Transcription factors (TFs) are central to gene regulation and play critical roles in development, cellular homeostasis and disease. The ability to accurately measure TF activity is essential to understanding how TFs respond to signals and regulate target genes. In one commonly used approach, activities of TFs are computationally inferred from genome-wide chromatin accessibility data (ATAC-seq). However, it has remained unclear how well these inferences reflect actual regulatory activity of TFs. An alternative approach employs a collection of synthetic reporters that are designed to each probe the regulatory activity of a single TF. In this study, we systematically compared TF activities as inferred by ATAC-seq with those measured by multiplexed reporters, across diverse perturbations known to alter specific TF activities. We observed considerable overlap between the two methods, but also notable discrepancies. Our findings suggest that reporter assays and chromatin-based inference capture distinct aspects of TF function: reporter assays are more sensitive to signal-responsive TFs, while ATAC-seq better detects chromatin-modifying TFs.

DNA replication timing (RT) often correlates with transcription during cell fate transitions, yet notable exceptions indicate a complex relationship. Using a reductionist system in mouse embryonic stem cells, we manipulate transcriptional length and strength at a single locus upstream of the silent, late-replicating Pleiotrophin (Ptn) gene. Small reporter genes driven by two of four promoters advance RT, whereas all promoters advance RT when driving the 96-kb endogenous Ptn gene. Inducible transcription of Ptn, but not the reporter, triggers a rapid and reversible RT advance, providing a system to manipulate RT independent of differentiation. Strikingly, deletion of the Ptn promoter and enhancers abolishes transcription yet does not prevent the developmental RT switch to early replication during neural differentiation. These findings, supported by parallel genome-wide analyses during differentiation, demonstrate that transcriptional elongation can causally advance RT in a rate-dependent and context-specific manner, but that transcription is neither necessary nor sufficient for RT advancement. Our results provide a solid empirical base with which to re-evaluate decades of seemingly contradictory literature.

Transcription factors (TFs) regulate the genome in response to signaling events. Detecting their activity is crucial to deciphering the regulatory networks of cells. Here, we present a protocol for multiplexed TF activity detection using a barcoded plasmid library of optimized "prime" TF reporters in cultured cells. We describe steps for library transfection, RNA processing for barcode sequencing, and a computational pipeline for analyzing differential TF activity, enabling high-throughput and quantitative TF profiling. For complete details on the use and execution of this protocol, please refer to Trauernicht et al.1.

Promoters are the core regulatory elements of all genes. Their activity ensures the correct transcription level of each individual gene, which is essential for cellular homeostasis and responses to a wide range of signals. One of the major challenges in genomics is to build computational models that accurately predict genome-wide gene expression from the sequences of regulatory elements1. Here we present promoter activity regulatory model (PARM), a cell-type-specific deep-learning model trained on specially designed massively parallel reporter assays (MPRAs) that query human promoter sequences. PARM is experimentally and computationally lightweight so that cell-type-specific and condition-specific models can be generated that reliably predict autonomous promoter activity across the genome from the DNA sequence alone. PARM can also design purely synthetic strong promoters. We leveraged PARM to systematically identify binding sites of transcription factors that probably contribute to the activity of each natural human promoter and to detect the rewiring of these regulatory interactions after various stimuli to the cells. We also uncovered and experimentally confirmed substantial positional preferences of transcription factors that differ between activating and repressive regulatory functions and a complex grammar of motif-motif interactions. Our approach provides a highly economic strategy towards a deeper understanding of the dynamic regulation of human promoters by transcription factors.

Transcription of genes is regulated by DNA elements such as promoters and enhancers, the activity of which are in turn controlled by many transcription factors. Owing to the highly complex combinatorial logic involved, it has been difficult to construct computational models that predict gene activity from DNA sequence. Recent advances in deep learning techniques applied to data from epigenome mapping and high-throughput reporter assays have made substantial progress towards addressing this complexity. Such models can capture the regulatory grammar with remarkable accuracy and show great promise in predicting the effects of non-coding variants, uncovering detailed molecular mechanisms of gene regulation and designing synthetic regulatory elements for biotechnology. Here, we discuss the principles of these approaches, the types of training data sets that are available and the strengths and limitations of different approaches. Barbadilla-Martínez et al. review recent progress in deep-learning-based sequence-to-expression models, which predict gene expression levels solely from DNA sequence. These models are providing new insights into the complex combinatorial logic underlying cis-regulatory control of gene expression.

