EED-mediated histone methylation is critical for CNS myelination and remyelination by inhibiting WNT, BMP, and senescence pathways

Targeted disruption of PRC1.1 complex enhances bone remodeling

Polycomb repressive complexes (PRCs) are pivotal epigenetic regulators that preserve cell identity by restricting transcription responses to sub-threshold extracellular signals. Their roles in osteoblast function and bone formation remain unclear. Here in aging osteoblasts, we found marked activation of PRC1.1 complex, with KDM2B acting as a chromatin-binding factor and BCOR and PCGF1 enabling histone H2A monoubiquitylation (H2AK119ub1). Osteoblast-specific Kdm2b inactivation significantly enhances bone remodeling under steady-state conditions and in scenarios of bone loss. This enhancement is attributed to H2AK119ub1 downregulation and subsequent Wnt signaling derepression. Furthermore, we developed a small molecule termed iBP, that specifically inhibits the interaction between BCOR and PCGF1, thereby suppressing PRC1.1 activity. Notably, iBP administration promotes bone formation in mouse models of bone loss. Therefore, our findings identify PRC1.1 as a critical epigenetic brake on bone formation and demonstrate that therapeutic targeting of this complex enhances Wnt pathway activation, offering a promising strategy against skeletal deterioration.

Inhibition of EED-mediated histone methylation alleviates neuroinflammation by suppressing WNT-mediated dendritic cell migration

The epigenetic modification of histone H3 lysine 27 trimethylation (H3K27me3) by the embryonic ectoderm development (EED) protein is closely associated with the regulation of transcriptional programs and is implicated in autoimmune diseases. However, the efficacy of targeting H3K27me3 for the treatment of neuroinflammation remains unclear. In this study, we demonstrate that systemic administration of an EED inhibitor diminishes the inflammatory response mediated by dendritic cells (DCs), thereby alleviating experimental autoimmune encephalitis (EAE), a representative mouse model of autoimmune diseases in the central nervous system (CNS). Our findings indicate that EED inhibitors suppress DC migration by upregulating genes in the WNT signaling pathway that are epigenetically marked by H3K27me3. Conversely, inhibiting the WNT pathway partially reverses the impaired DC migration caused by EED inhibitors. Additionally, the genetic deletion of Eed inhibits DC migration and effectively mitigates autoimmune symptoms and inflammatory infiltration into the CNS in EAE. These results highlight EED as a critical regulator of DC migration and suggest its potential as a therapeutic target for autoimmune disorders.

An oligodendrocyte silencer element underlies the pathogenic impact of lamin B1 structural variants

The role of non-coding regulatory elements and how they might contribute to tissue type specificity of disease phenotypes is poorly understood. Autosomal Dominant Leukodystrophy (ADLD) is a fatal, adult-onset, neurological disorder that is characterized by extensive CNS demyelination. Most cases of ADLD are caused by tandem genomic duplications involving the lamin B1 gene (LMNB1) while a small subset are caused by genomic deletions upstream of the gene. Utilizing data from recently identified families that carry LMNB1 gene duplications but do not exhibit demyelination, ADLD patient tissues, CRISPR edited cell lines and mouse models, we have identified a silencer element that is lost in ADLD patients and that specifically targets expression to oligodendrocytes. This element consists of CTCF binding sites that mediate three-dimensional chromatin looping involving LMNB1 and the recruitment of the PRC2 transcriptional repressor complex. Loss of the silencer element in ADLD identifies a role for non-coding regulatory elements in tissue specificity and disease causation.

An EED/PRC2-H19 Loop Regulates Cerebellar Development

EED (embryonic ectoderm development) is a core subunit of the polycomb repressive complex 2 (PRC2), which senses the trimethylation of histone H3 lysine 27 (H3K27). However, its biological function in cerebellar development remains unknown. Here, we show that EED deletion from neural stem cells (NSCs) or cerebellar granule cell progenitors (GCPs) leads to reduced GCPs proliferation, cell death, cerebellar hypoplasia, and motor deficits in mice. Joint profiling of transcripts and ChIP-seq analysis in cerebellar granule cells reveals that EED regulates bunches of genes involved in cerebellar development. EED ablation exhibits overactivation of a developmental repressor long non-coding RNA H19. Importantly, an obvious H3K27ac enrichment is found at Ctcf, a trans-activator of H19, and H3K27me3 enrichment at the H19 imprinting control region (ICR), suggesting that EED regulates H19 in an H3K27me3-dependent manner. Intriguingly, H19 deletion reduces EED expression and the reprogramming of EED-mediated H3K27me3 profiles, resulting in increased proliferation, differentiation, and decreased apoptosis of GCPs. Finally, molecular and genetic evidence provides that increased H19 expression is responsible for cerebellar hypoplasia and motor defects in EED mutant mice. Thus, this study demonstrates that EED, H19 forms a negative feedback loop, which plays a crucial role in cerebellar morphogenesis and controls cerebellar development.

