixth most commonly diagnosed cancer and the fourth leading cause of cancer-related death. As other heterogeneous solid tumours, HCC results from a unique synergistic combination of genetic alterations mixed with epigenetic modifications.In HCC the patterns and frequencies of somatic variations change depending on the nearby chromatin. On the other hand, epigenetic alterations often induce genomic instability prone to mutations. Epigenetics refers to heritable states of gene expression without alteration to the DNA sequence itself and, unlike genetic changes, the epigenetic modifications are reversible and affect gene expression more extensively than genetic changes. Thus, studies of epigenetic regulation and the involved molecular machinery are greatly contributing to the understanding of the mechanisms that underline HCC onset and heterogeneity. Moreover, this knowledge may help to identify biomarkers for HCC diagnosis and prognosis, as well as future new targets for more efficacious therapeutic approaches.In this comprehensive review we will discuss the state-of-the-art knowledge about the epigenetic landscape in hepatocarcinogenesis, including evidence on the diagnostic and prognostic role of non-coding RNAs, modifications occurring at the chromatin level, and their role in the era of precision medicine.Apart from other better-known risk factors that predispose to the development of HCC, characterization of the epigenetic remodelling that occurs during hepatocarcinogenesis could open the way to the identification of personalized biomarkers. It may also enable a more accurate diagnosis and stratification of patients, and the discovery of new targets for more efficient therapeutic approaches.

Epigenetic regulation of human non-coding RNA gene transcription

Recent investigations on the non-protein-coding transcriptome of human cells have revealed previously hidden layers of gene regulation relying on regulatory non-protein-coding (nc) RNAs, including the widespread ncRNA-dependent regulation of epigenetic chromatin states and of mRNA translation and stability. However, despite its centrality, the epigenetic regulation of ncRNA genes has received relatively little attention. In this mini-review, we attempt to provide a synthetic account of recent literature suggesting an unexpected complexity in chromatin-dependent regulation of ncRNA gene transcription by the three human nuclear RNA polymerases. Emerging common features, like the heterogeneity of chromatin states within ncRNA multigene families and their influence on 3D genome organization, point to unexplored issues whose investigation could lead to a better understanding of the whole human epigenomic network.

Coordinated DNA and histone dynamics drive accurate histone H2A.Z exchange

Nucleosomal histone H2A is exchanged for its variant H2A.Z by the SWR1 chromatin remodeler, but the mechanism and timing of histone exchange remain unclear. Here, we quantify DNA and histone dynamics during histone exchange in real time using a three-color single-molecule FRET assay. We show that SWR1 operates with timed precision to unwrap DNA with large displacement from one face of the nucleosome, remove H2A-H2B from the same face, and rewrap DNA, all within 2.3 s. This productive DNA unwrapping requires full SWR1 activation and differs from unproductive, smaller-scale DNA unwrapping caused by SWR1 binding alone. On an asymmetrically positioned nucleosome, SWR1 intrinsically senses long-linker DNA to preferentially exchange H2A.Z on the distal face as observed in vivo. The displaced H2A-H2B dimer remains briefly associated with the SWR1-nucleosome complex and is dissociated by histone chaperones. These findings reveal how SWR1 coordinates DNA unwrapping with histone dynamics to rapidly and accurately place H2A.Z at physiological sites on chromatin.

CaSWC4 regulates the immunity-thermotolerance tradeoff by recruiting CabZIP63/CaWRKY40 to target genes and activating chromatin in pepper

Pepper (Capsicum annuum) responds differently to high temperature stress (HTS) and Ralstonia solanacearum infection (RSI) but employs some shared transcription factors (TFs), such as CabZIP63 and CaWRKY40, in both cases. How the plant activates and balances these distinct responses, however, was unclear. Here, we show that the protein CaSWC4 interacts with CaRUVBL2 and CaTAF14b and they all act positively in pepper response to RSI and thermotolerance. CaSWC4 activates chromatin of immunity or thermotolerance related target genes of CaWRKY40 or CabZIP63 by promoting deposition of H2A.Z, H3K9ac and H4K5ac, simultaneously recruits CabZIP63 and CaWRKY40 through physical interaction and brings them to their targets (immunity- or thermotolerance-related genes) via binding AT-rich DNA element. The above process relies on the recruitment of CaRUVBL2 and TAF14 by CaSWC4 via physical interaction, which occurs at loci of immunity related target genes only when the plants are challenged with RSI, and at loci of thermotolerance related target genes only upon HTS. Collectively, our data suggest that CaSWC4 regulates rapid, accurate responses to both RSI and HTS by modulating chromatin of specific target genes opening and recruiting the TFs, CaRUVBL2 and CaTAF14b to the specific target genes, thereby helping achieve the balance between immunity and thermotolerance.