Genes are often activated by enhancers located at large genomic distances, and the importance of this positioning is poorly understood. By relocating promoter-reporter constructs into thousands of alternative positions within a single locus, we dissected the positional relationship between the mouse Sox2 gene and its distal enhancer. This revealed an intricate, sharply confined activation landscape in which the native Sox2 gene occupies an optimal position for its activation. Deletion of the gene relaxes this confinement and broadly increases reporter activity. The confining effect of the Sox2 gene is partially conferred by its ~1-kilobase coding region. Our local relocation approach provides high-resolution functional maps of a genomic locus and reveals that a gene can strongly constrain the realm of influence of its enhancer.

Lamina-associated domains (LADs) are megabase-sized genomic regions that interact with the nuclear lamina (NL). It is not yet understood how their interactions with the NL are encoded in their DNA. Here we designed an efficient LAD 'scrambling' approach, based on transposon-mediated local hopping of loxP recombination sites, to generate series of large deletions and inversions that span LADs and flanking sequences. Mapping of NL interactions in these rearrangements revealed that, in mouse embryonic stem cells, a single LAD contacts the NL through multiple regions that act cooperatively or redundantly; some have more affinity for the NL than others and can pull neighboring sequences to the NL. Genes drawn toward the NL showed often but not always reduced expression and increased H3K9me3 levels. Furthermore, neighboring LADs can cooperatively interact with the NL when placed close enough to each other. These results elucidate principles that govern the positioning of megabase-sized genomic regions inside the cell nucleus.

Lamina-associated domains (LADs) are megabase-sized genomic regions anchored to the nuclear lamina (NL). Factors controlling the interactions of the genome with the NL have largely remained elusive. Here, we identified DNA topoisomerase 2 beta (TOP2B) as a regulator of these interactions. TOP2B binds predominantly to inter-LAD (iLAD) chromatin and its depletion results in a partial loss of genomic partitioning between LADs and iLADs, suggesting that this enzyme might protect specific iLADs from interacting with the NL. TOP2B depletion affects LAD interactions with lamin B receptor (LBR) more than with lamins. LBR depletion phenocopies the effects of TOP2B depletion, despite the different positioning of the two proteins in the genome. This suggests a complementary mechanism for organizing the genome at the NL. Indeed, co-depletion of TOP2B and LBR causes partial LAD/iLAD inversion, reflecting changes typical of oncogene-induced senescence. We propose that a coordinated axis controlled by TOP2B in iLADs and LBR in LADs maintains the partitioning of the genome between the NL and the nuclear interior.

DNA replication timing (RT) is correlated with transcription during cell fate changes but there are many exceptions and our understanding of this relationship suffers from a paucity of reductionist approaches. Here, we manipulated length and strength of transcription in hybrid-genome mouse embryonic stem cells (mESCs) at a single locus upstream of the silent, late replicating, Pleiotrophin (Ptn) gene, directly comparing RT to nascent transcription rates at engineered vs. wild-type alleles. First, we inserted four reporter genes that differ only in their promoter. Two promoters transcribed the reporter gene at high rates and advanced RT. The other two transcribed at lower rates and did not advance RT. Since these promoters may prove useful in applications where effects on RT are undesirable, we confirmed the inability of one of them to advance RT at numerous ectopic sites. We next juxtaposed these same four promoters upstream of the Ptn transcription start site where they all transcribed the 96kb Ptn gene and advanced RT to different extents correlated with transcription rates. Indeed, a doxycycline-responsive promoter, which could not advance RT when induced as a small reporter gene, elicited a rapid and reversible RT advance proportional to the rate of transcription, providing direct evidence that transcription itself can advance RT. However, deletion of the Ptn promoter and enhancer, followed by directed differentiation to neural precursors, eliminated induction of transcription throughout the entire Ptn replication domain, without preventing the switch to early replication. Our results provide a solid empirical base with which to re-evaluate many decades of literature, demonstrating that length and strength of transcription is sufficient but not necessary to advance RT. Our results also provide a robust system in which to rapidly effect an RT change, permitting mechanistic studies of the role of transcription in RT and the consequences of RT changes to epigenomic remodeling.

