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Long non-coding RNAs (lncRNAs) are diverse transcription products emanating from thousands of loci in mammalian genomes. Cis-acting lncRNAs, which constitute a substantial fraction of lncRNAs with an attributed function, regulate gene expression in a manner dependent on the location of their own sites of transcription, at varying distances from their targets in the linear genome. Through various mechanisms, cis-acting lncRNAs have been demonstrated to activate, repress or otherwise modulate the expression of target genes. We discuss the activities that have been ascribed to cis-acting lncRNAs, the evidence and hypotheses regarding their modes of action, and the methodological advances that enable their identification and characterization. The emerging principles highlight lncRNAs as transcriptional units highly adept at contributing to gene regulatory networks and to the generation of fine-tuned spatial and temporal gene expression programmes.Recent methodological advances have driven the identification and characterization of cis-acting long non-coding RNAs (lncRNAs), which modulate target gene expression through various mechanisms and operate at various genomic distances. This Review discusses recent insights into the evolution and functions of these cis-acting lncRNAs.

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.

Spatiotemporal gene expression programmes are orchestrated by transcriptional enhancers, which are key regulatory DNA elements that engage in physical contacts with their target-gene promoters, often bridging considerable genomic distances. Recent progress in genomics, genome editing and microscopy methodologies have enabled the genome-wide mapping of enhancer–promoter contacts and their functional dissection. In this Review, we discuss novel concepts on how enhancer–promoter interactions are established and maintained, how the 3D architecture of mammalian genomes both facilitates and constrains enhancer–promoter contacts, and the role they play in gene expression control during normal development and disease.For appropriate control of gene expression, enhancers must communicate with the right target genes at the right time, typically over large genomic distances. In this Review, Schoenfelder and Fraser discuss our latest understanding of long-range enhancer–promoter crosstalk, including target-gene specificity, interaction dynamics, protein and RNA architects of interactions, roles of 3D genome organization and the pathological consequences of regulatory rewiring.

The assay for transposase-accessible chromatin using sequencing (ATAC-seq) provides a simple and scalable way to detect the unique chromatin landscape associated with a cell type and how it may be altered by perturbation or disease. ATAC-seq requires a relatively small number of input cells and does not require a priori knowledge of the epigenetic marks or transcription factors governing the dynamics of the system. Here we describe an updated and optimized protocol for ATAC-seq, called Omni-ATAC, that is applicable across a broad range of cell and tissue types. The ATAC-seq workflow has five main steps: sample preparation, transposition, library preparation, sequencing and data analysis. This protocol details the steps to generate and sequence ATAC-seq libraries, with recommendations for sample preparation and downstream bioinformatic analysis. ATAC-seq libraries for roughly 12 samples can be generated in 10 h by someone familiar with basic molecular biology, and downstream sequencing analysis can be implemented using benchmarked pipelines by someone with basic bioinformatics skills and with access to a high-performance computing environment.A protocol for generating chromatin accessibility profiles from a broad variety of cell and tissue types, including a step-by-step workflow for library preparation and guidelines for data processing and downstream analysis.

Cleavage under targets and release using nuclease (CUT&RUN) is an epigenomic profiling strategy in which antibody-targeted controlled cleavage by micrococcal nuclease releases specific protein-DNA complexes into the supernatant for paired-end DNA sequencing. As only the targeted fragments enter into solution, and the vast majority of DNA is left behind, CUT&RUN has exceptionally low background levels. CUT&RUN outperforms the most widely used chromatin immunoprecipitation (ChIP) protocols in resolution, signal-to-noise ratio and depth of sequencing required. In contrast to ChIP, CUT&RUN is free of solubility and DNA accessibility artifacts and has been used to profile insoluble chromatin and to detect long-range 3D contacts without cross-linking. Here, we present an improved CUT&RUN protocol that does not require isolation of nuclei and provides high-quality data when starting with only 100 cells for a histone modification and 1,000 cells for a transcription factor. From cells to purified DNA, CUT&RUN requires less than a day at the laboratory bench and requires no specialized skills.

Studies of 3D chromatin organization have suggested that chromosomes are hierarchically organized into large compartments composed of smaller domains called topologically associating domains (TADs). Recent evidence suggests that compartments are smaller than previously thought and that the transcriptional or chromatin state is responsible for interactions leading to the formation of small compartmental domains in all organisms. In vertebrates, CTCF forms loop domains, probably via an extrusion process involving cohesin. CTCF loops cooperate with compartmental domains to establish the 3D organization of the genome. The continuous extrusion of the chromatin fibre by cohesin may also be responsible for the establishment of enhancer–promoter interactions and stochastic aspects of the transcription process. These observations suggest that the 3D organization of the genome is an emergent property of chromatin and its components, and thus may not be only a determinant but also a consequence of its function.