Functional Domains of the Early Proteins and Experimental and Epidemiological Studies Suggest a Role for the Novel Human Polyomaviruses in Cancer

As their name indicates, polyomaviruses (PyVs) can induce tumors. Mouse PyV, hamster PyV and raccoon PyV have been shown to cause tumors in their natural host. During the last 30 years, 15 PyVs have been isolated from humans. From these, Merkel cell PyV is classified as a Group 2A carcinogenic pathogen (probably carcinogenic to humans), whereas BKPyV and JCPyV are class 2B (possibly carcinogenic to humans) by the International Agency for Research on Cancer. Although the other PyVs recently detected in humans (referred to here as novel HPyV; nHPyV) share many common features with PyVs, including the viral oncoproteins large tumor antigen and small tumor antigen, as their role in cancer is questioned. This review discusses whether the nHPyVs may play a role in cancer based on predicted and experimentally proven functions of their early proteins in oncogenic processes. The functional domains that mediate the oncogenic properties of early proteins of known PyVs, that can cause cancer in their natural host or animal models, have been well characterized and we examined whether these functional domains are conserved in the early proteins of the nHPyVs and presented experimental evidence that these conserved domains are functional. Furthermore, we reviewed the literature describing the detection of nHPyV in human tumors.

The Role of Epigenetic Mechanisms in Autoimmune, Neurodegenerative, Cardiovascular, and Imprinting Disorders

Epigenetic mutations like aberrant DNA methylation, histone modifications, or RNA silencing are found in a number of human diseases. This review article discusses the epigenetic mechanisms involved in neurodegenerative disorders, cardiovascular disorders, auto-immune disorder, and genomic imprinting disorders. In addition, emerging epigenetic therapeutic strategies for the treatment of such disorders are presented. Medicinal chemistry campaigns highlighting the efforts of the chemists invested towards the rational design of small molecule inhibitors have also been included. Pleasingly, several classes of epigenetic inhibitors, DNMT, HDAC, BET, HAT, and HMT inhibitors along with RNA based therapies have exhibited the potential to emerge as therapeutics in the longer run. It is quite hopeful that epigenetic modulator-based therapies will advance to clinical stage investigations by leaps and bounds.

SETD2 loss perturbs the kidney cancer epigenetic landscape to promote metastasis and engenders actionable dependencies on histone chaperone complexes

SETD2 is a H3K36 trimethyltransferase that is mutated with high prevalence (13%) in clear cell renal cell carcinoma (ccRCC). Genomic profiling of primary ccRCC tumors reveals a positive correlation between SETD2 mutations and metastasis. However, whether and how SETD2 loss promotes metastasis remains unclear. In this study, we used SETD2-mutant metastatic ccRCC patient-derived cell line and xenograft models and showed that H3K36me3 restoration greatly reduced distant metastases of ccRCC in mice in an MMP1-dependent manner. An integrated multi-omics analysis using ATAC-seq, ChIP-seq, and RNA-seq established a tumor suppressor model in which loss of SETD2-mediated H3K36me3 activates enhancers to drive oncogenic transcriptional output through regulation of chromatin accessibility. Furthermore, we uncovered mechanism-based therapeutic strategies for SETD2-deficient cancer through the targeting of specific histone chaperone complexes including ASF1A/B and SPT16. Overall, SETD2 loss creates a permissive epigenetic landscape for cooperating oncogenic drivers to amplify transcriptional output, providing unique therapeutic opportunities.

