Biology subjects

Bickmore, W. A.

Publications and source records attributed to Bickmore, W. A..

At least 19 recordsLinked to original sources

bioRxiv2026

Loop extrusion dynamics and cooperative activation independently regulate enhancer-driven transcription

How enhancers transmit their activation signals to target promoters is a fundamental unanswered question. Gene activation by distal enhancers is affected by the three-dimensional organisation of chromatin driven by cohesin-mediated loop extrusion, but how the dynamic loop extrusion cycle shapes transcriptional outcomes is not fully understood. In addition, genes are typically regulated by multiple enhancers and cases of cooperativity between enhancers have been observed that depend on the relative position of enhancers and gene. The reason for such context-dependent cooperativity is unknown, and whether it is linked to loop extrusion has not been explored. Here, we use synthetic gene activation to show that NIPBL depletion, which decreases loop extrusion rate, reduces long-range activation in a dose-dependent manner. In contrast, WAPL depletion, which reduces cohesin turnover, can both increase and decrease distal gene activation depending on the presence of adjacent CTCF binding sites. These effects on gene activation correlate with the impact on chromatin contacts. Depletion of the co-activator BRD4 also affects long-range activation, but not by changing chromatin contacts. Synthetic activation from two locations results in super-additive responses, which can be predicted by an independently determined response model. These predictions hold for dual activation from proximal and/or distal sites, and with perturbed NIPBL, WAPL, or BRD4. Distal activation therefore appears to be equivalent in nature to proximal activation, and context-dependent cooperativity can arise simply from different level of activation inputs operating on a non-linear response function.

molecular biology↗

bioRxiv2026

Benchmarking tissue- and cell type-of-origin deconvolution in cell-free transcriptomics

Plasma cell-free RNA (cfRNA) reflects tissue- and cell-type-specific activity across pathological states and is a promising biomarker for organ injury and disease. Computational deconvolution methods are widely used to infer organ and cell-type contributions to cfRNA profiles. However, most were originally developed for single-tissue bulk transcriptomes and their performance in body-wide cfRNA settings, where any tissue or cell type can contribute, remains poorly characterised. Here, we present a systematic benchmarking of tissue- and cell type-of-origin deconvolution for plasma cfRNA that considers both methodological and reference-related sources of variability under realistic cfRNA simulation settings. We evaluated seven commonly used deconvolution methods across distinct algorithmic classes and multi-organ reference configurations derived from bulk and single-cell atlases. We assessed performance using simulation frameworks that model multi-organ mixtures, technical noise, and transcript degradation. We further examined deconvolution methods across multiple previously published clinical cfRNA cohorts spanning diverse disease contexts. Across both tissue- and cell-type-level analyses, deconvolution performance was strongly influenced by both method choice and reference parameters. Tissue-of-origin inference was comparatively robust across simulated and clinical datasets, recovering disease-associated organ signals and concordance with biochemical markers. In contrast, cell type-of-origin inference showed greater variability and reduced consistency across analytical settings, leading to divergent interpretations in both simulations and published clinical cfRNA cohorts. Together, these findings demonstrate that methodological and reference-related variability are major sources of uncertainty in cfRNA deconvolution, with tissue-level inference being more robust than cell-type-level inference. Our benchmarking framework provides guidance for reference selection and comparative interpretation in cfRNA deconvolution.

bioinformatics↗

bioRxiv2026

Identifying severe COVID-19 risk variants modulating enhancer reporter activity in lung cells

