scholarly journals Unscheduled origin building in S-phase upon tight CDK1 inhibition suppresses CFS instability

2020 ◽  
Author(s):  
Olivier Brison ◽  
Stefano Gnan ◽  
Dana Azar ◽  
Mélanie Schmidt ◽  
Stéphane Koundrioukoff ◽  
...  
Keyword(s):  
Chromosome Segregation ◽  
Genome Stability ◽  
Chromosome Breakage ◽  
S Phase ◽  
Fragile Sites ◽  
Human Cells ◽  
Genome Integrity ◽  
Checkpoint Activation ◽  
Chromosome Domains ◽  
Molecular Combing

SummaryGenome integrity requires replication to be completed before chromosome segregation. This coordination essentially relies on replication-dependent activation of a dedicated checkpoint that inhibits CDK1, delaying mitotic onset. Under-replication of Common Fragile Sites (CFSs) however escapes surveillance, which triggers chromosome breakage. Using human cells, we asked here whether such leakage results from insufficient CDK1 inhibition under modest stresses used to destabilize CFSs. We found that tight CDK1 inhibition suppresses CFS instability. Repli-Seq and molecular combing analyses consistently showed a burst of replication initiations in mid S phase across large origin-poor domains shaped by transcription, including CFSs. Strikingly, CDC6 or CDT1 depletion or CDC7-DBF4 inhibition during the S phase prevented both extra-initiations and CFS rescue, showing that CDK1 inhibition promotes targeted and mistimed building of functional extra-origins. In addition to delay mitotic onset, checkpoint activation therefore advances replication completion of chromosome domains at risk of under-replication, two complementary roles preserving genome stability.

scholarly journals The RAD51 recombinase protects mitotic chromatin in human cells

2021 ◽  
Vol 12 (1) ◽  
Author(s):  
Isabel E. Wassing ◽  
Emily Graham ◽  
Xanita Saayman ◽  
Lucia Rampazzo ◽  
Christine Ralf ◽  
...  
Keyword(s):  
Chromosome Segregation ◽  
Genome Stability ◽  
Spindle Assembly Checkpoint ◽  
De Novo ◽  
Genomic Stability ◽  
Human Cells ◽  
Genome Integrity ◽  
Chromosomal Replication ◽  
Anaphase Onset ◽  
Mitotic Chromatin

AbstractThe RAD51 recombinase plays critical roles in safeguarding genome integrity, which is fundamentally important for all living cells. While interphase functions of RAD51 in maintaining genome stability are well-characterised, its role in mitosis remains contentious. In this study, we show that RAD51 protects under-replicated DNA in mitotic human cells and, in this way, promotes mitotic DNA synthesis (MiDAS) and successful chromosome segregation. In cells experiencing mild replication stress, MiDAS was detected irrespective of mitotically generated DNA damage. MiDAS broadly required de novo RAD51 recruitment to single-stranded DNA, which was supported by the phosphorylation of RAD51 by the key mitotic regulator Polo-like kinase 1. Importantly, acute inhibition of MiDAS delayed anaphase onset and induced centromere fragility, suggesting a mechanism that prevents the satisfaction of the spindle assembly checkpoint while chromosomal replication remains incomplete. This study hence identifies an unexpected function of RAD51 in promoting genomic stability in mitosis.

scholarly journals Heterochromatin: Guardian of the Genome

2018 ◽  
Vol 34 (1) ◽  
pp. 265-288 ◽  
Author(s):  
Aniek Janssen ◽  
Serafin U. Colmenares ◽  
Gary H. Karpen
Keyword(s):  
Chromosome Segregation ◽  
Genome Stability ◽  
Constitutive Heterochromatin ◽  
Repetitive Sequences ◽  
Genome Integrity ◽  
Chromatin Domain ◽  
Cellular Processes ◽  
Eukaryotic Nucleus ◽  
And Function ◽  
Heterochromatin Structure

Constitutive heterochromatin is a major component of the eukaryotic nucleus and is essential for the maintenance of genome stability. Highly concentrated at pericentromeric and telomeric domains, heterochromatin is riddled with repetitive sequences and has evolved specific ways to compartmentalize, silence, and repair repeats. The delicate balance between heterochromatin epigenetic maintenance and cellular processes such as mitosis and DNA repair and replication reveals a highly dynamic and plastic chromatin domain that can be perturbed by multiple mechanisms, with far-reaching consequences for genome integrity. Indeed, heterochromatin dysfunction provokes genetic turmoil by inducing aberrant repeat repair, chromosome segregation errors, transposon activation, and replication stress and is strongly implicated in aging and tumorigenesis. Here, we summarize the general principles of heterochromatin structure and function, discuss the importance of its maintenance for genome integrity, and propose that more comprehensive analyses of heterochromatin roles in tumorigenesis will be integral to future innovations in cancer treatment.

