Tetrahymena Meiotic Nuclear Reorganization Is Induced by a Checkpoint Kinase–dependent Response to DNA Damage

In the ciliate Tetrahymena, meiotic micronuclei (MICs) undergo extreme elongation, and meiotic pairing and recombination take place within these elongated nuclei (the “crescents”). We have previously shown that elongation does not occur in the absence of Spo11p-induced DNA double-strand breaks (DSBs). Here we show that elongation is restored in spo11Δ mutants by various DNA-damaging agents including ones that may not cause DSBs to a notable extent. MIC elongation following Spo11p-induced DSBs or artificially induced DNA lesions is probably a DNA-damage response mediated by a phosphokinase signal transduction pathway, since it is suppressed by the ATM/ATR kinase inhibitors caffeine and wortmannin and by knocking out Tetrahymena's ATR orthologue. MIC elongation occurs concomitantly with the movement of centromeres away from the telomeric pole of the MIC. This DNA damage–dependent reorganization of the MIC helps to arrange homologous chromosomes alongside each other but is not sufficient for exact pairing. Thus, Spo11p contributes to bivalent formation in two ways: by creating a favorable spatial disposition of homologues and by stabilizing pairing by crossovers. The polarized chromosome orientation inside the crescent resembles the conserved meiotic bouquet, and crescent and bouquet also share the putative function of aiding meiotic pairing. However, they are regulated differently because in Tetrahymena, DSBs are required for entering rather than exiting this stage.

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Focused Ion Microbeam Irradiation Induces Clustering of DNA Double-Strand Breaks in Heterochromatin Visualized by Nanoscale-Resolution Electron Microscopy

International Journal of Molecular Sciences ◽

10.3390/ijms22147638 ◽

2021 ◽

Vol 22 (14) ◽

pp. 7638

Author(s):

Yvonne Lorat ◽

Judith Reindl ◽

Anna Isermann ◽

Christian Rübe ◽

Anna A. Friedl ◽

...

Keyword(s):

Electron Microscopy ◽

Dna Damage ◽

Spatial Clustering ◽

Dna Lesions ◽

Double Strand Breaks ◽

Stimulated Emission ◽

Nuclear Chromatin ◽

Carbon Ions ◽

Dna Double Strand Breaks ◽

Strand Breaks

Background: Charged-particle radiotherapy is an emerging treatment modality for radioresistant tumors. The enhanced effectiveness of high-energy particles (such as heavy ions) has been related to the spatial clustering of DNA lesions due to highly localized energy deposition. Here, DNA damage patterns induced by single and multiple carbon ions were analyzed in the nuclear chromatin environment by different high-resolution microscopy approaches. Material and Methods: Using the heavy-ion microbeam SNAKE, fibroblast monolayers were irradiated with defined numbers of carbon ions (1/10/100 ions per pulse, ipp) focused to micrometer-sized stripes or spots. Radiation-induced lesions were visualized as DNA damage foci (γH2AX, 53BP1) by conventional fluorescence and stimulated emission depletion (STED) microscopy. At micro- and nanoscale level, DNA double-strand breaks (DSBs) were visualized within their chromatin context by labeling the Ku heterodimer. Single and clustered pKu70-labeled DSBs were quantified in euchromatic and heterochromatic regions at 0.1 h, 5 h and 24 h post-IR by transmission electron microscopy (TEM). Results: Increasing numbers of carbon ions per beam spot enhanced spatial clustering of DNA lesions and increased damage complexity with two or more DSBs in close proximity. This effect was detectable in euchromatin, but was much more pronounced in heterochromatin. Analyzing the dynamics of damage processing, our findings indicate that euchromatic DSBs were processed efficiently and repaired in a timely manner. In heterochromatin, by contrast, the number of clustered DSBs continuously increased further over the first hours following IR exposure, indicating the challenging task for the cell to process highly clustered DSBs appropriately. Conclusion: Increasing numbers of carbon ions applied to sub-nuclear chromatin regions enhanced the spatial clustering of DSBs and increased damage complexity, this being more pronounced in heterochromatic regions. Inefficient processing of clustered DSBs may explain the enhanced therapeutic efficacy of particle-based radiotherapy in cancer treatment.