Common genetic variants contribute to risk for complex human diseases. However, despite thousands of associations, variants modulating disease risk and their functional impact remain largely unknown. This includes SARS-CoV-2 infection, where outcomes range from asymptomatic to fatal. Most host risk variants associated with COVID-19 disease, identified through genome wide association studies, are located in the non-coding genome and may function by altering gene expression in disease-relevant cells and tissues. To address this at scale, we tested >4800 severe COVID-19-associated variants to determine the impact of individual variants and variant combinations on regulatory activity using Self-Transcribing Active Regulatory Region sequencing, a massively-parallel reporter assay, in a lung epithelial cell line (A549). We identify 166 variants within active sequences, of which 29 modulate activity allele-specifically. Evaluating variant combinations, we observe both additive and non-additive effects on regulatory activity. We employ state-of-the-art deep learning models to interpret allele-specific variant effects on regulatory activity and endogenous genomic features. Our work provides a set of prioritised severe COVID-19-associated variants that modulate regulatory activity in lung epithelial cells, candidate transcription factors, and candidate target genes with potential to be disease modifying.

molecular biology↗

bioRxiv2025

Disease-associated genetic variants can cause mutations in tissue-specific protein isoforms

Genetic variants can cause protein-coding mutations that result in disease. Variants are typically interpreted using the reference transcript for a gene. However, most human multi-exon genes encode alternative isoforms. Here, we show that coding exons in alternative isoforms harbour more population variants than exons of reference isoforms, consistent with their reduced evolutionary constraint, and that these variants are more likely to cause nonsynonymous coding mutations. Common and rare disease-associated variants mapping to alternative transcripts can lead to amino acid substitutions predicted to be structurally damaging in the corresponding protein isoform. The alternative transcripts to which disease-associated variants map demonstrate high tissue-specific expression, with many unannotated in reference human genomes, revealed only by long-read RNA-sequencing. As an example, we report an unannotated alternative transcript of the inflammasome regulator DPP9 that is lung epithelium-specific and which harbours a common genetic variant associated with severe COVID-19 and lung fibrosis. The variant causes a p.Leu8Pro missense mutation in an alternative first exon, predicted to disrupt the encoded alpha helix. These findings highlight the importance of considering alternative isoforms, their tissue-specific expression, and full-length transcripts in variant interpretation, with implications for uncovering underappreciated mechanisms of both common and rare disease.

genomics↗

bioRxiv2024

Bystander activation across a TAD boundary supports a cohesin-dependent hub-model for enhancer function

Enhancers in the mammalian genome are able to control their target genes over very large genomic distances, often across intervening genes. Yet the spatial and temporal specificity of developmental gene regulation would seem to demand that enhancers are constrained so that they only activate the correct target gene. The sculpting of three-dimensional chromosome organization, especially that brought about through cohesin-dependent loop extrusion, is thought to be important for facilitating and constraining the action of enhancers. In particular, the boundaries of topologically associating domains (TADs) are thought to delimit regulatory landscapes and prevent enhancers acting on genes close in the linear genome, but located in adjacent TADs. However, there are some examples where enhancers appear to act across TAD boundaries. In these cases it was not determined whether an enhancer can simultaneously activate transcription at genes in its own TAD and in an adjacent TAD. Here, using a combination of mouse developmental genetics, and synthetic activators in stem cells, we show that some Shh enhancers can activate transcription simultaneously, not only of Shh but also at a gene Mnx1 located in an adjacent TAD. This occurs in the context of a chromatin configuration that maintains both genes and the enhancers close together and is influenced by cohesin. To the best of our knowledge this is the first report of two endogenous mammalian genes transcribed simultanously under the control of the same enhancer, and across a TAD boundary. Our data have implications for understanding the design rules of gene regulatory landscapes, and are most consistent with a transcription hub model of enhancer-promoter communication.