The role of EZH2 and its regulatory lncRNAs as a serum-based biomarker in Alzheimer's disease

BACKGROUND

Long noncoding RNAs (lncRNAs) have become a hot topic in the human nervous system. Moreover, circulating lncRNAs have been suggested as possible biomarkers for central nervous system processes and neurodegenerative diseases. The present research aimed to highlight the role of plasma lncRNAs TUG1, FEZF1-AS1, and EZH2 gene as diagnostic biomarkers in Alzheimer's disease (AD).

METHODS

Plasma samples for the study were provided by 100 AD patients and 100 matched controls. Real-time quantitative reverse transcriptase PCR was used to determine the plasma level of the aforementioned lncRNAs. Furthermore, the plasma level of EZH2 protein in the participants' blood was determined using the ELISA technique.

RESULTS

In contrast to controls, down-regulation of the EZH2 gene and protein was reported in the plasma of patients with AD. Additionally, plasma samples from AD patients showed up-and-down-regulation of the lncRNAs TUG1 and FEZF1-AS1, respectively.

CONCLUSION

Our new findings suggest that the EZH2 gene, plasma lncRNA TUG1, and FEZF1-AS1 may contribute, as valuable biomarkers, to AD diagnosis.

BRG1 programs PRC2-complex repression and controls oligodendrocyte differentiation and remyelination

Chromatin-remodeling protein BRG1/SMARCA4 is pivotal for establishing oligodendrocyte (OL) lineage identity. However, its functions for oligodendrocyte-precursor cell (OPC) differentiation within the postnatal brain and during remyelination remain elusive. Here, we demonstrate that Brg1 loss profoundly impairs OPC differentiation in the brain with a comparatively lesser effect in the spinal cord. Moreover, BRG1 is critical for OPC remyelination after injury. Integrative transcriptomic/genomic profiling reveals that BRG1 exhibits a dual role by promoting OPC differentiation networks while repressing OL-inhibitory cues and proneuronal programs. Furthermore, we find that BRG1 interacts with EED/PRC2 polycomb-repressive-complexes to enhance H3K27me3-mediated repression at gene loci associated with OL-differentiation inhibition and neurogenesis. Notably, BRG1 depletion decreases H3K27me3 deposition, leading to the upregulation of BMP/WNT signaling and proneurogenic genes, which suppresses OL programs. Thus, our findings reveal a hitherto unexplored spatiotemporal-specific role of BRG1 for OPC differentiation in the developing CNS and underscore a new insight into BRG1/PRC2-mediated epigenetic regulation that promotes and safeguards OL lineage commitment and differentiation.

Regulators of Oligodendrocyte Differentiation

Myelination has evolved as a mechanism to ensure fast and efficient propagation of nerve impulses along axons. Within the central nervous system (CNS), myelination is carried out by highly specialized glial cells, oligodendrocytes. The formation of myelin is a prolonged aspect of CNS development that occurs well into adulthood in humans, continuing throughout life in response to injury or as a component of neuroplasticity. The timing of myelination is tightly tied to the generation of oligodendrocytes through the differentiation of their committed progenitors, oligodendrocyte precursor cells (OPCs), which reside throughout the developing and adult CNS. In this article, we summarize our current understanding of some of the signals and pathways that regulate the differentiation of OPCs, and thus the myelination of CNS axons.