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Recent advances in the nucleolar responses to DNA double-strand breaks

Nucleic Acids Research ◽

10.1093/nar/gkaa713 ◽

2020 ◽

Vol 48 (17) ◽

pp. 9449-9461

Author(s):

Lea Milling Korsholm ◽

Zita Gál ◽

Blanca Nieto ◽

Oliver Quevedo ◽

Stavroula Boukoura ◽

...

Keyword(s):

Dna Damage ◽

Dna Repair ◽

Dna Damage Response ◽

Ribosomal Dna ◽

Repetitive Sequences ◽

Dna Lesions ◽

Double Strand Breaks ◽

Dna Double Strand Breaks ◽

Strand Breaks ◽

Damage Response

Abstract DNA damage poses a serious threat to human health and cells therefore continuously monitor and repair DNA lesions across the genome. Ribosomal DNA is a genomic domain that represents a particular challenge due to repetitive sequences, high transcriptional activity and its localization in the nucleolus, where the accessibility of DNA repair factors is limited. Recent discoveries have significantly extended our understanding of how cells respond to DNA double-strand breaks (DSBs) in the nucleolus, and new kinases and multiple down-stream targets have been identified. Restructuring of the nucleolus can occur as a consequence of DSBs and new data point to an active regulation of this process, challenging previous views. Furthermore, new insights into coordination of cell cycle phases and ribosomal DNA repair argue against existing concepts. In addition, the importance of nucleolar-DNA damage response (n-DDR) mechanisms for maintenance of genome stability and the potential of such factors as anti-cancer targets is becoming apparent. This review will provide a detailed discussion of recent findings and their implications for our understanding of the n-DDR. The n-DDR shares features with the DNA damage response (DDR) elsewhere in the genome but is also emerging as an independent response unique to ribosomal DNA and the nucleolus.

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SETD2 is required for DNA double-strand break repair and activation of the p53-mediated checkpoint

eLife ◽

10.7554/elife.02482 ◽

2014 ◽

Vol 3 ◽

Cited By ~ 121

Author(s):

Sílvia Carvalho ◽

Alexandra C Vítor ◽

Sreerama C Sridhara ◽

Filipa B Martins ◽

Ana C Raposo ◽

...

Keyword(s):

Dna Damage ◽

Strand Break ◽

Dna Lesions ◽

Alternative Mechanism ◽

Dna Double Strand Breaks ◽

Cell Renal Cell Carcinoma ◽

Strand Breaks ◽

Dna Damage Signaling ◽

Dna Double Strand Break ◽

Recombination Repair

Histone modifications establish the chromatin states that coordinate the DNA damage response. In this study, we show that SETD2, the enzyme that trimethylates histone H3 lysine 36 (H3K36me3), is required for ATM activation upon DNA double-strand breaks (DSBs). Moreover, we find that SETD2 is necessary for homologous recombination repair of DSBs by promoting the formation of RAD51 presynaptic filaments. In agreement, SETD2-mutant clear cell renal cell carcinoma (ccRCC) cells displayed impaired DNA damage signaling. However, despite the persistence of DNA lesions, SETD2-deficient cells failed to activate p53, a master guardian of the genome rarely mutated in ccRCC and showed decreased cell survival after DNA damage. We propose that this novel SETD2-dependent role provides a chromatin bookmarking instrument that facilitates signaling and repair of DSBs. In ccRCC, loss of SETD2 may afford an alternative mechanism for the inactivation of the p53-mediated checkpoint without the need for additional genetic mutations in TP53.

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Poly(ADP-ribosyl)ation mediates early phase histone eviction at DNA lesions

Nucleic Acids Research ◽

10.1093/nar/gkaa022 ◽

2020 ◽

Vol 48 (6) ◽

pp. 3001-3013 ◽

Cited By ~ 4

Author(s):

Guang Yang ◽

Yibin Chen ◽

Jiaxue Wu ◽

Shih-Hsun Chen ◽

Xiuhua Liu ◽

...