genetics↗

bioRxiv2024

PRC2 Promotes Canalisation during Endodermal Differentiation

The genetic circuitry that encodes the developmental programme of mammals is regulated by transcription factors and chromatin modifiers. During early gestation, the three embryonic germ layers are established in a process termed gastrulation. The impact of deleterious mutations in chromatin modifiers such as the polycomb proteins manifests during gastrulation, leading to early developmental failure and lethality in mouse models. Embryonic stem cells have provided key insights into the molecular function of polycomb proteins, but it is impossible to fully appreciate the role of these epigenetic factors in development, or how development is perturbed due to their deficiency, in the steady-state. To address this, we have employed a tractable embryonic stem cell differentiation system to model primitive streak formation and early gastrulation. Using this approach, we find that loss of the repressive polycomb mark H3K27me3 is delayed relative to transcriptional activation, indicating a subordinate rather than instructive role in gene repression. Despite this, chemical inhibition of polycomb enhanced endodermal differentiation efficiency, but did so at the cost of lineage fidelity. These findings highlight the importance of the polycomb system in stabilising the developmental transcriptional response and, in so doing, in shoring up cellular specification.

molecular biology↗

bioRxiv2024

TPR is required for cytoplasmic chromatin fragment formation during senescence

During oncogene-induced senescence there are striking changes in the structure of the nucleus and the organisation of heterochromatin. This is accompanied by activation of a pro-inflammatory gene expression programme - the senescence associated secretory phenotype (SASP) - driven by transcription factors such as NF-{kappa}B. Here we show that TPR, a protein of the nuclear pore complex basket, is required for the very early activation of NF-{kappa}B signalling during the stress-response phase of oncogene-induced senescence. This is prior to activation of the SASP and occurs without affecting NF-{kappa}B nuclear import. We show that TPR is required for the activation of TBK1 signalling at these early stages of senescence and we link this to the formation of heterochromatin-enriched cytoplasmic chromatin fragments thought to bleb off from the nuclear periphery. These cytoplasmic chromatin fragments appear to lack nuclear pore components. Our data suggest that TPR at the nuclear pore is involved in the loss of structural integrity of the nuclear periphery during senescence. We propose that this acts as a trigger for activation of cytoplasmic nucleic acid sensing, NF-{kappa}B signalling, and activation of the SASP, during senescence.

cell biology↗

bioRxiv2023

DNA-binding factor footprints and enhancer RNAs identify functional non-coding genetic variants

Genome-wide association studies (GWAS) have revealed a multitude of candidate genetic variants affecting the risk of developing complex traits and diseases. However, these highlighted regions are typically in the non-coding genome, and uncovering the functional causative single nucleotide variants (SNVs) is challenging. Prioritisation of variants is commonly based on functional genomic annotation with markers of active regulatory elements, but current approaches still poorly predict functional variants. To address this, we systematically analyse six markers of active regulatory elements for their ability to identify functional variants. We benchmark against molecular quantitative trait loci (molQTL) from assays of regulatory element activity that identify allelic effects on DNA-binding factor occupancy, reporter assay expression, and chromatin accessibility. We identify the combination of DNase footprints and divergent enhancer RNA as markers for functional variants. This signature provides high precision, trading-off low recall, thus substantially reducing candidate variant sets to prioritise variants for functional validation. We present this as a framework called FINDER - Functional SNV IdeNtification using DNase footprints and Enhancer RNA, and demonstrate its utility to prioritise variants using leukocyte count trait and analyse variants in linkage disequilibrium with a lead variant to predict a functional variant in asthma. Our findings have implications for prioritising variants from GWAS, in development of predictive scoring algorithms, and for functionally informed fine mapping approaches.

genomics↗

bioRxiv2023

Acetylation of H3K115 at the nucleosome dyad is associated with fragile nucleosomes at active regulatory sites.