BMP-ACVR1 Axis is Critical for Efficacy of PRC2 Inhibitors in B-Cell Lymphoma

EZH2 is the catalytic subunit of the histone methyltransferase Polycomb Repressive Complex 2 (PRC2), and its somatic activating mutations drive lymphoma, particularly the germinal center B-cell type. Although PRC2 inhibitors, such as tazemetostat, have demonstrated anti-lymphoma activity in patients, the clinical efficacy is not limited to EZH2-mutant lymphoma. In this study, Activin A Receptor Type 1 (ACVR1), a type I Bone Morphogenetic Protein (BMP) receptor, is identified as critical for the anti-lymphoma efficacy of PRC2 inhibitors through a whole-genome CRISPR screen. BMP6, BMP7, and ACVR1 are repressed by PRC2-mediated H3K27me3, and PRC2 inhibition upregulates their expression and signaling in cell and patient-derived xenograft models. Through BMP-ACVR1 signaling, PRC2 inhibitors robustly induced cell cycle arrest and B cell lineage differentiation in vivo. Remarkably, blocking ACVR1 signaling using an inhibitor or genetic depletion significantly compromised the in vitro and in vivo efficacy of PRC2 inhibitors. Furthermore, high levels of BMP6 and BMP7, along with ACVR1, are associated with longer survival in lymphoma patients, underscoring the clinical relevance of this study. Altogether, BMP-ACVR1 exhibits anti-lymphoma function and represents a critical PRC2-repressed pathway contributing to the efficacy of PRC2 inhibitors.

HMGA1 drives chemoresistance in esophageal squamous cell carcinoma by suppressing ferroptosis

Chemotherapy is a primary treatment for esophageal squamous cell carcinoma (ESCC). Resistance to chemotherapeutic drugs is an important hurdle to effective treatment. Understanding the mechanisms underlying chemotherapy resistance in ESCC is an unmet medical need to improve the survival of ESCC. Herein, we demonstrate that ferroptosis triggered by inhibiting high mobility group AT-hook 1 (HMGA1) may provide a novel opportunity to gain an effective therapeutic strategy against chemoresistance in ESCC. HMGA1 is upregulated in ESCC and works as a key driver for cisplatin (DDP) resistance in ESCC by repressing ferroptosis. Inhibition of HMGA1 enhances the sensitivity of ESCC to ferroptosis. With a transcriptome analysis and following-up assays, we demonstrated that HMGA1 upregulates the expression of solute carrier family 7 member 11 (SLC7A11), a key transporter maintaining intracellular glutathione homeostasis and inhibiting the accumulation of malondialdehyde (MDA), thereby suppressing cell ferroptosis. HMGA1 acts as a chromatin remodeling factor promoting the binding of activating transcription factor 4 (ATF4) to the promoter of SLC7A11, and hence enhancing the transcription of SLC7A11 and maintaining the redox balance. We characterized that the enhanced chemosensitivity of ESCC is primarily attributed to the increased susceptibility of ferroptosis resulting from the depletion of HMGA1. Moreover, we utilized syngeneic allograft tumor models and genetically engineered mice of HMGA1 to induce ESCC and validated that depletion of HMGA1 promotes ferroptosis and restores the sensitivity of ESCC to DDP, and hence enhances the therapeutic efficacy. Our finding uncovers a critical role of HMGA1 in the repression of ferroptosis and thus in the establishment of DDP resistance in ESCC, highlighting HMGA1-based rewiring strategies as potential approaches to overcome ESCC chemotherapy resistance. Schematic depicting that HMGA1 maintains intracellular redox homeostasis against ferroptosis by assisting ATF4 to activate SLC7A11 transcription, resulting in ESCC resistance to chemotherapy.

KDM2B regulates hippocampal morphogenesis by transcriptionally silencing Wnt signaling in neural progenitors

The hippocampus plays major roles in learning and memory, and its formation requires precise coordination of patterning, cell proliferation, differentiation, and migration. Here we removed the chromatin-association capability of KDM2B in the progenitors of developing dorsal telencephalon (Kdm2b∆CxxC) to discover that Kdm2b∆CxxC hippocampus, particularly the dentate gyrus, became drastically smaller with disorganized cellular components and structure. Kdm2b∆CxxC mice display prominent defects in spatial memory, motor learning and fear conditioning, resembling patients with KDM2B mutations. The migration and differentiation of neural progenitor cells is greatly impeded in the developing Kdm2b∆CxxC hippocampus. Mechanism studies reveal that Wnt signaling genes in developing Kdm2b∆CxxC hippocampi are de-repressed due to reduced enrichment of repressive histone marks by polycomb repressive complexes. Activating the Wnt signaling disturbs hippocampal neurogenesis, recapitulating the effect of KDM2B loss. Together, we unveil a previously unappreciated gene repressive program mediated by KDM2B that controls progressive fate specifications and cell migration, hence morphogenesis of the hippocampus.

