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Joint profiling of chromatin accessibility and gene expression in individual cells provides an opportunity to decipher enhancer-driven gene regulatory networks (GRNs). Here we present a method for the inference of enhancer-driven GRNs, called SCENIC+. SCENIC+ predicts genomic enhancers along with candidate upstream transcription factors (TFs) and links these enhancers to candidate target genes. To improve both recall and precision of TF identification, we curated and clustered a motif collection with more than 30,000 motifs. We benchmarked SCENIC+ on diverse datasets from different species, including human peripheral blood mononuclear cells, ENCODE cell lines, melanoma cell states and Drosophila retinal development. Next, we exploit SCENIC+ predictions to study conserved TFs, enhancers and GRNs between human and mouse cell types in the cerebral cortex. Finally, we use SCENIC+ to study the dynamics of gene regulation along differentiation trajectories and the effect of TF perturbations on cell state. SCENIC+ is available at scenicplus.readthedocs.io . SCENIC+ is a comprehensive toolbox for inferring and analyzing enhancer-driven gene regulatory networks using single-cell multiomic data.

Physical access to DNA is a highly dynamic property of chromatin that plays an essential role in establishing and maintaining cellular identity. The organization of accessible chromatin across the genome reflects a network of permissible physical interactions through which enhancers, promoters, insulators and chromatin-binding factors cooperatively regulate gene expression. This landscape of accessibility changes dynamically in response to both external stimuli and developmental cues, and emerging evidence suggests that homeostatic maintenance of accessibility is itself dynamically regulated through a competitive interplay between chromatin-binding factors and nucleosomes. In this Review, we examine how the accessible genome is measured and explore the role of transcription factors in initiating accessibility remodelling; our goal is to illustrate how chromatin accessibility defines regulatory elements within the genome and how these epigenetic features are dynamically established to control gene expression.Chromatin accessibility comprises the positions, compaction and dynamics of nucleosomes, as well as the occupancy of DNA by other proteins such as transcription factors. In this Review, the authors discuss diverse methods for characterizing chromatin accessibility, how accessibility is determined and remodelled in cells and the regulatory roles of accessibility in gene expression and development.

Key Points Active DNA demethylation in mammals is achieved through TET-mediated oxidation of 5-methylcytosine (5mC) to 5-hydroxymethylcytosine (5hmC), 5-formylcytosine (5fC) and 5-carboxylcytosine (5caC), followed by replication-dependent dilution of oxidized 5mC or thymine DNA glycosylase (TDG)-mediated excision of 5fC and 5caC coupled with base excision repair. Active DNA demethylation is regulated at various levels, including substrate and cofactor availability, post-transcriptional and post-translational regulation of TET and TDG, and genomic localization of the demethylation machinery. Studies of tissue distribution, genomic distribution and the dynamics of oxidized 5mC provide insights into the mechanism and function of active DNA demethylation as well as the potential roles of oxidized 5mC. Active DNA demethylation and oxidized 5mC are involved in pre-implantation embryo development, primordial germ cell development, pluripotency and differentiation, as well as neuronal functions. In certain biological contexts, such as in pre-implantation embryos, the biological meaning of TET-mediated oxidation is not fully understood. In some other biological contexts, such as neurons, the extent of active DNA demethylation and its function require further study. TET may function in a catalytic-activity-independent manner. Further analysis is needed to distinguish the functions of the TET proteins themselves from the function of active DNA demethylation. Emerging evidence suggests an interplay between TET, active DNA demethylation and genomic instability and the DNA damage response. A key mode of regulating DNA methylation is through active demethylation driven by TET-mediated oxidation of 5-methylcytosine (5mC). This Review discusses our latest understanding of the mechanisms and regulation of active DNA demethylation, and the roles of active demethylation (and the oxidized 5mC intermediates) in gene regulation, genome stability, development and disease. In mammals, DNA methylation in the form of 5-methylcytosine (5mC) can be actively reversed to unmodified cytosine (C) through TET dioxygenase-mediated oxidation of 5mC to 5-hydroxymethylcytosine (5hmC), 5-formylcytosine (5fC) and 5-carboxylcytosine (5caC), followed by replication-dependent dilution or thymine DNA glycosylase (TDG)-dependent base excision repair. In the past few years, biochemical and structural studies have revealed mechanistic insights into how TET and TDG mediate active DNA demethylation. Additionally, many regulatory mechanisms of this process have been identified. Technological advances in mapping and tracing the oxidized forms of 5mC allow further dissection of their functions. Furthermore, the biological functions of active DNA demethylation in various biological contexts have also been revealed. In this Review, we summarize the recent advances and highlight key unanswered questions.