scholarly journals DNA replication and spindle checkpoints cooperate during S phase to delay mitosis and preserve genome integrity

2014 ◽  
Vol 204 (2) ◽  
pp. 165-175 ◽  
Author(s):  
Maria M. Magiera ◽  
Elisabeth Gueydon ◽  
Etienne Schwob
Keyword(s):  
Dna Replication ◽  
Chromosome Segregation ◽  
Replication Stress ◽  
S Phase ◽  
Genome Integrity ◽  
Replication Forks ◽  
Mitotic Entry ◽  
Transient Activation ◽  
Spindle Checkpoints ◽  
Spindle Assembly Checkpoints

Deoxyribonucleic acid (DNA) replication and chromosome segregation must occur in ordered sequence to maintain genome integrity during cell proliferation. Checkpoint mechanisms delay mitosis when DNA is damaged or upon replication stress, but little is known on the coupling of S and M phases in unperturbed conditions. To address this issue, we postponed replication onset in budding yeast so that DNA synthesis is still underway when cells should enter mitosis. This delayed mitotic entry and progression by transient activation of the S phase, G2/M, and spindle assembly checkpoints. Disabling both Mec1/ATR- and Mad2-dependent controls caused lethality in cells with deferred S phase, accompanied by Rad52 foci and chromosome missegregation. Thus, in contrast to acute replication stress that triggers a sustained Mec1/ATR response, multiple pathways cooperate to restrain mitosis transiently when replication forks progress unhindered. We suggest that these surveillance mechanisms arose when both S and M phases were coincidently set into motion by a unique ancestral cyclin–Cdk1 complex.

scholarly journals The yeast core spliceosome maintains genome integrity through R-loop prevention and α-tubulin expression

2018 ◽  
Author(s):  
Annie S. Tam ◽  
Veena Mathew ◽  
Tianna S. Sihota ◽  
Anni Zhang ◽  
Peter C. Stirling
Keyword(s):  
Gene Expression ◽  
Dna Replication ◽  
Chromosome Segregation ◽  
Genome Stability ◽  
Spindle Assembly Checkpoint ◽  
Genome Instability ◽  
Genome Integrity ◽  
Genome Maintenance ◽  
Maintenance Factors ◽  
Spindle Assembly Checkpoint Protein

To achieve genome stability cells must coordinate the action of various DNA transactions including DNA replication, repair, transcription and chromosome segregation. How transcription and RNA processing enable genome stability is only partly understood. Two predominant models have emerged: one involving changes in gene expression that perturb other genome maintenance factors, and another in which genotoxic DNA:RNA hybrids, called R-loops, impair DNA replication. Here we characterize genome instability phenotypes in a panel yeast splicing factor mutants and find that mitotic defects, and in some cases R-loop accumulation, are causes of genome instability. Genome instability in splicing mutants is exacerbated by loss of the spindle-assembly checkpoint protein Mad1. Moreover, removal of the intron from the α-tubulin gene TUB1 restores genome integrity. Thus, while R-loops contribute in some settings, defects in yeast splicing predominantly lead to genome instability through effects on gene expression.

scholarly journals Human DNA Polymerase η Is Required for Common Fragile Site Stability during Unperturbed DNA Replication

2009 ◽  
Vol 29 (12) ◽  
pp. 3344-3354 ◽  
Author(s):  
Laurie Rey ◽  
Julia M. Sidorova ◽  
Nadine Puget ◽  
François Boudsocq ◽  
Denis S. F. Biard ◽  
...  
Keyword(s):  
Dna Damage ◽  
Dna Polymerase ◽  
Genome Stability ◽  
Fragile Site ◽  
S Phase ◽  
Human Cells ◽  
Common Fragile Site ◽  
Exogenous Dna ◽  
Human Dna