Acetylation of lysine residues in the tail domain of histone H3 is well characterized, but lysine residues in the histone globular domain are also acetylated. Histone modifications in globular domain have regulatory potential because of their impact on nucleosome stability but remain poorly characterized. In this study we report the genome-wide distribution of acetylated H3 lysine 115 (H3K115ac), a residue on the lateral surface at the nucleosome dyad, using chromatin immunoprecipitation. In mouse embryonic stem cells, we find that detectable H3K115ac is enriched at the transcription start site of active CpG island promoters, but also at polycomb repressed promoters prior to their subsequent activation during differentiation. By contrast, at enhancers H3K115ac enrichment is dynamic, changing in line with gene activation and chromatin accessibility during differentiation. Most strikingly, we show that H3K115ac is detected as enriched on "fragile" nucleosomes within nucleosome depleted regions at promoters, and active enhancers where it coincides with transcription factor binding, and at CTCF bound sites. These unique features suggest that H3K115ac correlates with, and could contribute, to nucleosome destabilization and that it might be a valuable marker for identifying functionally important regulatory elements in mammalian genomes.

genomics↗

bioRxiv2023

Transcription decouples estrogen-dependent changes in enhancer-promoter contact frequencies and physical proximity

How enhancers regulate their target genes in the context of 3D chromatin organization is extensively studied and models which do not require direct enhancer-promoter contact have recently emerged. Here, we use the activation of estrogen receptor-dependent enhancers in a breast cancer cell line to study enhancer-promoter communication. This allows high temporal resolution tracking of molecular events from hormone stimulation to efficient gene activation. We examine how both enhancer-promoter spatial proximity assayed by DNA fluorescence in situ hybridization, and contact frequencies resulting from chromatin in situ fragmentation and proximity ligation by Capture-C, change dynamically during enhancer-driven gene activation. These orthogonal methods produce seemingly paradoxical results: upon enhancer activation enhancer-promoter contact frequencies increase while spatial proximity decreases. We explore this apparent discrepancy using different estrogen receptor ligands and transcription inhibitors. Our data demonstrate that enhancer-promoter contact frequencies are transcription independent but are influenced by enhancer-bound protein complexes whereas altered enhancer-promoter proximity depends on transcription. Our results emphasize that the relationship between contact frequencies and physical distance in the nucleus, especially over short genomic distances, is not always a simple one.

genomics↗

bioRxiv2023

Dispersal of PRC1 condensates disrupts polycomb chromatin domains and loops

Polycomb-repressive complex 1 (PRC1) has a strong influence on 3D genome organization, mediating local chromatin compaction as well as localized and chromosome-wide clustering of target loci. Several subunits of PRC1 have been shown to have the capacity to form biomolecular condensates through liquid-liquid phase separation in vitro and when tagged and over-expressed in cells. Here, we use 1,6-hexandiol, which disrupts liquid-like condensates, to examine the role of endogenous PRC1 biomolecular condensates on local and chromosome-wide clustering of PRC1-bound loci. Using imaging and chromatin immunoprecipitation combined with deep sequencing analyses, we show that PRC1-mediated chromatin compaction and clustering of targeted genomic loci - at megabase and tens of megabase length scales - can be reversibly disrupted by the addition and subsequent removal of 1,6-hexandiol to mouse embryonic stem cells. Decompaction and dispersal of polycomb domains and clusters cannot be solely attributable to the reduction of PRC1 binding following 1,6-hexandiol treatment as the addition of 2,5-hexandiol has similar effects on binding despite this alcohol not perturbing PRC1-mediated 3D clustering, at least at the sub-megabase and megabase scales. These results suggest that weak hydrophobic interactions between PRC1 molecules, characteristic of liquid-liquid phase separation, have a role in polycomb-mediated genome organization.

molecular biology↗

bioRxiv2022

Ultra-long-range interactions between active regulatory elements

Contacts between enhancers and promoters are thought to relate to their ability to activate transcription. Investigating mechanisms that drive such chromatin interactions is therefore important for understanding gene regulation. Here, we have determined contact frequencies between millions of pairs of cis-regulatory elements from chromosome conformation capture datasets and analysed a collection of hundreds of DNA-binding factors for binding at regions of enriched contacts. This analysis revealed enriched contacts at sites bound by many factors associated with active transcription. We show that active regulatory elements, independent of cohesin and polycomb, interact with each other across distances of 10s of megabases in vertebrate and invertebrate genomes and that interactions correlate and change with activity. However, these ultra-long-range interactions are not dependent on RNA polymerase II transcription or several transcription cofactors. We propose that long-range interactions between cis-regulatory elements are driven by three distinct mechanisms - cohesin-mediated loop extrusion, polycomb contacts, and association between active regions.

