Biology subjects

Murat, P.

Publications and source records attributed to Murat, P..

10 recordsLinked to original sources

bioRxiv2026

DNA supercoiling links transcription and chromatin architecture during human stem cell differentiation

Transcription imposes torsional stress on chromatin, leading to over- or under-winding of the DNA helix. Yet, how supercoiling evolves during dynamic changes in gene expression, and how it influences three-dimensional chromatin contacts in the densely packed human genome, remains unclear. Here, we map genome-wide negative supercoiling and chromatin interactions at high resolution in human embryonic stem cells, using the transcriptional changes that drive differentiation to explore their interplay at multiple scales. We demonstrate that gene activation increases negative supercoiling despite enhanced topoisomerase recruitment. Moreover, elevated negative supercoiling correlates with increased DNA contacts within domains at multiple scales, from genes to topologically associating domains, consistent with transcription-generated torsional stress enhancing contact frequency. Thus, negative supercoiling likely contributes to the genome architectural remodelling that accompanies the execution of developmental programs.

genomics↗

bioRxiv2025

Generating long deletions across the genome with pooled paired prime editing screens

Engineered deletions are a powerful probe for studying genome architecture, function, and regulation. Yet, the lack of effective methods to create them in large numbers and at multi-kilobase scale has rendered interrogating all the gigabases of human DNA elusive. Prime editing based approaches are promising contenders to fill this gap, but have not been adopted for large-scale pooled screening so far. Here, we performed the first high-throughput paired prime editing deletion screens. To establish the technology, we generated 3,802 deletions of up to 1.2 Mb in a reporter locus in two human cell lines, and identified key determinants of paired prime editing efficiency to be deletion length, predicted pegRNA efficacy, and contact frequency. We used these learnings to generate therapeutically important deletions at rates that are expected to give clinical benefits for retinitis pigmentosa and Duchenne muscular dystrophy. Combining several technological advances, we then performed the first pooled paired prime editing screen to delete over 10,471 sequences of median length 1.1 kb that target 149 genes across the genome. Our screens were high quality, recovering 75% of positive controls. We discovered 462 non-coding regions with fitness effects, and validated deletions with impact as well as tolerated ones in regions with functional annotations. Our screens are the largest pooled characterization of precise deletions to date, demonstrating that prime deletion screens can perturb the genome at scale, and highlighting that most non-coding DNA around essential genes is dispensable for cell growth in one condition.

genomics↗

bioRxiv2025

Resolution of a human super-enhancer by targeted genome randomisation

Human gene expression is controlled from distance via enhancers, which can form longer super-enhancer-regions of intense regulatory activity. Whether super-enhancers constitute a separate regulatory paradigm remains unclear, largely due to the difficulty of dissecting the contributions and interactions of individual elements within their natural chromosomal context. To address this challenge, we developed enhancer scrambling, a high-throughput strategy to generate stochastic inversions and deletions of targeted enhancer regions by combining CRISPR prime editing insertion of symmetrical loxP sites with Cre recombinase-induced rearrangements. We applied our approach to dissect a distal super-enhancer of the OTX2 gene, generating up to 134 alternative regulatory configurations in a single experiment, and establishing how they drive gene expression and chromatin accessibility, as well as the individual contributions of its elements to this activity. Surprisingly, the presence of the sequence containing a single DNase I hypersensitive site predominantly controls OTX2 expression. Our findings highlight that enhancer-driven regulation of some highly expressed, cell-type-specific genes can rely on an individual element within a cluster of non-interacting, dispensable components, and suggest a simple functional core to a subset of super-enhancers. The targeted randomisation method to scramble enhancers can scale to resolve many super-enhancers and human gene regulatory landscapes.

synthetic biology↗

bioRxiv2024

DNA replication initiation drives focal mutagenesis and rearrangements in human cancers