Keyword(s):

Dna Damage ◽

Molecular Mechanism ◽

Parp Inhibitor ◽

Repair Process ◽

Dna Lesions ◽

Histone Chaperones ◽

Dna Double Strand Breaks ◽

Strand Breaks ◽

Dna Lesion ◽

Damage Repair

Abstract Nucleosomal histones are barriers to the DNA repair process particularly at DNA double-strand breaks (DSBs). However, the molecular mechanism by which these histone barriers are removed from the sites of DNA damage remains elusive. Here, we have generated a single specific inducible DSB in the cells and systematically examined the histone removal process at the DNA lesion. We found that histone removal occurred immediately following DNA damage and could extend up to a range of few kilobases from the lesion. To examine the molecular mechanism underlying DNA damage-induced histone removal, we screened histone modifications and found that histone ADP-ribosylation was associated with histone removal at DNA lesions. PARP inhibitor treatment suppressed the immediate histone eviction at DNA lesions. Moreover, we examined histone chaperones and found that the FACT complex recognized ADP-ribosylated histones and mediated the removal of histones in response to DNA damage. Taken together, our results reveal a pathway that regulates early histone barrier removal at DNA lesions. It may also explain the mechanism by which PARP inhibitor regulates early DNA damage repair.

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DDB1 Maintains Genome Integrity through Regulation of Cdt1

Molecular and Cellular Biology ◽

10.1128/mcb.00819-06 ◽

2006 ◽

Vol 26 (21) ◽

pp. 7977-7990 ◽

Cited By ~ 59

Author(s):

Courtney A. Lovejoy ◽

Kimberli Lock ◽

Ashwini Yenamandra ◽

David Cortez

Keyword(s):

Dna Damage ◽

Genome Stability ◽

Genome Instability ◽

Excision Repair ◽

Dna Lesions ◽

Cell Cycle Checkpoints ◽

Dna Double Strand Breaks ◽

Genome Maintenance ◽

Strand Breaks ◽

Ubiquitin Ligase Complex

ABSTRACT DDB1, a component of a Cul4A ubiquitin ligase complex, promotes nucleotide excision repair (NER) and regulates DNA replication. We have investigated the role of human DDB1 in maintaining genome stability. DDB1-depleted cells accumulate DNA double-strand breaks in widely dispersed regions throughout the genome and have activated ATM and ATR cell cycle checkpoints. Depletion of Cul4A yields similar phenotypes, indicating that an E3 ligase function of DDB1 is important for genome maintenance. In contrast, depletion of DDB2, XPA, or XPC does not cause activation of DNA damage checkpoints, indicating that defects in NER are not involved. One substrate of DDB1-Cul4A that is crucial for preventing genome instability is Cdt1. DDB1-depleted cells exhibit increased levels of Cdt1 protein and rereplication, despite containing other Cdt1 regulatory mechanisms. The rereplication, accumulation of DNA damage, and activation of checkpoint responses in DDB1-depleted cells require entry into S phase and are partially, but not completely, suppressed by codepletion of Cdt1. Therefore, DDB1 prevents DNA lesions from accumulating in replicating human cells, in part by regulating Cdt1 degradation.

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A simple microscopy setup for visualizing cellular responses to DNA damage at particle accelerator facilities

Scientific Reports ◽

10.1038/s41598-021-92950-1 ◽

2021 ◽

Vol 11 (1) ◽

Author(s):

Haibin Qian ◽

Ron A. Hoebe ◽

Michel R. Faas ◽

Marc Jan van Goethem ◽

Emiel R. van der Graaf ◽

...

Keyword(s):