The Omni-ATAC protocol improves the signal-to-background ratio in chromatin accessibility profiles and is suitable for a range of cell lines and primary cell types, as well as frozen tissue. We present Omni-ATAC, an improved ATAC-seq protocol for chromatin accessibility profiling that works across multiple applications with substantial improvement of signal-to-background ratio and information content. The Omni-ATAC protocol generates chromatin accessibility profiles from archival frozen tissue samples and 50-μm sections, revealing the activities of disease-associated DNA elements in distinct human brain structures. The Omni-ATAC protocol enables the interrogation of personal regulomes in tissue context and translational studies.

Cellular function in tissue is dependent on the local environment, requiring new methods for spatial mapping of biomolecules and cells in the tissue context 1 . The emergence of spatial transcriptomics has enabled genome-scale gene expression mapping 2 – 5 , but the ability to capture spatial epigenetic information of tissue at the cellular level and genome scale is lacking. Here we describe a method for spatially resolved chromatin accessibility profiling of tissue sections using next-generation sequencing (spatial-ATAC-seq) by combining in situ Tn5 transposition chemistry 6 and microfluidic deterministic barcoding 5 . Profiling mouse embryos using spatial-ATAC-seq delineated tissue-region-specific epigenetic landscapes and identified gene regulators involved in the development of the central nervous system. Mapping the accessible genome in the mouse and human brain revealed the intricate arealization of brain regions. Applying spatial-ATAC-seq to tonsil tissue resolved the spatially distinct organization of immune cell types and states in lymphoid follicles and extrafollicular zones. This technology progresses spatial biology by enabling spatially resolved chromatin accessibility profiling to improve our understanding of cell identity, cell state and cell fate decision in relation to epigenetic underpinnings in development and disease. Spatial-ATAC-seq—spatially resolved chromatin accessibility profiling of tissue sections using next-generation sequencing—delineated tissue-region-specific epigenetic landscapes in mouse embryos and identified gene regulators involved in the development of the central nervous system and the lymphoid tissue.

Key Points Chromosomes fold in a hierarchy of structures with increasing complexity, from nucleosomes and chromatin fibres to chromatin loops, chromosome domains, chromosome compartments and, finally, chromosome territories A limited set of components, including architectural proteins, chromatin regulators and non-coding RNAs (ncRNAs) regulate three-dimensional (3D) chromosome organization Chromosome architecture is globally stable, but able to receive regulatory cues to undergo local and global reorganization in specific portions of the genome 3D organization can have causative roles in the regulation of gene expression, whereas in other cases it is modulated by gene expression 3D chromatin structure transitions are typical of development and cell differentiation, and are often dysregulated in disease processes Chromosome architecture evolved considerably across evolutionary kingdoms, but remains robust in species of the distal branches of the evolutionary tree In this article the authors review current knowledge on chromatin architecture and the molecular mechanisms that underlie it. They discuss how three-dimensional (3D) organization of chromatin relates to gene expression, development and disease, and consider its effect on genome evolution. Understanding how chromatin is organized within the nucleus and how this 3D architecture influences gene regulation, cell fate decisions and evolution are major questions in cell biology. Despite spectacular progress in this field, we still know remarkably little about the mechanisms underlying chromatin structure and how it can be established, reset and maintained. In this Review, we discuss the insights into chromatin architecture that have been gained through recent technological developments in quantitative biology, genomics and cell and molecular biology approaches and explain how these new concepts have been used to address important biological questions in development and disease.

Many chromatin features play critical roles in regulating gene expression. A complete understanding of gene regulation will require the mapping of specific chromatin features in small samples of cells at high resolution. Here we describe Cleavage Under Targets and Tagmentation (CUT&Tag), an enzyme-tethering strategy that provides efficient high-resolution sequencing libraries for profiling diverse chromatin components. In CUT&Tag, a chromatin protein is bound in situ by a specific antibody, which then tethers a protein A-Tn5 transposase fusion protein. Activation of the transposase efficiently generates fragment libraries with high resolution and exceptionally low background. All steps from live cells to sequencing-ready libraries can be performed in a single tube on the benchtop or a microwell in a high-throughput pipeline, and the entire procedure can be performed in one day. We demonstrate the utility of CUT&Tag by profiling histone modifications, RNA Polymerase II and transcription factors on low cell numbers and single cells. Understanding gene regulation will require mapping specific chromain features in a small number of cells at high resolution. Here the authors describe CUT&Tag, which uses antibody-mediated tethering of Tn5 transposase to a chromatin protein to generate high resolution libraries.