Relating enhancer genetic variation across mammals to complex phenotypes using machine learning

Protein-coding differences between species often fail to explain phenotypic diversity, suggesting the involvement of genomic elements that regulate gene expression such as enhancers. Identifying associations between enhancers and phenotypes is challenging because enhancer activity can be tissue-dependent and functionally conserved despite low sequence conservation. We developed the Tissue-Aware Conservation Inference Toolkit (TACIT) to associate candidate enhancers with species' phenotypes using predictions from machine learning models trained on specific tissues. Applying TACIT to associate motor cortex and parvalbumin-positive interneuron enhancers with neurological phenotypes revealed dozens of enhancer-phenotype associations, including brain size-associated enhancers that interact with genes implicated in microcephaly or macrocephaly. TACIT provides a foundation for identifying enhancers associated with the evolution of any convergently evolved phenotype in any large group of species with aligned genomes.

The epigenetic landscape of oligodendrocyte lineage cells

The epigenetic landscape of oligodendrocyte lineage cells refers to the cell-specific modifications of DNA, chromatin, and RNA that define a unique gene expression pattern of functionally specialized cells. Here, we focus on the epigenetic changes occurring as progenitors differentiate into myelin-forming cells and respond to the local environment. First, modifications of DNA, RNA, nucleosomal histones, key principles of chromatin organization, topologically associating domains, and local remodeling will be reviewed. Then, the relationship between epigenetic modulators and RNA processing will be explored. Finally, the reciprocal relationship between the epigenome as a determinant of the mechanical properties of cell nuclei and the target of mechanotransduction will be discussed. The overall goal is to provide an interpretative key on how epigenetic changes may account for the heterogeneity of the transcriptional profiles identified in this lineage.

Epigenetic regulation of embryonic ectoderm development in stem cell differentiation and transformation during ontogenesis

Dynamic chromatin accessibility regulates stem cell fate determination and tissue homeostasis via controlling gene expression. As a histone-modifying enzyme that predominantly mediates methylation of lysine 27 in histone H3 (H3K27me1/2/3), Polycomb repressive complex 2 (PRC2) plays the canonical role in targeting developmental regulators during stem cell differentiation and transformation. Embryonic ectoderm development (EED), the core scaffold subunit of PRC2 and as an H3K27me3-recognizing protein, has been broadly implicated with PRC2 stabilization and allosterically stimulated PRC2. Accumulating evidences from experimental data indicate that EED-associating epigenetic modifications are indispensable for stem cell maintenance and differentiation into specific cell lineages. In this review, we discuss the most updated advances to summarize the structural architecture of EED and its contributions and underlying mechanisms to mediating lineage differentiation of different stem cells during epigenetic modification to expand our understanding of PRC2.

Abnormal neural differentiation in response to graphene quantum dots through histone modification interference

Graphene quantum dots (GQDs) have been broadly applied in biomedicine in recent years, and their environmental exposure and toxicological impacts have raised increasing concerns. The nanosafety assessment on the nervous system is one of the most important aspects, and potential effects of GQDs on neurodevelopment and the underlying mechanism are still elusive. In this study, the neural developmental toxicities of OH-GQDs and NH₂-GQDs were investigated using the mouse embryonic stem cells (mESCs). The results revealed that OH-GQDs significantly inhibited the ectoderm development, and reduced the neural precursor formation and neurogenesis during the neural differentiation of the mESCs. The exploration on the mechanism uncovered that the increased enrichment of H3K27me3 at the promoter region of the Smad6 gene was involved in histone modification-activated BMP signal pathway, which consequently influenced its regulatory effects on neural differentiation. Additionally, OH-GQDs elicited a stronger effect on inducing the imbalance of histone modification, and resulted in higher latency of neural differentiation disturbance than did NH₂-GQDs, suggesting surface functionalization-specific effects of GQDs on neurodevelopmental toxicity. This study would provide new insights in not only the adverse effects of GQDs on neurodevelopment, but also the influence from the chemical modification of GQDs on their bioactivities.