DNA Double Strand Break Repair and Its Control by Nucleosome Remodeling

DNA double strand breaks (DSBs) are repaired in eukaryotes by one of several cellular mechanisms. The decision-making process controlling DSB repair takes place at the step of DNA end resection, the nucleolytic processing of DNA ends, which generates single-stranded DNA overhangs. Dependent on the length of the overhang, a corresponding DSB repair mechanism is engaged. Interestingly, nucleosomes-the fundamental unit of chromatin-influence the activity of resection nucleases and nucleosome remodelers have emerged as key regulators of DSB repair. Nucleosome remodelers share a common enzymatic mechanism, but for global genome organization specific remodelers have been shown to exert distinct activities. Specifically, different remodelers have been found to slide and evict, position or edit nucleosomes. It is an open question whether the same remodelers exert the same function also in the context of DSBs. Here, we will review recent advances in our understanding of nucleosome remodelers at DSBs: to what extent nucleosome sliding, eviction, positioning and editing can be observed at DSBs and how these activities affect the DSB repair decision.

Genetics, Epigenetics, Cellular Immunology, and Gut Microbiota: Emerging Links With Graves' Disease

Graves’ disease (GD) is a well-known organ-specific autoimmune disease characterized by hyperthyroidism, goiter, and exophthalmos. The incidence of GD is approximately 2.0–3.0% in China and 0.5–2.0% in Western countries. Due to the complex pathogenesis and etiology of GD, current treatment methods have great side effects that seriously endanger human health. Therefore, it is particularly important to understand the pathogenesis of GD. Various studies have shown that genetics, epigenetics, cellular immunology, and gut microbiota are all involved in the development of GD. Genetically, CD25 gene and VDR gene polymorphisms are involved in the development of GD by increasing the ratio of Th17/Treg cells. Epigenetically, miR-23a-3p and lncRNA-MEG3 lead to Th17/Treg imbalance and participate in the progression of GD. Moreover, commensal microbe deletion can disrupt Th17/Treg balance and participate in the occurrence of GD. The imbalance of Th17/Treg cells induced by genetics, epigenetics, and gut microbiota plays a vital role in the pathogenesis of GD. Therefore, this article reviews the role of genetics, epigenetics, cellular immunology, and gut microbiota in the pathogenic mechanism of GD. This may lead to the development of novel therapeutic strategies and providing promising therapeutic targets.

E2F and STAT3 provide transcriptional synergy for histone variant H2AZ activation to sustain glioblastoma chromatin accessibility and tumorigenicity

The histone variant H2AZ is overexpressed in diverse cancer types where it facilitates the accessibility of transcriptional regulators to the promoters of cell cycle genes. However, the molecular basis for its dysregulation in cancer remains unknown. Here, we report that glioblastomas (GBM) and glioma stem cells (GSCs) preferentially overexpress H2AZ for their proliferation, stemness and tumorigenicity. Chromatin accessibility analysis of H2AZ2 depleted GSC revealed that E2F1 occupies the enhancer region within H2AZ2 gene promoter, thereby activating H2AZ2 transcription. Exploration of other H2AZ2 transcriptional activators using a customized "anti-H2AZ2" query signature for connectivity map analysis identified STAT3. Co-targeting E2F and STAT3 synergistically reduced the levels of H2AZ, histone 3 lysine 27 acetylation (H3K27ac) and cell cycle gene transcription, indicating that E2F1 and STAT3 synergize to activate H2AZ gene transcription in GSCs. Remarkably, an E2F/STAT3 inhibitor combination durably suppresses GSC tumorigenicity in an orthotopic GBM xenograft model. In glioma patients, high STAT3 signaling is associated with high E2F1 and H2AZ2 expression. Thus, GBM has uniquely opted the use of E2F1- and STAT3-containing "enhanceosomes" that integrate multiple signaling pathways to achieve H2AZ gene activation, supporting a translational path for the E2F/STAT3 inhibitor combination to be applied in GBM treatment.

Kynurenic Acid and Its Analog SZR104 Exhibit Strong Antiinflammatory Effects and Alter the Intracellular Distribution and Methylation Patterns of H3 Histones in Immunochallenged Microglia-Enriched Cultures of Newborn Rat Brains