The gene-regulatory landscape of the brain is highly dynamic in health and disease, coordinating a menagerie of biological processes across distinct cell types. Here, we present a multi-omic single-nucleus study of 191,890 nuclei in late-stage Alzheimer’s disease (AD), accessible through our web portal, profiling chromatin accessibility and gene expression in the same biological samples and uncovering vast cellular heterogeneity. We identified cell-type-specific, disease-associated candidate cis -regulatory elements and their candidate target genes, including an oligodendrocyte-associated regulatory module containing links to APOE and CLU . We describe cis -regulatory relationships in specific cell types at a subset of AD risk loci defined by genome-wide association studies, demonstrating the utility of this multi-omic single-nucleus approach. Trajectory analysis of glial populations identified disease-relevant transcription factors, such as SREBF1, and their regulatory targets. Finally, we introduce single-nucleus consensus weighted gene coexpression analysis, a coexpression network analysis strategy robust to sparse single-cell data, and perform a systems-level analysis of the AD transcriptome. An integrative analysis of single-nucleus assay for transposase-accessible chromatin with sequencing and RNA sequencing in normal and Alzheimer’s disease brain tissue identifies cell-type-specific cis -regulatory elements and candidate target genes at disease-associated loci.

Key Points The functional classification system introduced here divides the genes that shape the cancer epigenome into three categories: epigenetic modifiers that directly modify the cancer epigenome and are frequent targets of mutations and epimutations; epigenetic mediators that drive the tumour or its progenitor cells towards a more stem-like state; and epigenetic modulators that transmit environmental signals to epigenetic modifiers. Epigenetic mediator-induced epigenetic variation in the cells of origin might lead to increased phenotypic flexibility and heterogeneity long before the emergence of oncogenic mutations and is subsequently selected in the tumour tissue during progression. Sites of increased epigenetic variation in precancerous lesions and cancer localize to large domains, called hypomethylated blocks, that overlap with regions of repressive chromatin modifications acquired during development (large organized chromatin K9 modifications) and are particularly sensitive to ageing and cancer-predisposing environmental signals. Increased epigenetic variation is a predictor of cancer risk and cancer progression; it promotes the adaptation of the tumour tissue to changing environmental cues by continuously re-establishing tumour cell phenotypic heterogeneity. The mechanism of increased epigenetic variation is functionally intertwined with the perturbations of the 3D genome organization and the disruption of heterochromatin compartments within the nuclear architecture. Disruption to the epigenome is increasingly appreciated as a major contributor to the development of cancer. The authors discuss how conceptualizing genes affecting the epigenome as epigenetic modulators, epigenetic modifiers or epigenetic mediators provides a valuable framework for understanding diverse aspects of the causes and consequences of epigenome alteration in cancer. This year is the tenth anniversary of the publication in this journal of a model suggesting the existence of 'tumour progenitor genes'. These genes are epigenetically disrupted at the earliest stages of malignancies, even before mutations, and thus cause altered differentiation throughout tumour evolution. The past decade of discovery in cancer epigenetics has revealed a number of similarities between cancer genes and stem cell reprogramming genes, widespread mutations in epigenetic regulators, and the part played by chromatin structure in cellular plasticity in both development and cancer. In the light of these discoveries, we suggest here a framework for cancer epigenetics involving three types of genes: 'epigenetic mediators', corresponding to the tumour progenitor genes suggested earlier; 'epigenetic modifiers' of the mediators, which are frequently mutated in cancer; and 'epigenetic modulators' upstream of the modifiers, which are responsive to changes in the cellular environment and often linked to the nuclear architecture. We suggest that this classification is helpful in framing new diagnostic and therapeutic approaches to cancer.

The overwhelming majority of participants in current genetic studies are of European ancestry. To elucidate disease biology in the East Asian population, we conducted a genome-wide association study (GWAS) with 212,453 Japanese individuals across 42 diseases. We detected 320 independent signals in 276 loci for 27 diseases, with 25 novel loci ( P  < 9.58 × 10 −9 ). East Asian–specific missense variants were identified as candidate causal variants for three novel loci, and we successfully replicated two of them by analyzing independent Japanese cohorts; p.R220W of ATG16L2 (associated with coronary artery disease) and p.V326A of POT1 (associated with lung cancer). We further investigated enrichment of heritability within 2,868 annotations of genome-wide transcription factor occupancy, and identified 378 significant enrichments across nine diseases (false discovery rate < 0.05) (for example, NKX3-1 for prostate cancer). This large-scale GWAS in a Japanese population provides insights into the etiology of complex diseases and highlights the importance of performing GWAS in non-European populations. Genome-wide analysis in 212,453 Japanese individuals identifies loci associated with 42 diseases. Comparative analysis with European populations identifies East Asian–specific associations.