Olig2 Ablation in Immature Oligodendrocytes Does Not Enhance CNS Myelination and Remyelination

The oligodendrocyte (OL) lineage transcription factor Olig2 is expressed throughout oligodendroglial development and is essential for oligodendroglial progenitor specification and differentiation. It was previously reported that deletion of Olig2 enhanced the maturation and myelination of immature OLs and accelerated the remyelination process. However, by analyzing multiple Olig2 conditional KO mouse lines (male and female), we conclude that Olig2 has the opposite effect and is required for OL maturation and remyelination. We found that deletion of Olig2 in immature OLs driven by an immature OL-expressing Plp1 promoter resulted in defects in OL maturation and myelination, and did not enhance remyelination after demyelination. Similarly, Olig2 deletion during premyelinating stages in immature OLs using Mobp or Mog promoter-driven Cre lines also did not enhance OL maturation in the CNS. Further, we found that Olig2 was not required for myelin maintenance in mature OLs but was critical for remyelination after lysolecithin-induced demyelinating injury. Analysis of genomic occupancy in immature and mature OLs revealed that Olig2 targets the enhancers of key myelination-related genes for OL maturation from immature OLs. Together, by leveraging multiple immature OL-expressing Cre lines, these studies indicate that Olig2 is essential for differentiation and myelination of immature OLs and myelin repair. Our findings raise fundamental questions about the previously proposed role of Olig2 in opposing OL myelination and highlight the importance of using Cre-dependent reporter(s) for lineage tracing in studying cell state progression.SIGNIFICANCE STATEMENT Identification of the regulators that promote oligodendrocyte (OL) myelination and remyelination is important for promoting myelin repair in devastating demyelinating diseases. Olig2 is expressed throughout OL lineage development. Ablation of Olig2 was reported to induce maturation, myelination, and remyelination from immature OLs. However, lineage-mapping analysis of Olig2-ablated cells was not conducted. Here, by leveraging multiple immature OL-expressing Cre lines, we observed no evidence that Olig2 ablation promotes maturation or remyelination of immature OLs. Instead, we find that Olig2 is required for immature OL maturation, myelination, and myelin repair. These data raise fundamental questions about the proposed inhibitory role of Olig2 against OL maturation and remyelination. Our findings highlight the importance of validating genetic manipulation with cell lineage tracing in studying myelination.

Tissue-wide genetic and cellular landscape shapes the execution of sequential PRC2 functions in neural stem cell lineage progression

The generation of a correctly sized cerebral cortex with all-embracing neuronal and glial cell-type diversity critically depends on faithful radial glial progenitor (RGP) cell proliferation/differentiation programs. Temporal RGP lineage progression is regulated by Polycomb repressive complex 2 (PRC2), and loss of PRC2 activity results in severe neurogenesis defects and microcephaly. How PRC2-dependent gene expression instructs RGP lineage progression is unknown. Here, we use mosaic analysis with double markers (MADM)-based single-cell technology and demonstrate that PRC2 is not cell-autonomously required in neurogenic RGPs but rather acts at the global tissue-wide level. Conversely, cortical astrocyte production and maturation is cell-autonomously controlled by PRC2-dependent transcriptional regulation. We thus reveal highly distinct and sequential PRC2 functions in RGP lineage progression that are dependent on complex interplays between intrinsic and tissue-wide properties. In a broader context, our results imply a critical role for the genetic and cellular niche environment in neural stem cell behavior.

Loss of microglial EED impairs synapse density, learning, and memory

The embryonic ectoderm development (EED) is a core component of the polycomb-repressive complex 2 (PRC2) whose mutations are linked to neurodevelopmental abnormalities, intellectual disability, and neurodegeneration. Although EED has been extensively studied in neural stem cells and oligodendrocytes, its role in microglia is incompletely understood. Here, we show that microglial EED is essential for synaptic pruning during the postnatal stage of brain development. The absence of microglial EED at early postnatal stages resulted in reduced spines and impaired synapse density in the hippocampus at adulthood, accompanied by upregulated expression of phagocytosis-related genes in microglia. As a result, deletion of microglial Eed impaired hippocampus-dependent learning and memory in mice. These results suggest that microglial EED is critical for normal synaptic and cognitive functions during postnatal development.