Lamina-associated domains (LADs) are large genomic regions that contact the nuclear lamina (NL). Double-strand breaks (DSBs) in LADs are known to be repaired more slowly and with different pathway preferences compared to other chromatin contexts. However, little is known about the chromatin changes at LADs that occur during DSB repair. Here, we report that a single DSB inside a LAD can cause detachment from the NL over several megabases. This profound spatial rearrangement is transient and reverts within 48 hours. Preventing this detachment slows down repair kinetics and renders repair incomplete, indicating that NL detachment is required for efficient repair of DSBs in LADs. NL detachment is dependent on ψH2AX and ATM, while it is antagonized by DNAPKcs activity. Remarkably, ψH2AX also antagonizes NL interactions at chromosome ends. Taken together, our data indicate that ψH2AX accumulation in LADs induces large scale rewiring of genome-NL interactions, allowing for efficient repair of DSBs. ### Competing Interest Statement The authors have declared no competing interest. ZonMW, TOP grant 91215067 European Research Council (ERC), Advanced Grant 694466 NWO, Zwaartekracht MSCA-IF, 838555, Next generation EU-MUR MSCA Young Researcher

The dynamic three-dimensional (3D) organization of the human genome (the 4D nucleome) is linked to genome function. Here we describe efforts by the 4D Nucleome Project1 to map and analyse the 4D nucleome in widely used H1 human embryonic stem cells and immortalized fibroblasts (HFFc6). We produced and integrated diverse genomic datasets of the 4D nucleome, each contributing unique observations, which enabled us to assemble extensive catalogues of more than 140,000 looping interactions per cell type, to generate detailed classifications and annotations of chromosomal domain types and their subnuclear positions, and to obtain single-cell 3D models of the nuclear environment of all genes including their long-range interactions with distal elements. Through extensive benchmarking, we describe the unique strengths of different genomic assays for studying the 4D nucleome, providing guidelines for future studies. Three-dimensional models of population-based and individual cell-to-cell variation in genome structure showed connections between chromosome folding, nuclear organization, chromatin looping, gene transcription and DNA replication. Finally, we demonstrate the use of computational methods to predict genome folding from DNA sequence, which will facilitate the discovery of potential effects of genetic variants, including variants associated with disease, on genome structure and function.

Models of nuclear genome organization often propose a binary division into active versus inactive compartments yet typically overlook nuclear bodies. Here, we integrated analysis of sequencing and image-based data to compare genome organization in four human cell types relative to three different nuclear locales: the nuclear lamina, nuclear speckles, and nucleoli. Although gene expression correlates mostly with nuclear speckle proximity, DNA replication timing correlates with proximity to multiple nuclear locales. Speckle attachment regions emerge as DNA replication initiation zones whose replication timing and gene composition vary with their attachment frequency. Most facultative LADs retain a partially repressed state as iLADs, despite their positioning in the nuclear interior. Knock out of two lamina proteins, Lamin A and LBR, causes a shift of H3K9me3-enriched LADs from lamina to nucleolus, and a reciprocal relocation of H3K27me3-enriched partially repressed iLADs from nucleolus to lamina. Thus, these partially repressed iLADs appear to compete with LADs for nuclear lamina attachment with consequences for replication timing. The nuclear organization in adherent cells is polarized with nuclear bodies and genomic regions segregating both radially and relative to the equatorial plane. Together, our results underscore the importance of considering genome organization relative to nuclear locales for a more complete understanding of the spatial and functional organization of the human genome.

Interphase chromosomes are mainly shaped by loop extrusion and compartmentalisation mechanisms. However, their temporal component and cause-effect relationships remain largely unknown. In this study, we use acute degradation of WAPL, CTCF and cohesin in mouse embryonic stem cells to investigate the dynamics of loop extrusion and its relationship to compartmentalisation. Stabilisation of cohesin on chromatin by depletion of WAPL results in the formation of extended loops and promotes looping between non-convergent CTCF sites. Loss of WAPL also results in a rapid decrease in compartmentalisation, which is reversed by subsequent removal of cohesin, directly demonstrating the opposite role of extrusion on compartmentalisation. Using combined depletion of WAPL and CTCF, we identify fountains, a feature of chromosome organisation that emanates from enhancer regions and exhibits strong cohesin binding. Fountains form rapidly after mitosis and early in mammalian development. Cohesin depletion confirms that fountains are cohesin dependent, and their disruption leads to the downregulation of fountain-proximal genes, suggesting a role in gene regulation. Taken together, by exploiting the temporal precision of acute protein depletion, our study reveals fountains as an extrusion-mediated, fast-forming feature of 3D genome organisation.