Kynurenic acid (KYNA) is implicated in antiinflammatory processes in the brain through several cellular and molecular targets, among which microglia-related mechanisms are of paramount importance. In this study, we describe the effects of KYNA and one of its analogs, the brain-penetrable SZR104 (N-(2-(dimethylamino)ethyl)-3-(morpholinomethyl)-4-hydroxyquinoline-2-carboxamide), on the intracellular distribution and methylation patterns of histone H3 in immunochallenged microglia cultures. Microglia-enriched secondary cultures made from newborn rat forebrains were immunochallenged with lipopolysaccharide (LPS). The protein levels of selected inflammatory markers C–X–C motif chemokine ligand 10 (CXCL10) and C–C motif chemokine receptor 1 (CCR1), histone H3, and posttranslational modifications of histone H3 lys methylation sites (H3K9me3 and H3K36me2, marks typically associated with opposite effects on gene expression) were analyzed using quantitative fluorescent immunocytochemistry and western blots in control or LPS-treated cultures with or without KYNA or SZR104. KYNA and SZR104 reduced levels of the inflammatory marker proteins CXCL10 and CCR1 after LPS-treatment. Moreover, KYNA and SZR104 favorably affected histone methylation patterns as H3K9me3 and H3K36me2 immunoreactivities, and histone H3 protein levels returned toward control values after LPS treatment. The cytoplasmic translocation of H3K9me3 from the nucleus indicated inflammatory distress, a process that could be inhibited by KYNA and SZR104. Thus, KYNA signaling and metabolism, and especially brain-penetrable KYNA analogs such as SZR104, could be key targets in the pathway that connects chromatin structure and epigenetic mechanisms with functional consequences that affect neuroinflammation and perhaps neurodegeneration.

HIRA complex presets transcriptional potential through coordinating depositions of the histone variants H3.3 and H2A.Z on the poised genes in mESCs

Histone variants have been implicated in regulating chromatin dynamics and genome functions. Previously, we have shown that histone variant H3.3 actively marks enhancers and cooperates with H2A.Z at promoters to prime the genes into a poised state in mouse embryonic stem cells (mESCs). However, how these two important histone variants collaboratively function in this process still remains elusive. In this study, we found that depletion of different components of HIRA complex, a specific chaperone of H3.3, results in significant decreases of H2A.Z enrichment at genome scale. In addition, CUT&Tag data revealed a genomic colocalization between HIRA complex and SRCAP complex. In vivo and in vitro biochemical assays verified that HIRA complex could interact with SRCAP complex through the Hira subunit. Furthermore, our chromatin accessibility and transcription analyses demonstrated that HIRA complex contributed to preset a defined chromatin feature around TSS region for poising gene transcription. In summary, our results unveiled that while regulating the H3.3 incorporation in the regulatory regions, HIRA complex also collaborates with SRCAP to deposit H2A.Z onto the promoters, which cooperatively determines the transcriptional potential of the poised genes in mESCs.

Impact of Physical Activity and Exercise on the Epigenome in Skeletal Muscle and Effects on Systemic Metabolism

Exercise and physical activity induces physiological responses in organisms, and adaptations in skeletal muscle, which is beneficial for maintaining health and preventing and/or treating most chronic diseases. These adaptations are mainly instigated by transcriptional responses that ensue in reaction to each individual exercise, either resistance or endurance. Consequently, changes in key metabolic, regulatory, and myogenic genes in skeletal muscle occur as both an early and late response to exercise, and these epigenetic modifications, which are influenced by environmental and genetic factors, trigger those alterations in the transcriptional responses. DNA methylation and histone modifications are the most significant epigenetic changes described in gene transcription, linked to the skeletal muscle transcriptional response to exercise, and mediating the exercise adaptations. Nevertheless, other alterations in the epigenetics markers, such as epitranscriptomics, modifications mediated by miRNAs, and lactylation as a novel epigenetic modification, are emerging as key events for gene transcription. Here, we provide an overview and update of the impact of exercise on epigenetic modifications, including the well-described DNA methylations and histone modifications, and the emerging modifications in the skeletal muscle. In addition, we describe the effects of exercise on epigenetic markers in other metabolic tissues; also, we provide information about how systemic metabolism or its metabolites influence epigenetic modifications in the skeletal muscle.