Histone Lysine Methylation Modification and Its Role in Vascular Calcification

Histone methylation is an epigenetic change mediated by histone methyltransferase, and has been connected to the beginning and progression of several diseases. The most common ailments that affect the elderly are cardiovascular and cerebrovascular disorders. They are the leading causes of death, and their incidence is linked to vascular calcification (VC). The key mechanism of VC is the transformation of vascular smooth muscle cells (VSMCs) into osteoblast-like phenotypes, which is a highly adjustable process involving a variety of complex pathophysiological processes, such as metabolic abnormalities, apoptosis, oxidative stress and signalling pathways. Many researchers have investigated the mechanism of VC and related targets for the prevention and treatment of cardiovascular and cerebrovascular diseases. Their findings revealed that histone lysine methylation modification may play a key role in the various stages of VC. As a result, a thorough examination of the role and mechanism of lysine methylation modification in physiological and pathological states is critical, not only for identifying specific molecular markers of VC and new therapeutic targets, but also for directing the development of new related drugs. Finally, we provide this review to discover the association between histone methylation modification and VC, as well as diverse approaches with which to investigate the pathophysiology of VC and prospective treatment possibilities.

The Oligodendrocyte Transcription Factor 2 OLIG2 regulates transcriptional repression during myelinogenesis in rodents

OLIG2 is a transcription factor that activates the expression of myelin-associated genes in the oligodendrocyte-lineage cells. However, the mechanisms of myelin gene inactivation are unclear. Here, we uncover a non-canonical function of OLIG2 in transcriptional repression to modulate myelinogenesis by functionally interacting with tri-methyltransferase SETDB1. Immunoprecipitation and chromatin-immunoprecipitation assays show that OLIG2 recruits SETDB1 for H3K9me3 modification on the Sox11 gene, which leads to the inhibition of Sox11 expression during the differentiation of oligodendrocytes progenitor cells (OPCs) into immature oligodendrocytes (iOLs). Tissue-specific depletion of Setdb1 in mice results in the hypomyelination during development and remyelination defects in the injured rodents. Knockdown of Sox11 by siRNA in rat primary OPCs or depletion of Sox11 in the oligodendrocyte lineage in mice could rescue the hypomyelination phenotype caused by the loss of OLIG2. In summary, our work demonstrates that the OLIG2-SETDB1 complex can mediate transcriptional repression in OPCs, affecting myelination.

Transcription factors regulate gene programs during myelination. Here, the authors show that the Oligodendrocyte Transcription Factor 2 (OLIG2) regulates the differentiation of oligodendrocyte progenitor cells into immature oligodendrocytes via SETDB1 during myelination and remyelination in rodents.

New Insights of CCR7 Signaling in Dendritic Cell Migration and Inflammatory Diseases

CCR7, collaborated with its ligands CCL19 and CCL21, controls extensive migratory events in the immune system. CCR7-bearing dendritic cells can swarm into T-cell zones in lymph nodes, initiating the antigen presentation and T-cell response. Abnormal expression of CCR7 in dendritic cells will cause a series of inflammatory diseases due to the chaotic dendritic cell trafficking. In this review, we take an in-depth look at the structural–functional domains of CCR7 and CCR7-bearing dendritic cell trajectory to lymph nodes. Then, we summarize the regulatory network of CCR7, including transcriptional regulation, translational and posttranslational regulation, internalization, desensitization, and recycling. Furthermore, the potential strategies of targeting the CCR7 network to regulate dendritic cell migration and to deal with inflammatory diseases are integrated, which not only emphasizes the possibility of CCR7 to be a potential target of immunotherapy but also has an implication on the homing of dendritic cells to benefit inflammatory diseases.

Reprogramming of the epigenome in neurodevelopmental disorders

The etiology of neurodevelopmental disorders (NDDs) remains a challenge for researchers. Human brain development is tightly regulated and sensitive to cellular alterations caused by endogenous or exogenous factors. Intriguingly, the surge of clinical sequencing studies has revealed that many of these disorders are monogenic and monoallelic. Notably, chromatin regulation has emerged as highly dysregulated in NDDs, with many syndromes demonstrating phenotypic overlap, such as intellectual disabilities, with one another. Here we discuss epigenetic writers, erasers, readers, remodelers, and even histones mutated in NDD patients, predicted to affect gene regulation. Moreover, this review focuses on disorders associated with mutations in enzymes involved in histone acetylation and methylation, and it highlights syndromes involving chromatin remodeling complexes. Finally, we explore recently discovered histone germline mutations and their pathogenic outcome on neurological function. Epigenetic regulators are mutated at every level of chromatin organization. Throughout this review, we discuss mechanistic investigations, as well as various animal and iPSC models of these disorders and their usefulness in determining pathomechanism and potential therapeutics. Understanding the mechanism of these mutations will illuminate common pathways between disorders. Ultimately, classifying these disorders based on their effects on the epigenome will not only aid in prognosis in patients but will aid in understanding the role of epigenetic machinery throughout neurodevelopment.