ABSTRACT Human DNA polymerase η (Pol η) modulates susceptibility to skin cancer by promoting translesion DNA synthesis (TLS) past sunlight-induced cyclobutane pyrimidine dimers. Despite its well-established role in TLS synthesis, the role of Pol η in maintaining genome stability in the absence of external DNA damage has not been well explored. We show here that short hairpin RNA-mediated depletion of Pol η from undamaged human cells affects cell cycle progression and the rate of cell proliferation and results in increased spontaneous chromosome breaks and common fragile site expression with the activation of ATM-mediated DNA damage checkpoint signaling. These phenotypes were also observed in association with modified replication factory dynamics during S phase. In contrast to that seen in Pol η-depleted cells, none of these cellular or karyotypic defects were observed in cells depleted for Pol ι, the closest relative of Pol η. Our results identify a new role for Pol η in maintaining genomic stability during unperturbed S phase and challenge the idea that the sole functional role of Pol η in human cells is in TLS DNA damage tolerance and/or repair pathways following exogenous DNA damage.

scholarly journals Palindromes in DNA—A Risk for Genome Stability and Implications in Cancer

2021 ◽  
Vol 22 (6) ◽  
pp. 2840
Author(s):  
Marina Svetec Miklenić ◽  
Ivan Krešimir Svetec
Keyword(s):  
Human Genome ◽  
Genome Stability ◽  
Molecular Mechanisms ◽  
Genetic Recombination ◽  
Chromosome Breakage ◽  
Fragile Sites ◽  
Cis Acting ◽  
Underlying Mechanisms ◽  
Palindromic Sequences ◽  
Genetic Rearrangements

A palindrome in DNA consists of two closely spaced or adjacent inverted repeats. Certain palindromes have important biological functions as parts of various cis-acting elements and protein binding sites. However, many palindromes are known as fragile sites in the genome, sites prone to chromosome breakage which can lead to various genetic rearrangements or even cell death. The ability of certain palindromes to initiate genetic recombination lies in their ability to form secondary structures in DNA which can cause replication stalling and double-strand breaks. Given their recombinogenic nature, it is not surprising that palindromes in the human genome are involved in genetic rearrangements in cancer cells as well as other known recurrent translocations and deletions associated with certain syndromes in humans. Here, we bring an overview of current understanding and knowledge on molecular mechanisms of palindrome recombinogenicity and discuss possible implications of DNA palindromes in carcinogenesis. Furthermore, we overview the data on known palindromic sequences in the human genome and efforts to estimate their number and distribution, as well as underlying mechanisms of genetic rearrangements specific palindromic sequences cause.

scholarly journals GCNA preserves genome integrity and fertility across species

2019 ◽  
Author(s):  
Varsha Bhargava ◽  
Courtney D. Goldstein ◽  
Logan Russell ◽  
Lin Xu ◽  
Murtaza Ahmed ◽  
...  
Keyword(s):  
Germ Cell ◽  
Chromosome Segregation ◽  
Germ Cells ◽  
Genome Stability ◽  
Replication Stress ◽  
Genome Integrity ◽  
Intrinsically Disordered ◽  
Early Embryos ◽  
The Face ◽  
Protein Crosslinks

SUMMARYThe propagation of species depends on the ability of germ cells to protect their genome in the face of numerous exogenous and endogenous threats. While these cells employ a number of known repair pathways, specialized mechanisms that ensure high-fidelity replication, chromosome segregation, and repair of germ cell genomes remain incompletely understood. Here, we identify Germ Cell Nuclear Acidic Peptidase (GCNA) as a highly conserved regulator of genome stability in flies, worms, zebrafish, and humans. GCNA contains a long acidic intrinsically disordered region (IDR) and a protease-like SprT domain. In addition to chromosomal instability and replication stress, GCNA mutants accumulate DNA-protein crosslinks (DPCs). GCNA acts in parallel with a second SprT domain protein Spartan. Structural analysis reveals that while the SprT domain is needed to limit meiotic and replicative damage, most of GCNA’s function maps to its IDR. This work shows GCNA protects germ cells from various sources of damage, providing novel insights into conserved mechanisms that promote genome integrity across generations.HighlightsGCNA ensures genomic stability in germ cells and early embryos across speciesGCNA limits replication stress and DNA double stranded breaksGCNA restricts DNA-Protein Crosslinks within germ cells and early embryosThe IDR and SprT domains of GCNA govern distinct aspects of genome integrityGraphic Abstract

scholarly journals The Unresolved Problem of DNA Bridging

Genes ◽  
2018 ◽  
Vol 9 (12) ◽  
pp. 623 ◽  
Author(s):  
María Fernández-Casañas ◽  
Kok-Lung Chan
Keyword(s):  
Chromosome Segregation ◽  
Genome Stability ◽  
Genetic Material ◽  
Genome Integrity ◽  
Cellular Division ◽  
Daughter Cells ◽  
Dna Replication And Repair ◽  
A Cell ◽  
Chromosome Separation ◽  
Last Stage

