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Double-strand break repair model

The double-strand break repair (DSBR) model is a foundational mechanism in homologous recombination (HR) that repairs DNA double-strand breaks (DSBs) by using a homologous DNA template to restore genetic information with high fidelity, originally proposed to explain meiotic recombination events such as gene conversion and crossing over in yeast.^[1] In this process, a DSB is enlarged into a gap through resection, generating single-stranded DNA (ssDNA) tails that facilitate strand invasion into the donor duplex, followed by DNA synthesis to copy the missing sequence and resolution of intermediate structures to complete repair.^[2] This model, first articulated by Szostak, Orr-Weaver, Rothstein, and Stahl in 1983, revolutionized understanding of recombination by shifting focus from single-strand nicks to DSBs as the initiating lesion, providing a unified explanation for nonreciprocal gene conversion via gap repair and postmeiotic segregation from heteroduplex DNA at gap edges.^[1] Key steps include: end resection by nucleases like Exo1 and Dna2 to produce 3'-ssDNA overhangs coated with RPA and Rad51 to form a nucleoprotein filament; strand invasion where the Rad51 filament searches for and invades the homologous donor, displacing one strand to form a D-loop; DNA synthesis extending the invading strand using the donor as a template, often by DNA polymerase δ; and resolution through second-end capture, ligation, and either Holliday junction dissolution (non-crossover) or cleavage (crossover products), mediated by proteins such as Rad52, BRCA2, Rad54, and resolvases like Mus81-Eme1.^[2] While initially tied to meiosis, the DSBR pathway operates in mitotic cells to suppress genomic instability, prevent loss of heterozygosity, and support DNA damage tolerance, with defects linked to cancer predisposition syndromes like Fanconi anemia and BRCA-related disorders.^[2] The model's efficiency and accuracy make HR the preferred DSB repair route in S/G2 phases, contrasting with error-prone non-homologous end joining (NHEJ) dominant in G1.^[2]

Fundamentals of Double-Strand Breaks

Definition and Biological Importance

A double-strand break (DSB) is a critical form of DNA damage characterized by a severance in both strands of the DNA double helix at the same or proximate locations, distinguishing it from single-strand breaks (SSBs), which involve only one strand and allow repair using the undamaged complementary strand as a template.^[3]^[4] DSBs disrupt the continuity of the genome, potentially separating chromosomes into fragments if not addressed.^[5] Structurally, DSBs vary in complexity and end configuration: simple DSBs feature clean fractures with minimal surrounding damage, while complex DSBs include clustered lesions such as base modifications or additional breaks nearby, complicating repair; end types include blunt ends (flush, without overhangs) or cohesive ends (with protruding single-stranded sequences that can base-pair).^[5]^[6] These variations influence repair efficiency and fidelity, with blunt ends often proving more challenging to rejoin accurately than cohesive ones.^[7] Biologically, DSBs carry profound importance due to their potential to induce cell death, genomic instability, or heritable mutations if unrepaired or repaired erroneously, leading to outcomes like chromosomal translocations, deletions, or insertions that underpin diseases including cancer.^[3]^[8] In mammalian cells, endogenous DSBs arise at rates of 10–50 per cell per day under normal conditions, reflecting routine physiological stresses despite cellular safeguards.^[9] To avert catastrophe, cells promptly activate repair mechanisms such as homologous recombination or non-homologous end joining.^[10]