Osteocalcin attenuates oligodendrocyte differentiation and myelination via GPR37 signaling in the mouse brain

The bone-derived hormone osteocalcin (OCN) is crucial for brain development and neural cognitive functions, yet the exact roles of OCN in central nervous system (CNS) remain elusive. Here, we find that genetic deletion of OCN facilitates oligodendrocyte (OL) differentiation and hypermyelination in the CNS. Although dispensable for the proliferation of oligodendrocyte precursor cells (OPCs), OCN is critical for the myelination of OLs, which affects myelin production and remyelination after demyelinating injury. Genome-wide RNA sequencing analyses reveal that OCN regulates a number of G protein–coupled receptors and myelination-associated transcription factors, of which Myrf might be a key downstream effector in OLs. GPR37 is identified as a previously unknown receptor for OCN, thus regulating OL differentiation and CNS myelination. Overall, these findings suggest that OCN orchestrates the transition between OPCs and myelinating OLs via GPR37 signaling, and hence, the OCN/GPR37 pathway regulates myelin homeostasis in the CNS.

Histone H3K27 methylation-mediated repression of Hairy regulates insect developmental transition by modulating ecdysone biosynthesis

Insect development is cooperatively orchestrated by the steroid hormone ecdysone and juvenile hormone (JH). The polycomb repressive complex 2 (PRC2)-mediated histone H3K27 trimethylation (H3K27me3) epigenetically silences gene transcription and is essential for a range of biological processes, but the functions of H3K27 methylation in insect hormone action are poorly understood. Here, we demonstrate that H3K27 methylation-mediated repression of Hairy transcription in the larval prothoracic gland (PG) is required for ecdysone biosynthesis in Bombyx and Drosophila H3K27me3 levels in the PG are dynamically increased during the last larval instar. H3K27me3 reduction induced by the down-regulation of PRC2 activity via inhibitor treatment in Bombyx or PG-specific knockdown of the PRC2 component Su(z)12 in Drosophila diminishes ecdysone biosynthesis and disturbs the larval-pupal transition. Mechanistically, H3K27 methylation targets the JH signal transducer Hairy to repress its transcription in the PG; PG-specific knockdown or overexpression of the Hairy gene disrupts ecdysone biosynthesis and developmental transition; and developmental defects caused by PG-specific Su(z)12 knockdown can be partially rescued by Hairy down-regulation. The application of JH mimic to the PG decreases both H3K27me3 levels and Su(z)12 expression. Altogether, our study reveals that PRC2-mediated H3K27 methylation at Hairy in the PG during the larval period is required for ecdysone biosynthesis and the larval-pupal transition and provides insights into epigenetic regulation of the crosstalk between JH and ecdysone during insect development.

Oligodendroglial ring finger protein Rnf43 is an essential injury-specific regulator of oligodendrocyte maturation

Oligodendrocyte (OL) maturation arrest in human white matter injury contributes significantly to the failure of endogenous remyelination in multiple sclerosis (MS) and newborn brain injuries such as hypoxic ischemic encephalopathy (HIE) that cause cerebral palsy. In this study, we identify an oligodendroglial-intrinsic factor that controls OL maturation specifically in the setting of injury. We find a requirement for the ring finger protein Rnf43 not in normal development but in neonatal hypoxic injury and remyelination in the adult mammalian CNS. Rnf43, but not the related Znrf3, is potently activated by Wnt signaling in OL progenitor cells (OPCs) and marks activated OPCs in human MS and HIE. Rnf43 is required in an injury-specific context, and it promotes OPC differentiation through negative regulation of Wnt signal strength in OPCs at the level of Fzd1 receptor presentation on the cell surface. Inhibition of Fzd1 using UM206 promotes remyelination following ex vivo and in vivo demyelinating injury.