Maintenance of genome stability requires control over the expression of transposable elements (TEs), whose activity can have substantial deleterious effects on the host. Chemical modification of DNA is a commonly used strategy to achieve this, and it has long been argued that the emergence of 5-methylcytosine (5mC) in many species was driven by the requirement to silence TEs. Potential roles in TE regulation have also been suggested for other DNA modifications, such as N6-methyladenine and oxidation derivatives of 5mC, although the underlying mechanistic relationships are poorly understood. Here, we discuss current evidence implicating DNA modifications and DNA-modifying enzymes in TE regulation across different species.Transposable elements (TEs) need to be tightly regulated in genomes to prevent the detrimental consequences of transposition. In this Review, Deniz, Frost and Branco discuss how DNA methylation dynamics play a central role in the multilayered epigenetic mechanisms regulating TEs. Beyond roles for 5-methylcytosine (5mC), they discuss TET-mediated oxidation products of 5mC, as well as ongoing debates about the functional relevance of adenine methylation.

Annotating the molecular basis of human disease remains an unsolved challenge, as 93% of disease loci are non-coding and gene-regulatory annotations are highly incomplete 1 , 2 – 3 . Here we present EpiMap, a compendium comprising 10,000 epigenomic maps across 800 samples, which we used to define chromatin states, high-resolution enhancers, enhancer modules, upstream regulators and downstream target genes. We used this resource to annotate 20,000 genetic loci that were associated with 232 traits 4 , predicting trait-relevant tissues, putative causal nucleotide variants in enriched tissue enhancers and candidate tissue-specific target genes for each. We partitioned multifactorial traits into tissue-specific contributing factors with distinct functional enrichments and disease comorbidity patterns, and revealed both single-factor monotropic and multifactor pleiotropic loci. Top-scoring loci frequently had multiple predicted driver variants, converging through multiple enhancers with a common target gene, multiple genes in common tissues, or multiple genes and multiple tissues, indicating extensive pleiotropy. Our results demonstrate the importance of dense, rich, high-resolution epigenomic annotations for the investigation of complex traits. The authors present EpiMap, a compendium that comprises 10,000 epigenomic maps across more than 800 biosamples for the annotation of genome-wide association study circuitry.

Technologies that profile chromatin modifications at single-cell resolution offer enormous promise for functional genomic characterization, but the sparsity of the measurements and integrating multiple binding maps represent substantial challenges. Here we introduce single-cell (sc)CUT&Tag-pro, a multimodal assay for profiling protein–DNA interactions coupled with the abundance of surface proteins in single cells. In addition, we introduce single-cell ChromHMM, which integrates data from multiple experiments to infer and annotate chromatin states based on combinatorial histone modification patterns. We apply these tools to perform an integrated analysis across nine different molecular modalities in circulating human immune cells. We demonstrate how these two approaches can characterize dynamic changes in the function of individual genomic elements across both discrete cell states and continuous developmental trajectories, nominate associated motifs and regulators that establish chromatin states and identify extensive and cell-type-specific regulatory priming. Finally, we demonstrate how our integrated reference can serve as a scaffold to map and improve the interpretation of additional scCUT&Tag datasets. scCUT&Tag-pro measures a histone modification and surface proteins in single cells.

Genome-wide association studies have identified loci underlying human diseases, but the causal nucleotide changes and mechanisms remain largely unknown. Here we developed a fine-mapping algorithm to identify candidate causal variants for 21 autoimmune diseases from genotyping data. We integrated these predictions with transcription and cis -regulatory element annotations, derived by mapping RNA and chromatin in primary immune cells, including resting and stimulated CD4 + T-cell subsets, regulatory T cells, CD8 + T cells, B cells, and monocytes. We find that ∼90% of causal variants are non-coding, with ∼60% mapping to immune-cell enhancers, many of which gain histone acetylation and transcribe enhancer-associated RNA upon immune stimulation. Causal variants tend to occur near binding sites for master regulators of immune differentiation and stimulus-dependent gene activation, but only 10–20% directly alter recognizable transcription factor binding motifs. Rather, most non-coding risk variants, including those that alter gene expression, affect non-canonical sequence determinants not well-explained by current gene regulatory models. Genome-wide association studies combined with data from epigenomic maps for immune cells have been used to fine-map causal variants for 21 autoimmune diseases; disease risk tends to be linked to single nucleotide polymorphisms in cell-type-specific enhancers, often in regions adjacent to transcription factor binding motifs. Gene variation in autoimmune diseases Hundreds of risk loci for autoimmunity have been identified previously in genome-wide association studies (GWASs), but the implicated loci comprise multiple variants in linkage disequilibrium and rarely alter protein-coding sequence, which complicates their interpretation. This study adopts a new approach for fine mapping causal genetic variants for 21 autoimmune diseases, applying a novel algorithm to GWAS-based loci and integrating genotypic data with epigenomic maps for specialized immune cells. The results implicate a very specific subset of enhancers involved in T-cell stimulation as causal determinants of autoimmune diseases.