Project description:Transcription and replication conflict (TRC) are one of the main driving forces for genome instability. Yet, TRC rarely been discussed without the context of DNA:RNA entanglement, rending the role of transcription in other TRC unclear . In neural stem and progenitor cells, genes encode protein regulating neuron adhesion are hotspots for recurrent DNA break clusters (RDC). While RDC-containing genes are all actively transcribed, most RDC lack DNA:RNA entanglement. We demonstrated that, through controlled gain and loss of function genetic approaches, transcription activity is essential while not sufficient to induce RDC formation. In combination of a deep neural network and single-nucleotide resolution DNA break mapping approaches, we found RDC break densities mirror the replication fork dynamics. We demonstrated that, for the first time that, head-on TRC results in higher DNA break density than its co-direction counterparts. In summary, our results revealed that transcription has a higher-level regulatory role that has to be coordinated with DNA replication.
Project description:Recurrent DNA break clusters (RDCs) are replication and transcription collision hotspots. Through high-resolution replication sequencing and a capture-ligation assay in mouse neural progenitor cells experiencing replication stress, we unraveled the replication fork architecture dictating RDC location and orientation. Most RDC occurs at the replication forks traversing timing transition regions (TTRs), where sparse replication origins connect unidirectional forks. Leftward-moving forks generate telomere-connected DNA double-strand breaks (DSB) while rightward-moving forks lead to centromere-connected DSBs. Strand-specific mapping for DNA-bounded RNA revealed transient DNA:RNA hybrids present at a higher density in RDC than in other actively transcribed long genes. In addition, mapping nascent RNA and RNA polymerase activity revealed that head-to-head interactions between replication and transcription machinery slow down DNA replication, resulting in 60% DSB contribution to the head-on as compared to 60% for co-directional . Our findings revealed TTR as a novel fragile class and highlighted how the linear interaction between transcription and replication impacts genome stability.
Project description:Fused-in-sarcoma (FUS) encodes an RNA-binding protein with diverse roles in transcriptional activation and RNA splicing. While oncogenic fusions of FUS and transcription factor DNA-binding domains are associated with soft tissue sarcomas, dominant mutations in FUS cause amyotrophic lateral sclerosis (ALS). FUS has also been implicated in genome maintenance. However, the underlying mechanisms are unknown.
Here, we applied gene editing, functional reconstitution and integrated proteomic and transcriptomics to illuminate roles for FUS in DNA replication and repair. Consistent with a supportive role in DNA double-strand break (DSB) repair FUS deficient cells exhibited subtle alterations in the recruitment and retention of DSB-associated factors, including 53BP1 and BRCA1. FUS-/- cells also exhibited reduced proliferative potential that correlated with reduced replication fork speed, diminished loading of pre-replication complexes, enhanced micronucleus formation, and attenuated expression and splicing of S-phase associated genes. Finally, FUS-deficient cells exhibited genome-wide alterations in DNA replication timing that were reversed upon reeexpression of FUS cDNA. FUS-dependent replication domains were enriched in transcriptionally active chromatin and FUS was required for the timely replication of transcriptionally active DNA. These findings suggest that alterations DNA replication kinetics and programming contribute to genome instability and functional defects in FUS deficient cells.
Project description:BRCA1 functions in multiple biological processes, including double-strand break repair, replication stress suppression, transcriptional regulation, and chromatin reorganization. While non-malignant cells carrying cancer-predisposing BRCA1 mutations exhibit increased genomic instability, it remains unclear whether BRCA1 haploinsufficiency affects transcription and chromatin dynamics. Here we show that primary mammary epithelial cells from women with BRCA1 mutations (BRCA1mut/+) display significant loss of H3K27ac-associated super-enhancers.