Dna Damage ◽

Cellular Responses ◽

Particle Beam ◽

Early Response ◽

Dna Lesions ◽

Particle Accelerator ◽

Dna Double Strand Breaks ◽

Key Factors ◽

Cancer Treatments ◽

Strand Breaks

AbstractCellular responses to DNA double-strand breaks (DSBs) not only promote genomic integrity in healthy tissues, but also largely determine the efficacy of many DNA-damaging cancer treatments, including X-ray and particle therapies. A growing body of evidence suggests that activation of the mechanisms that detect, signal and repair DSBs may depend on the complexity of the initiating DNA lesions. Studies focusing on this, as well as on many other radiobiological questions, require reliable methods to induce DSBs of varying complexity, and to visualize the ensuing cellular responses. Accelerated particles of different energies and masses are exceptionally well suited for this task, due to the nature of their physical interactions with the intracellular environment, but visualizing cellular responses to particle-induced damage - especially in their early stages - at particle accelerator facilities, remains challenging. Here we describe a straightforward approach for real-time imaging of early response to particle-induced DNA damage. We rely on a transportable setup with an inverted fluorescence confocal microscope, tilted at a small angle relative to the particle beam, such that cells can be irradiated and imaged without any microscope or beamline modifications. Using this setup, we image and analyze the accumulation of fluorescently-tagged MDC1, RNF168 and 53BP1—key factors involved in DSB signalling—at DNA lesions induced by 254 MeV α-particles. Our results provide a demonstration of technical feasibility and reveal asynchronous initiation of accumulation of these proteins at different individual DSBs.

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Visualization of complex DNA damage along accelerated ions tracks

EPJ Web of Conferences ◽

10.1051/epjconf/201817706002 ◽

2018 ◽

Vol 177 ◽

pp. 06002

Author(s):

Elena Kulikova ◽

Alla Boreyko ◽

Tatiana Bulanova ◽

Lucie Ježková ◽

Mariia Zadneprianetc ◽

...

Keyword(s):

Dna Damage ◽

Human Fibroblasts ◽

Dna Lesions ◽

3D Analysis ◽

Dna Double Strand Breaks ◽

Base Damage ◽

Strand Breaks ◽

Single Strand Breaks ◽

Dna Dsbs ◽

Γ Rays

The most deleterious DNA lesions induced by ionizing radiation are clustered DNA double-strand breaks (DSB). Clustered or complex DNA damage is a combination of a few simple lesions (single-strand breaks, base damage etc.) within one or two DNA helix turns. It is known that yield of complex DNA lesions increases with increasing linear energy transfer (LET) of radiation. For investigation of the induction and repair of complex DNA lesions, human fibroblasts were irradiated with high-LET 15N ions (LET = 183.3 keV/μm, E = 13MeV/n) and low-LET 60Co γ-rays (LET ≈ 0.3 keV/μm) radiation. DNA DSBs (γH2AX and 53BP1) and base damage (OGG1) markers were visualized by immunofluorecence staining and high-resolution microscopy. The obtained results showed slower repair kinetics of induced DSBs in cells irradiated with accelerated ions compared to 60Co γ-rays, indicating induction of more complex DNA damage. Confirming previous assumptions, detailed 3D analysis of γH2AX/53BP1 foci in 15N ions tracks revealed more complicated structure of the foci in contrast to γ-rays. It was shown that proteins 53BP1 and OGG1 involved in repair of DNA DSBs and modified bases, respectively, were colocalized in tracks of 15N ions and thus represented clustered DNA DSBs.

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DNA damage interactions on both nanometer and micrometer scale determine overall cellular damage

Scientific Reports ◽

10.1038/s41598-018-34323-9 ◽

2018 ◽

Vol 8 (1) ◽

Cited By ~ 16

Author(s):

Thomas Friedrich ◽

Katarina Ilicic ◽

Christoph Greubel ◽

Stefanie Girst ◽

Judith Reindl ◽

...

Keyword(s):

Dna Damage ◽

Cellular Level ◽

Dna Lesions ◽

Double Strand Breaks ◽

Cellular Damage ◽

Biophysical Model ◽

Dna Double Strand Breaks ◽

Strand Breaks ◽

Dna Lesion ◽

Micrometer Scale

Abstract DNA double strand breaks (DSB) play a pivotal role for cellular damage, which is a hazard encountered in toxicology and radiation protection, but also exploited e.g. in eradicating tumors in radiation therapy. It is still debated whether and in how far clustering of such DNA lesions leads to an enhanced severity of induced damage. Here we investigate - using focused spots of ionizing radiation as damaging agent - the spatial extension of DNA lesion patterns causing cell inactivation. We find that clustering of DNA damage on both the nm and µm scale leads to enhanced inactivation compared to more homogeneous lesion distributions. A biophysical model interprets these observations in terms of enhanced DSB production and DSB interaction, respectively. We decompose the overall effects quantitatively into contributions from these lesion formation processes, concluding that both processes coexist and need to be considered for determining the resulting damage on the cellular level.