Accurate duplication and transmission of identical genetic information into offspring cells lies at the heart of a cell division cycle. During the last stage of cellular division, namely mitosis, the fully replicated DNA molecules are condensed into X-shaped chromosomes, followed by a chromosome separation process called sister chromatid disjunction. This process allows for the equal partition of genetic material into two newly born daughter cells. However, emerging evidence has shown that faithful chromosome segregation is challenged by the presence of persistent DNA intertwining structures generated during DNA replication and repair, which manifest as so-called ultra-fine DNA bridges (UFBs) during anaphase. Undoubtedly, failure to disentangle DNA linkages poses a severe threat to mitosis and genome integrity. This review will summarize the possible causes of DNA bridges, particularly sister DNA inter-linkage structures, in an attempt to explain how they may be processed and how they influence faithful chromosome segregation and the maintenance of genome stability.

scholarly journals Transcription-dependent regulation of replication dynamics modulates genome stability

2018 ◽  
Author(s):  
Marion Blin ◽  
Benoît Le Tallec ◽  
Viola Naehse ◽  
Mélanie Schmidt ◽  
Gael A. Millot ◽  
...  
Keyword(s):  
Genome Stability ◽  
Chromosomal Rearrangements ◽  
Replication Timing ◽  
Replication Stress ◽  
S Phase ◽  
Fragile Sites ◽  
Replication Initiation ◽  
Replication Gene ◽  
Large Genes ◽  
Dynamics Analyses

Replication stress is a primary threat to genome stability and has been implicated in tumorigenesis1, 2. Common fragile sites (CFSs) are loci hypersensitive to replication stress3 and are hotspots for chromosomal rearrangements in cancers4. CFSs replicate late in S-phase3, are cell-type dependent4–6 and nest within very large genes4, 7–9. The mechanisms responsible for CFS instability are still discussed, notably the relative impact of transcription-replication conflicts7, 8, 10versus their low density in replication initiation events5, 6. Here we address the relationships between transcription, replication, gene size and instability by manipulating the transcription of three endogenous large genes, two in chicken and one in human cells. Remarkably, moderate transcription destabilises large genes whereas high transcription levels alleviate their instability. Replication dynamics analyses showed that transcription quantitatively shapes the replication program of large genes, setting both their initiation profile and their replication timing as well as regulating internal fork velocity. Noticeably, high transcription levels advance the replication time of large genes from late to mid S-phase, which most likely gives cells more time to complete replication before mitotic entry. Transcription can therefore contribute to maintaining the integrity of some difficult-to-replicate loci, challenging the dominant view that it is exclusively a threat to genome stability.

scholarly journals Maternal Smc3 protects the integrity of the zygotic genome through DNA replication and mitosis

Development ◽  
2021 ◽  
Author(s):  
Wei-Ting Yueh ◽  
Vijay Pratap Singh ◽  
Jennifer L. Gerton
Keyword(s):  
Dna Replication ◽  
Chromosome Segregation ◽  
Meiotic Chromosome ◽  
S Phase ◽  
Dna Lesions ◽  
Genome Integrity ◽  
Mammalian Development ◽  
Cell Stage ◽  
Early Embryos ◽  
Zygotic Genome

Aneuploidy is frequently observed in oocytes and early embryos, begging the question of how genome integrity is monitored and preserved during this critical period. SMC3 is a subunit of the cohesin complex that supports genome integrity, but its role in maintaining the genome in this window of mammalian development is unknown. We discovered that although depletion of Smc3 following meiotic S phase in mouse oocytes allowed accurate meiotic chromosome segregation, adult females were infertile. We provide evidence that DNA lesions accumulated following S phase in SMC3-deficient zygotes, followed by mitosis with lagging chromosomes, elongated spindles, micronuclei, and arrest at the 2-cell stage. Remarkably, although centromeric cohesion was defective, the dosage of SMC3 was sufficient to enable embryogenesis in juvenile mutant females. Our findings suggest that despite previous reports of aneuploidy in early embryos, chromosome missegregation in zygotes halts embryogenesis at the 2-cell stage. Smc3 is a maternal gene with essential functions in repair of spontaneous damage associated with DNA replication and subsequent chromosome segregation in zygotes, making cohesin a key protector of the zygotic genome.

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