genomics↗

bioRxiv2022

Unique functions of two overlapping PAX6 retinal enhancers

Enhancers play a critical role in development by precisely modulating spatial, temporal, and cell type-specific gene expression. Sequence variants in enhancers have been implicated in disease, however establishing the functional consequences of these variants is challenging due to a lack of understanding of precise cell types and developmental stages where the enhancers are normally active. PAX6 is the master regulator of eye development, and has a regulatory landscape containing multiple enhancers driving expression in the eye. Whether these enhancers perform additive, redundant, or distinct functions is unknown. Here we describe the precise cell types and regulatory activity of two PAX6 retinal enhancers, HS5 and NRE. Using a unique combination of live imaging and single-cell RNA sequencing in dual enhancer-reporter zebrafish embryos, we find significant differences in the spatiotemporal activity of these enhancers, and show that HS5 and NRE are active in distinct cell types of the developing retina. Our results show that although overlapping, these enhancers have distinct activities in different cell types and therefore likely non-redundant functions. This work demonstrates that unique cell type-specific functions can be uncovered for apparently similar enhancers when investigated at high resolution in vivo.

genetics↗

bioRxiv2022

Expansion of Ventral Foregut Primes the Enhancer Landscape for Organ Specific Differentiation

Cell proliferation is fundamental for almost all stages of development and differentiation that require an increase cell number. Although cell cycle phase has been associated with differentiation, the actual process of proliferation is not seen as having a specific role. Here we exploit human embryonic stem cell derived endodermal progenitors that we find are an in vitro model for the ventral foregut. These cells exhibit expansion dependent increases in differentiation efficiency to pancreatic progenitors that are linked to organ-specific enhancer priming at the level of chromatin accessibility and the decommissioning of lineage inappropriate enhancers. Our findings suggest that cell proliferation in embryonic development is about more than tissue expansion, it is required to ensure equilibration of gene regulatory networks allowing cells to become primed for future differentiation. The use of expansion of lineage specific intermediates may therefore be an important step in high fidelity in vitro differentiation.

developmental biology↗

bioRxiv2021

Mena regulates the LINC complex to control actin-nuclear lamina associations, trans-nuclear membrane signalling and cancer gene expression

Interactions between cells and the extracellular matrix, mediated by integrin adhesion complexes (IACs), play key roles in cancer progression and metastasis. We investigated systems-level changes in the integrin adhesome during metastatic progression of a patient-derived cutaneous squamous cell carcinoma (cSCC), and found that the actin regulatory protein Mena is enriched in IACs in metastatic cSCC cells. Mena is connected within a subnetwork of actin-binding proteins to the LINC complex component nesprin-2, with which it interacts and co-localises at the nuclear envelope of metastatic cells. Moreover, Mena potentiates the interactions of nesprin-2 with the actin cytoskeleton and the nuclear lamina. CRISPR-mediated Mena depletion causes altered nuclear morphology, reduces tyrosine phosphorylation of the nuclear membrane protein emerin and downregulates expression of the immunomodulatory gene PTX3 via the recruitment of its enhancer to the nuclear periphery. We have uncovered an unexpected novel role for Mena at the nuclear membrane, where it controls the LINC complex, nuclear architecture, chromatin repositioning and cancer gene expression. This is the first description of an adhesion protein regulating gene transcription via direct signalling across the nuclear envelope. O_FIG O_LINKSMALLFIG WIDTH=200 HEIGHT=156 SRC="FIGDIR/small/458340v1_ufig1.gif" ALT="Figure 1"> View larger version (56K): org.highwire.dtl.DTLVardef@14e2251org.highwire.dtl.DTLVardef@af341corg.highwire.dtl.DTLVardef@8624dforg.highwire.dtl.DTLVardef@deeb50_HPS_FORMAT_FIGEXP M_FIG C_FIG