The rate and pattern of mutagenesis in cancer genomes is significantly influenced by DNA accessibility and active biological processes. Here we show that efficient sites of replication initiation drive and modulate specific mutational processes in cancer. Sites of replication initiation impede nucleotide excision repair in melanoma and are off-targets for activation-induced deaminase (AICDA) activity in lymphomas. Using ductal pancreatic adenocarcinoma as a cancer model, we demonstrate that the initiation of DNA synthesis is error-prone at G-quadruplex-forming sequences in tumours displaying markers of replication stress, resulting in a previously recognised but uncharacterised mutational signature. Finally, we demonstrate that replication origins serve as hotspots for genomic rearrangements, including structural and copy number variations. These findings reveal replication origins as functional regulators of tumour biology and demonstrate that replication initiation both passively and actively drives focal mutagenesis in cancer genomes.

genetics↗

bioRxiv2021

Replication origins drive genetic and phenotypic variation in humans

DNA replication starts with the activation of the replicative helicases, polymerases and associated factors at thousands of origins per S-phase 1. Due to local torsional constraints generated during licensing 2 and the switch between polymerases of distinct fidelity and proofreading ability following firing 3,4, origin activation has the potential to induce DNA damage and mutagenesis. However, whether sites of replication initiation exhibit a specific mutational footprint has not yet been established. Here we demonstrate that mutagenesis is increased at early and highly efficient origins. The elevated mutation rate observed at these sites is caused by two distinct mutational processes consistent with formation of DNA breaks at the origin itself and local error-prone DNA synthesis in the immediate vicinity of the origin. We demonstrate that these replication-dependent mutational processes create the skew in base composition observed at human replication origins. Further, we show that mutagenesis associated with replication initiation exerts an influence on phenotypic diversity in human populations disproportionate to the origins genomic footprint: by increasing mutational loads at gene promoters and splice junctions the presence of an origin influences both gene expression and mRNA isoform usage. These findings have important implications for our understanding of the mutational processes that sculpt the human genome.

genetics↗

bioRxiv2021

Determination of human DNA replication origin position and efficiency reveals principles of initiation zone organisation

Replication of the human genome initiates within broad zones of ~ 150 kb. The extent to which firing of individual DNA replication origins within initiation zones is spatially stochastic or localised at defined sites remains a matter of debate. A thorough characterisation of the dynamic activation of origins within initiation zones is hampered by the lack of a high-resolution map of both their position and efficiency. To address this shortcoming, we describe a modification of initiation site sequencing (ini-seq) based on density substitution. Newly-replicated DNA is rendered heavy-light (HL) by incorporation of BrdUTP, unreplicated DNA remaining light-light (LL). Replicated HL-DNA is separated from unreplicated LL-DNA by equilibrium density gradient centrifugation, then both fractions are subjected to massive parallel sequencing. This allows precise mapping of 23,905 replication origins simultaneously with an assignment of a replication initiation efficiency score to each. We show that origin firing within initiation zones is not randomly distributed. Rather, origins are arranged hierarchically with a set of very highly efficient origins marking zone boundaries. We propose that these origins explain much of the early firing activity arising within initiation zones, helping to unify the concept of replication initiation zones with the identification of discrete replication origin sites.

genomics↗

bioRxiv2020

DNA polymerase stalling at structured DNA constrains the expansion of Short Tandem Repeats

BackgroundShort tandem repeats (STRs) contribute significantly to de novo mutagenesis, driving phenotypic diversity and genetic disease. Although highly diverse, their repetitive sequences induce DNA polymerase slippage and stalling, leading to length and sequence variation. However, current studies of DNA synthesis through STRs are restricted to a handful of selected sequences, limiting our broader understanding of their evolutionary behaviour and hampering the characterisation of the determinants of their abundance and stability in eukaryotic genomes. ResultsWe perform a comprehensive analysis of DNA synthesis at all STR permutations and interrogate the impact of STR sequence and secondary structure on their genomic representation and mutability. To do so, we developed a high-throughput primer extension assay that allows monitoring of the kinetics and fidelity of DNA synthesis through 20,000 sequences comprising all STR permutations in different lengths. By combining these measurements with population-scale genomic data, we show that the response of a model replicative DNA polymerase to variously structured DNA is sufficient to predict the complex genomic behaviour of STRs, including abundance and mutational constraints. We demonstrate that DNA polymerase stalling at DNA structures induces error-prone DNA synthesis, which constrains STR expansion. ConclusionsOur data support a model in which STR length in eukaryotic genomes results from a balance between expansion due to polymerase slippage at repeated DNA sequences and point mutations caused by error-prone DNA synthesis at DNA structures.