Single-cell CUT&Tag profiles histone modifications and transcription factors in complex tissues

In contrast to single-cell approaches for measuring gene expression and DNA accessibility, single-cell methods for analyzing histone modifications are limited by low sensitivity and throughput. Here, we combine the CUT&Tag technology, developed to measure bulk histone modifications, with droplet-based single-cell library preparation to produce high-quality single-cell data on chromatin modifications. We apply single-cell CUT&Tag (scCUT&Tag) to tens of thousands of cells of the mouse central nervous system and probe histone modifications characteristic of active promoters, enhancers and gene bodies (H3K4me3, H3K27ac and H3K36me3) and inactive regions (H3K27me3). These scCUT&Tag profiles were sufficient to determine cell identity and deconvolute regulatory principles such as promoter bivalency, spreading of H3K4me3 and promoter-enhancer connectivity. We also used scCUT&Tag to investigate the single-cell chromatin occupancy of transcription factor OLIG2 and the cohesin complex component RAD21. Our results indicate that analysis of histone modifications and transcription factor occupancy at single-cell resolution provides unique insights into epigenomic landscapes in the central nervous system.

Histopathological and epigenetic alterations in the spinal cord due to prenatal electromagnetic field exposure: An H3K27me3-related mechanism

Neural system development is one of the most important stages of embryogenesis. Perturbations in this crucial process due to genetic and environmental risk factors cause neural tube defects and other central nervous system diseases. We investigated the effects of prenatal exposure to 900-MHz electromagnetic field (EMF) on the spinal cord. Pregnant rats were exposed to 900-MHz EMF for 1 h/day from E13.5 until birth. Six pups from the control and EMF groups were sacrificed at postnatal day 32, and the upper thoracic region of the spine was removed and processed for histological procedures. For histopathological analyses, hematoxylin&eosin staining and, for stereological analyses and the quantitation of motor neurons, cresyl violet staining was performed. H3K27me3 levels were determined via immunofluorescence staining. Histopathological analysis identified structural alterations of ependymal cells, enlarged central canals, as well as degenerated and shrunken motor neurons in the EMF group, while the control group tissues had normal appearances. We also observed enrichment of H3K27me3 in the ependymal cells and the motor neurons in the spinal cord of the control group rats, while the EMF group had low levels of H3K27me3 staining. Our results suggest that the loss of H3K27me3 signals might correlate with reduced neuronal stem cell potential in the EMF group and result in anatomical and structural differences in the spinal cord. This study provided a comprehensive histopathological analysis of the spinal cord after prenatal EMF exposure and offered an H3K27me3-dependent molecular explanation for the detrimental effects of EMF exposure on the spine.

Oligodendroglial Epigenetics, from Lineage Specification to Activity-Dependent Myelination

Oligodendroglial cells are the myelinating cells of the central nervous system. While myelination is crucial to axonal activity and conduction, oligodendrocyte progenitor cells and oligodendrocytes have also been shown to be essential for neuronal support and metabolism. Thus, a tight regulation of oligodendroglial cell specification, proliferation, and myelination is required for correct neuronal connectivity and function. Here, we review the role of epigenetic modifications in oligodendroglial lineage cells. First, we briefly describe the epigenetic modalities of gene regulation, which are known to have a role in oligodendroglial cells. We then address how epigenetic enzymes and/or marks have been associated with oligodendrocyte progenitor specification, survival and proliferation, differentiation, and finally, myelination. We finally mention how environmental cues, in particular, neuronal signals, are translated into epigenetic modifications, which can directly influence oligodendroglial biology.

Convergent epigenetic regulation of glial plasticity in myelin repair and brain tumorigenesis: A focus on histone modifying enzymes

Brain regeneration and tumorigenesis are complex processes involving in changes in chromatin structure to regulate cellular states at the molecular and genomic level. The modulation of chromatin structure dynamics is critical for maintaining progenitor cell plasticity, growth and differentiation. Oligodendrocyte precursor cells (OPC) can be differentiated into mature oligodendrocytes, which produce myelin sheathes to permit saltatory nerve conduction. OPCs and their primitive progenitors such as pri-OPC or pre-OPC are highly adaptive and plastic during injury repair or brain tumor formation. Recent studies indicate that chromatin modifications and epigenetic homeostasis through histone modifying enzymes shape genomic regulatory landscape conducive to OPC fate specification, lineage differentiation, maintenance of myelin sheaths, as well as brain tumorigenesis. Thus, histone modifications can be convergent mechanisms in regulating OPC plasticity and malignant transformation. In this review, we will focus on the impact of histone modifying enzymes in modulating OPC plasticity during normal development, myelin regeneration and tumorigenesis.