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Clustered DNA Double-Strand Breaks: Biological Effects and Relevance to Cancer Radiotherapy

Genes ◽

10.3390/genes11010099 ◽

2020 ◽

Vol 11 (1) ◽

pp. 99 ◽

Cited By ~ 14

Author(s):

Jac A. Nickoloff ◽

Neelam Sharma ◽

Lynn Taylor

Keyword(s):

Dna Damage ◽

Dna Lesions ◽

Double Strand Breaks ◽

Single Strand ◽

Dna Double Strand Breaks ◽

Strand Breaks ◽

High Let Radiation ◽

High Let ◽

Radiation Induced ◽

Clustered Dna Damage

Cells manage to survive, thrive, and divide with high accuracy despite the constant threat of DNA damage. Cells have evolved with several systems that efficiently repair spontaneous, isolated DNA lesions with a high degree of accuracy. Ionizing radiation and a few radiomimetic chemicals can produce clustered DNA damage comprising complex arrangements of single-strand damage and DNA double-strand breaks (DSBs). There is substantial evidence that clustered DNA damage is more mutagenic and cytotoxic than isolated damage. Radiation-induced clustered DNA damage has proven difficult to study because the spectrum of induced lesions is very complex, and lesions are randomly distributed throughout the genome. Nonetheless, it is fairly well-established that radiation-induced clustered DNA damage, including non-DSB and DSB clustered lesions, are poorly repaired or fail to repair, accounting for the greater mutagenic and cytotoxic effects of clustered lesions compared to isolated lesions. High linear energy transfer (LET) charged particle radiation is more cytotoxic per unit dose than low LET radiation because high LET radiation produces more clustered DNA damage. Studies with I-SceI nuclease demonstrate that nuclease-induced DSB clusters are also cytotoxic, indicating that this cytotoxicity is independent of radiogenic lesions, including single-strand lesions and chemically “dirty” DSB ends. The poor repair of clustered DSBs at least in part reflects inhibition of canonical NHEJ by short DNA fragments. This shifts repair toward HR and perhaps alternative NHEJ, and can result in chromothripsis-mediated genome instability or cell death. These principals are important for cancer treatment by low and high LET radiation.

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PARP1 exhibits enhanced association and catalytic efficiency with γH2A.X-nucleosome

Nature Communications ◽

10.1038/s41467-019-13641-0 ◽

2019 ◽

Vol 10 (1) ◽

Cited By ~ 2

Author(s):

Deepti Sharma ◽

Louis De Falco ◽

Sivaraman Padavattan ◽

Chang Rao ◽

Susana Geifman-Shochat ◽

...

Keyword(s):

Dna Damage ◽

Mutational Analysis ◽

Catalytic Efficiency ◽

Double Strand Breaks ◽

Genomic Integrity ◽

Dna Double Strand Breaks ◽

Strand Breaks ◽

Nucleosome Core ◽

Epigenetic Marker ◽

Kinetics Of

AbstractThe poly(ADP-ribose) polymerase, PARP1, plays a key role in maintaining genomic integrity by detecting DNA damage and mediating repair. γH2A.X is the primary histone marker for DNA double-strand breaks and PARP1 localizes to H2A.X-enriched chromatin damage sites, but the basis for this association is not clear. We characterize the kinetics of PARP1 binding to a variety of nucleosomes harbouring DNA double-strand breaks, which reveal that PARP1 associates faster with (γ)H2A.X- versus H2A-nucleosomes, resulting in a higher affinity for the former, which is maximal for γH2A.X-nucleosome that is also the activator eliciting the greatest poly-ADP-ribosylation catalytic efficiency. The enhanced activities with γH2A.X-nucleosome coincide with increased accessibility of the DNA termini resulting from the H2A.X-Ser139 phosphorylation. Indeed, H2A- and (γ)H2A.X-nucleosomes have distinct stability characteristics, which are rationalized by mutational analysis and (γ)H2A.X-nucleosome core crystal structures. This suggests that the γH2A.X epigenetic marker directly facilitates DNA repair by stabilizing PARP1 association and promoting catalysis.

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