cell biology↗

bioRxiv2021

Cohesin is required for long-range enhancer action

The mammalian genome is organised into topologically associating domains (TADs) that are formed through the process of cohesin-driven loop extrusion1-3 and whose extent is constrained at TAD boundaries by orientation-dependent CTCF binding4-7. The large regulatory landscapes of developmental genes frequently correspond to TADs, leading to the hypothesis that TADs and/or loop extrusion are important for enhancers to act on their cognate gene8,9. However, it has proven hard to interpret the consequences of experimental disruption of TADs or loop-extrusion on gene regulation3,6,10, in part because of the difficulty in distinguishing direct from indirect effects on enhancer-driven gene expression. By coupling acute protein degradation with synthetic activation by targeted transcription factor recruitment in mouse embryonic stem cells, here we show that cohesin, but not CTCF, is required for activation of a target gene by distant distal regulatory elements. Cohesin is not required for activation directly at the promoter or activation from an enhancer located closer to the gene. Our findings support the hypothesis that chromatin compaction mediated by cohesin-mediated loop extrusion allows for genes to be activated by regulatory elements that are located many hundreds of kilobases away in the linear genome but suggests that cohesin is dispensable for more genomically close enhancers.

genetics↗

bioRxiv2019

A Central Role for Canonical PRC1 in Shaping the 3D Nuclear Landscape

Polycomb group (PcG) proteins silence gene expression by chemically and physically modifying chromatin. A subset of PcG target loci are compacted and cluster in the nucleus to form observable bodies; a conformation which is thought to contribute to gene silencing. However, how these interactions influence gross nuclear organisation and their relationship with transcription remains poorly understood. Here we examine the role of Polycomb Repressive Complex 1 (PRC1) in shaping 3D genome organization in mouse embryonic stem cells (mESCs). Using a combination of imaging and Hi-C analyses we show that PRC1-mediated long-range interactions are independent of CTCF and can bridge sites at a megabase scale. Impairment of PRC1 enzymatic activity does not directly disrupt these interactions. We demonstrate that PcG targets coalesce in vivo, and that developmentally induced expression of one of the target loci disrupts this spatial arrangement. Finally, we show that transcriptional activation and the loss of PRC1-mediated interactions are seperable events. These findings provide important insights into the function of PRC1, whilst highlighting the complexity of this regulatory system. HighlightsO_LILoss of RING1B substantially disrupts nuclear architecture. C_LIO_LIPRC1 mediated looping can occur at a Mb scale and is independent of CTCF. C_LIO_LIPolycomb mediated looping is driven by canonical PRC1 complexes. C_LIO_LIMultimeric PRC1-mediated interactions occur in vitro and in vivo. C_LIO_LIDisruption of PRC1-mediated looping is independent of gene activation. C_LI

molecular biology↗

bioRxiv2019

Nuclear organisation and replication timing are coupled through RIF1-PP1 interaction

Three-dimensional genome organisation and replication timing are known to be correlated, however, it remains unknown whether nuclear architecture overall plays an instructive role in the replication-timing program and, if so, how. Here we demonstrate that RIF1 is a molecular hub that co-regulates both processes. Both nuclear organisation and replication timing depend upon the interaction between RIF1 and PP1. However, whereas nuclear architecture requires the full complement of RIF1 and its interaction with PP1, replication timing is not sensitive to RIF1 dosage. RIF1s role in replication timing also extends beyond its interaction with PP1. Availing of this separation-of-function approach, we have therefore identified in RIF1 dual function the molecular bases of the co-dependency of the replication-timing program and nuclear architecture.

genomics↗