evolutionary biology↗

bioRxiv2019

Timeless couples G quadruplex detection with processing by DDX11 during DNA replication

Regions of the genome with the potential to form secondary structure pose a frequent and significant impediment to DNA replication and must be actively managed in order to preserve genetic and epigenetic integrity. The fork protection complex (FPC), a conserved group of replisome-associated proteins including Timeless, Tipin, and Claspin, plays an important role in maintaining efficient replisome activation, ensuring optimum fork rates, sister chromatid cohesion and checkpoint function. It also helps maintain the stability of sequences prone to secondary structure formation through an incompletely understood mechanism. Here, we report a previously unappreciated DNA binding domain in the C-terminus of Timeless, which exhibits specific binding to G quadruplex (G4) structures. We show that, in vivo, both the C-terminus of Timeless and the DDX11 helicase act collaboratively to ensure processive replication of G4 structures to prevent genetic and epigenetic instability.

molecular biology↗

bioRxiv2017

5-Formylcytosine controls nucleosome positioning through covalent histone-DNA interaction

Nucleosomes are the basic unit of chromatin that ensure genome integrity and control access to the genetic information. The organization of nucleosomes is influenced by the underlying DNA sequence itself, transcription factors or other transcriptional machinery associated proteins and chromatin remodeling complexes (1-4). Herein, we show that the naturally occurring DNA modification, 5-formylcytosine (5fC) contributes to the positioning of nucleosomes. We show that the ability of 5fC to position nucleosomes in vitro is associated with the formation of covalent interactions between histone residues and 5fC in the form of Schiff bases. We demonstrate that similar interactions can occur in a cellular environment and define their specific genomic loci in mouse embryonic stem cells. Collectively, our findings identify 5fC as a determinant of nucleosomal organization in which 5fC plays a role in establishing distinct regulatory regions that are linked to gene expression Our study provides a previously unknown molecular mechanism, involving the formation of reversible-covalent bonds between chromatin and DNA that supports a molecular linkage between DNA sequence, DNA base modification and chromatin structure.

genomics↗

bioRxiv2017

RNA G-quadruplexes mark repressive upstream open reading frames in human mRNAs

RNA secondary structures in the 5 untranslated regions (UTRs) of mRNAs have been characterised as key determinants of translation initiation. However the role of non-canonical secondary structures, such as RNA G-quadruplexes (rG4s), in modulating translation of human mRNAs and the associated mechanisms remain largely unappreciated. Here we use a ribosome profiling strategy to investigate the translational landscape of human mRNAs with structured 5 untranslated regions (5-UTR). We found that inefficiently translated mRNAs, containing rG4-forming sequences in their 5-UTRs, have an accumulation of ribosome footprints in their 5-UTRs. We show that rG4-forming sequences are determinants of 5-UTR translation, suggesting that the folding of rG4 structures thwarts the translation of protein coding sequences (CDS) by stimulating the translation of repressive upstream open reading frames (uORFs). To support our model, we demonstrate that depletion of two rG4s-specialised DEAH-box helicases, DHX36 and DHX9, shifts translation towards rG4-containing uORFs reducing the translation of selected transcripts comprising proto-oncogenes, transcription factors and epigenetic regulators. Transcriptome-wide identification of DHX9 binding sites using individual-nucleotide resolution UV crosslinking and immunoprecipitation (iCLIP) demonstrate that translation regulation is mediated through direct physical interaction between the helicase and its rG4 substrate. Our findings unveil a previously unknown role for non-canonical structures in governing 5-UTR translation and suggest that the interaction of helicases with rG4s could be considered as a target for future therapeutic intervention.

genomics↗