Epigenetic alterations induced by genotoxic occupational and environmental human chemical carcinogens: An update of a systematic literature review

Epigenetic alterations, such as changes in DNA methylation, histones/chromatin structure, nucleosome positioning, and expression of non-coding RNAs, are recognized among key characteristics of carcinogens; they may occur independently or concomitantly with genotoxic effects. While data on genotoxicity are collected through standardized guideline tests, data collected on epigenetic effects is far less uniform. In 2016, we conducted a systematic review of published studies of genotoxic carcinogens that reported epigenetic endpoints to better understand the evidence for epigenetic alterations of human carcinogens, and the potential association with genotoxic endpoints. Since then, the number of studies of epigenetic effects of chemicals has nearly doubled. This review stands as an update on epigenetic alterations induced by occupational and environmental human carcinogens that were previously and recently classified as Group 1 by the International Agency for Research on Cancer. We found that the evidence of epigenetic effects remains uneven across agents. Studies of DNA methylation are most abundant, while reports concerning effects on non-coding RNA have increased over the past 5 years. By contrast, mechanistic toxicology studies of histone modifications and chromatin state alterations remain few. We found that most publications of epigenetic effects of carcinogens were studies in exposed humans or human cells. Studies in rodents represent the second most common species used for epigenetic studies in toxicology, in vivo exposures being the most predominant. Future studies should incorporate dose- and time-dependent study designs and also investigate the persistence of effects following cessation of exposure, considering the dynamic nature of most epigenetic alterations.

Discovery of Unknown Posttranslational Modifications by Top-Down Mass Spectrometry

Protein encoding genes can undergo modifications posttranscriptionally and posttranslationally, yielding many different "proteoforms." The chemical diversity of such modifications is known to be important biomarkers of function within biological systems but is not completely understood. Top-down mass spectrometry is a valuable tool for the characterization of proteoforms, especially for histones that have complex combinations of posttranslational modifications (PTMs). In this chapter, we present a top-down liquid chromatography-mass spectrometry experimental and data analysis workflow for the identification of novel, unexpected modifications on histones. Proteoforms of interest are first discovered using the "open" modification search in TopPIC. Then target proteoforms are manually confirmed using the data visualization tool-LcMsSpectator, part of the Informed-Proteomics package. The workflow can be very helpful in targeted PTM analysis and can be expanded to other types of proteins for discovery of unknown PTMs.

Chromatin Changes in Phytochrome Interacting Factor-Regulated Genes Parallel Their Rapid Transcriptional Response to Light

As sessile organisms, plants must adapt to a changing environment, sensing variations in resource availability and modifying their development in response. Light is one of the most important resources for plants, and its perception by sensory photoreceptors (e.g., phytochromes) and subsequent transduction into long-term transcriptional reprogramming have been well characterized. Chromatin changes have been shown to be involved in photomorphogenesis. However, the initial short-term transcriptional changes produced by light and what factors enable these rapid changes are not well studied. Here, we define rapidly light-responsive, Phytochrome Interacting Factor (PIF) direct-target genes (LRP-DTGs). We found that a majority of these genes also show rapid changes in Histone 3 Lysine-9 acetylation (H3K9ac) in response to the light signal. Detailed time-course analysis of transcript and chromatin changes showed that, for light-repressed genes, H3K9 deacetylation parallels light-triggered transcriptional repression, while for light-induced genes, H3K9 acetylation appeared to somewhat precede light-activated transcript accumulation. However, direct, real-time imaging of transcript elongation in the nucleus revealed that, in fact, transcriptional induction actually parallels H3K9 acetylation. Collectively, the data raise the possibility that light-induced transcriptional and chromatin-remodeling processes are mechanistically intertwined. Histone modifying proteins involved in long term light responses do not seem to have a role in this fast response, indicating that different factors might act at different stages of the light response. This work not only advances our understanding of plant responses to light, but also unveils a system in which rapid chromatin changes in reaction to an external signal can be studied under natural conditions.

Unusual nucleosome formation and transcriptome influence by the histone H3mm18 variant

Histone H3mm18 is a non-allelic H3 variant expressed in skeletal muscle and brain in mice. However, its function has remained enigmatic. We found that H3mm18 is incorporated into chromatin in cells with low efficiency, as compared to H3.3. We determined the structures of the nucleosome core particle (NCP) containing H3mm18 by cryo-electron microscopy, which revealed that the entry/exit DNA regions are drastically disordered in the H3mm18 NCP. Consistently, the H3mm18 NCP is substantially unstable in vitro. The forced expression of H3mm18 in mouse myoblast C2C12 cells markedly suppressed muscle differentiation. A transcriptome analysis revealed that the forced expression of H3mm18 affected the expression of multiple genes, and suppressed a group of genes involved in muscle development. These results suggest a novel gene expression regulation system in which the chromatin landscape is altered by the formation of unusual nucleosomes with a histone variant, H3mm18, and provide important insight into understanding transcription regulation by chromatin.