DNA double-strand breaks are repaired by multiple pathways, including non-homologous end-joining (NHEJ) and microhomology-mediated end-joining (MMEJ). The balance of these pathways is dependent on the local chromatin context, but the underlying mechanisms are poorly understood. By combining knockout screening with a dual MMEJ:NHEJ reporter inserted in 19 different chromatin environments, we identified dozens of DNA repair proteins that modulate pathway balance dependent on the local chromatin state. Proteins that favor NHEJ mostly synergize with euchromatin, while proteins that favor MMEJ generally synergize with distinct types of heterochromatin. Examples of the former are BRCA2 and POLL, and of the latter the FANC complex and ATM. Moreover, in a diversity of human cancer types, loss of several of these proteins alters the distribution of pathway-specific mutations between heterochromatin and euchromatin. Together, these results uncover a complex network of proteins that regulate MMEJ:NHEJ balance in a chromatin context-dependent manner. DNA double-strand breaks are repaired by multiple pathways. The balance of these pathways depends on the local chromatin context, but the underlying mechanisms are poorly understood. Here the authors uncover a network of proteins that regulate pathway balance in a chromatin context-dependent manner.

Genes are often activated by enhancers located at large genomic distances. The importance of this positioning is poorly understood. By relocating promoter-reporter constructs into >1,000 alternative positions within a single locus, we dissected the positional relationship between the mouse Sox2 gene and its distal enhancer. This revealed an intricate, sharply confined activation landscape, in which the native Sox2 gene occupies an optimal position for its activation. Deletion of the gene relaxes this confinement and broadly increases reporter activity. Surprisingly, the confining effect of the Sox2 gene is partially conferred by its ~1 kb coding region. Our local relocation approach provides high-resolution functional maps of a genomic locus and reveals that a gene can strongly constrain the realm of influence of its enhancer. ### Competing Interest Statement The authors have declared no competing interest.

Lamina-associated domains (LADs) are megabase-sized genomic regions that interact with the nuclear lamina (NL). It is not yet understood how their interactions with the NL are encoded in their DNA. Here, we designed an efficient LAD “scrambling” approach, based on transposon-mediated local hopping of loxP recombination sites, to generate series of large deletions and inversions that span LADs and flanking sequences. Mapping of NL interactions in these rearrangements revealed that a single LAD contacts the NL through multiple regions that act cooperatively or redundantly; some have more affinity for the NL than others and can pull neighbouring sequences to the NL. Genes drawn towards the NL showed often, but not always, reduced expression and increased H3K9me3 levels. Furthermore, neighbouring LADs can cooperatively interact with the NL when placed close enough to each other. These results elucidate principles that govern the positioning of megabase-sized genomic regions inside the cell nucleus. Highlights ### Competing Interest Statement The authors have declared no competing interest.

AbstractLamina-associated domains (LADs) are large chromatin regions that are associated with the nuclear lamina (NL) and form a repressive environment for transcription. The molecular players that mediate gene repression in LADs are currently unknown. Here, we performed FACS-based whole-genome genetic screens in human cells using LAD-integrated fluorescent reporters to identify such regulators. Surprisingly, the screen identified very few NL proteins, but revealed roles for dozens of known chromatin regulators. Among these are the negative elongation factor (NELF) complex and interacting factors involved in RNA polymerase pausing, suggesting that regulation of transcription elongation is a mechanism to repress transcription in LADs. Furthermore, the chromatin remodeler complex BAF and the activation complex Mediator can work both as activators and repressors in LADs, depending on the local context and possibly by rewiring heterochromatin. Our data indicate that the fundamental regulators of transcription and chromatin remodeling, rather than interaction with NL proteins, play a major role in transcription regulation within LADs.

Genes are often regulated by multiple enhancers. It is poorly understood how the individual enhancer activities are combined to control promoter activity. Anecdotal evidence has shown that enhancers can combine sub-additively, additively, synergistically, or redundantly. However, it is not clear which of these modes are more frequent in mammalian genomes. Here, we systematically tested how pairs of enhancers activate promoters using a three-way combinatorial reporter assay in mouse embryonic stem cells. By assaying about 69,000 enhancer-enhancer-promoter combinations we found that enhancer pairs generally combine near-additively. This behaviour was conserved across seven developmental promoters tested. Surprisingly, these promoters scale the enhancer signals in a non-linear manner that depends on promoter strength. A housekeeping promoter showed an overall different response to enhancer pairs, and a smaller dynamic range. Thus, our data indicate that enhancers mostly act additively, but promoters transform their collective effect non-linearly.