Project description:We previously demonstrated that inactivation of the replication checkpoint via a mec1 mutation led to chromosome breakage at replication forks initiated from virtually all origins of replication, after transient exposure to hydroxyurea (HU), an inhibitor of ribonucleotide reductase. Furthermore, we have shown that chromosomes break at replication forks that have suffered single-stranded DNA (ssDNA) formation. Here we sought to determine whether all replication forks containing ssDNA gaps have equal probability of producing double strand breaks (DSBs) when cells attempt to recover from HU exposure. We devised a new methodology, Break-Seq, that combines our previously described DSB labeling with NextGen sequencing to map chromosome breaks with improved sensitivity and resolution. We show that DSBs preferentially occur at genes transcriptionally induced by HU. Notably, different subsets of the HU-induced genes produced DSBs in MEC1 and mec1 cells as replication forks traversed greater distance in MEC1 cells than in mec1 cells during the recovery from HU. Specifically, while MEC1 cells exhibited chromosome breakage at stress-response transcription factors, mec1 cells predominantly suffered chromosome breakage at transporter genes, many of which are the substrates of the said transcription factors. We propose that HU-induced chromosome fragility arises at higher frequency near HU-induced genes as a result of destabilized replication forks encountering transcription factor binding and/or the act of transcription. Our model provides an explanation for a long-standing problem in chromosome biology: why different replication inhibitors produce different spectra of chromosome breakage? We propose that different inhibitors elicit different transcription responses as well as destabilize replication forks, and, when the two processes collide, ssDNA at the replication fork suffers further strand breakage, causing DSBs.
Project description:We previously demonstrated that inactivation of the replication checkpoint via a mec1 mutation led to chromosome breakage at replication forks initiated from virtually all origins of replication, after transient exposure to hydroxyurea (HU), an inhibitor of ribonucleotide reductase. Furthermore, we have shown that chromosomes break at replication forks that have suffered single-stranded DNA (ssDNA) formation. Here we sought to determine whether all replication forks containing ssDNA gaps have equal probability of producing double strand breaks (DSBs) when cells attempt to recover from HU exposure. We devised a new methodology, Break-Seq, that combines our previously described DSB labeling with NextGen sequencing to map chromosome breaks with improved sensitivity and resolution. We show that DSBs preferentially occur at genes transcriptionally induced by HU. Notably, different subsets of the HU-induced genes produced DSBs in MEC1 and mec1 cells as replication forks traversed greater distance in MEC1 cells than in mec1 cells during the recovery from HU. Specifically, while MEC1 cells exhibited chromosome breakage at stress-response transcription factors, mec1 cells predominantly suffered chromosome breakage at transporter genes, many of which are the substrates of the said transcription factors. We propose that HU-induced chromosome fragility arises at higher frequency near HU-induced genes as a result of destabilized replication forks encountering transcription factor binding and/or the act of transcription. Our model provides an explanation for a long-standing problem in chromosome biology: why different replication inhibitors produce different spectra of chromosome breakage? We propose that different inhibitors elicit different transcription responses as well as destabilize replication forks, and, when the two processes collide, ssDNA at the replication fork suffers further strand breakage, causing DSBs.
Project description:Replication of the eukaryotic genome occurs in the context of chromatin, a nucleoprotein packaging state consisting of repeating nucleosomes. Chromatin is commonly thought to carry epigenetic information from one generation to the next, although it is unclear how such information survives the disruptions of nucleosomal architecture that occur during genomic replication. Here, we sought to directly measure a key aspect of chromatin structure dynamics during replication â how rapidly nucleosome positions are established on the newly-replicated daughter genomes. By isolating newly-synthesized DNA marked with the nucleotide analogue EdU, we characterize nucleosome positions on both daughter genomes of budding yeast during a time course of chromatin maturation. We find that nucleosomes rapidly adopt their mid log positions at highly-transcribed genes, and that this process was impaired upon treatment with the transcription inhibitor thiolutin, consistent with a role for transcription in positioning nucleosomes in vivo. Additionally, experiments in the Hir1Î background reveal a role for HIR in nucleosome spacing. Using strand-specific EdU libraries, we characterize nucleosome positions on the leading and lagging strand daughter genomes, uncovering differences in chromatin maturation dynamics between the two daughter genomes at hundreds of genes. Our data define the maturation dynamics of newly-replicated chromatin, and support a role for transcription in sculpting the chromatin template. We have mapped changes in nucleosome positions on newly replicated DNA in a timecourse after genome replication. We have used Micrococcal Nuclease footprinting of cross linked chromatin to determine nucleosome positions and EdU (ethylene deoxy uridine) to mark nascent DNA strands. EdU incorporated into nascent DNA strands was biotinylated with Click chemistry and nascent DNA strand fragments were subsequently isolated using Streptavidin coated magnetic beads.