Primary Causes

Double-strand breaks (DSBs) in DNA arise from a variety of endogenous and exogenous sources, each contributing to genomic instability if not properly managed. Endogenous causes primarily stem from normal cellular processes that inadvertently damage the DNA backbone. For instance, replication fork collapse occurs when replication machinery stalls at obstacles such as nucleotide shortages or unusual secondary structures, leading to DSB formation through the cleavage of stalled intermediates during S-phase progression.^[11] Transcription-associated damage results from conflicts between the transcription and replication machineries, where RNA polymerase complexes generate R-loops—RNA:DNA hybrids—that destabilize the DNA and induce breaks, particularly in regions with high transcriptional activity.^[11] In immune cells, programmed DSBs are deliberately introduced during V(D)J recombination by the RAG endonuclease complex to assemble variable regions of immunoglobulin and T-cell receptor genes, while class-switch recombination in B cells involves activation-induced cytidine deaminase (AID) generating DSBs to facilitate antibody isotype switching.^[11] Reactive oxygen species (ROS), produced as byproducts of mitochondrial respiration and other metabolic activities, also contribute to endogenous DSBs by oxidizing the DNA sugar-phosphate backbone, with estimates suggesting they account for a significant portion of spontaneous breaks under normal physiological conditions.^[12] Exogenous causes introduce DSBs through environmental or therapeutic exposures that directly assault DNA integrity. Ionizing radiation, such as X-rays and gamma rays, generates DSBs via indirect radiolysis of water molecules producing reactive radicals that abstract hydrogen atoms from the deoxyribose sugar, often resulting in clustered lesions—multiple damages within a few base pairs—that complicate repair.^[11] Chemotherapeutic agents like bleomycin cause DSBs by binding DNA and generating free radicals that cleave both strands, mimicking radiation effects in cancer treatment.^[11] Topoisomerase inhibitors, including etoposide and camptothecin, stabilize cleavage complexes during DNA unwinding, converting single-strand breaks into DSBs upon encounter with the replication fork, particularly exacerbating damage in proliferating cells.^[11] The frequency of DSBs is context-dependent, with endogenous sources yielding approximately 10–50 breaks per mammalian cell per day, rising significantly during S and G2 phases due to replication stress that amplifies fork collapse and transcription-replication collisions.^[11] Unrepaired DSBs from exogenous sources like radiation can trigger cell death pathways, underscoring their cytotoxic potential.^[13]

Major Repair Pathways

Homologous Recombination Pathways

Homologous recombination (HR) is a conservative, template-dependent mechanism for repairing double-strand breaks (DSBs) that utilizes a homologous DNA sequence, typically the sister chromatid, to accurately restore the original genetic information with minimal errors. This pathway is predominantly active during the S and G2 phases of the cell cycle, when a suitable template is available, and it contrasts with error-prone alternatives by prioritizing fidelity over speed. HR proceeds through a series of coordinated steps initiated by DSB recognition and end processing, ensuring high-fidelity repair that preserves genome integrity. The process begins with end resection, where the MRN complex (consisting of MRE11, RAD50, and NBS1) together with CtIP initiates the 5'-3' degradation of DSB ends to generate long 3' single-stranded DNA (ssDNA) overhangs, exposing homologous sequences for pairing. These ssDNA tails are initially bound by replication protein A (RPA), which is subsequently displaced by the recombinase RAD51 to form a nucleoprotein filament capable of searching for and invading the homologous donor duplex. Assembly of the RAD51 filament is facilitated by mediator proteins including BRCA1, BRCA2, PALB2, and RAD51 paralogs (RAD51B, RAD51C, RAD51D, XRCC2, XRCC3), which stabilize the filament and promote strand exchange. This invasion forms a displacement loop (D-loop), initiating DNA synthesis to copy the template sequence.^[2]^[14] One major subpathway is the canonical double-strand break repair (DSBR) model, where both DSB ends engage the homologous template, leading to the formation of double Holliday junctions (dHJs). After initial strand invasion by one end and DNA synthesis, the second DSB end is captured, and branch migration extends the heteroduplex regions. The dHJs are then resolved either by dissolution via the BTR complex (BLM helicase, TOP3A topoisomerase, and RMI1/2) to yield non-crossover products or by endonucleolytic resolution using GEN1 or MUS81-EME1 to produce both crossover and non-crossover outcomes. This model, proposed by Szostak et al. in 1983,^[1] accounts for both gene conversion and potential chromosomal crossovers observed in meiotic and mitotic recombination. DSBR ensures conservative repair but can introduce genetic rearrangements if crossovers occur between non-sister chromatids. In contrast, synthesis-dependent strand annealing (SDSA) is a non-crossover subpathway that predominates in mitotic cells for gene conversion without exchange. Following D-loop formation and extensive DNA synthesis from the invading strand, the newly synthesized arm is displaced from the template and anneals directly to the homologous sequences on the other resected DSB end, followed by gap filling and ligation. This process avoids second-end capture and Holliday junction formation, minimizing crossover risks. Evidence for SDSA emerged from studies in Drosophila showing efficient copying of ectopic sequences without reciprocal exchange, as demonstrated by Nassif et al. in 1994. SDSA relies on the same initial resection and invasion machinery but is promoted by helicases like SRS2 in yeast that unwind extended D-loops to facilitate annealing. Break-induced replication (BIR) addresses one-ended DSBs, such as those arising from collapsed replication forks or eroded telomeres, where only one end can invade a homologous template. The invading 3' end primes semi-conservative DNA replication that proceeds unidirectionally over long distances, often hundreds of kilobases, using standard replication factors like POLδ and PCNA after an initial RAD51-dependent invasion phase. Unlike DSBR or SDSA, BIR results in conservative replication of the donor sequence without restoring the second end, leading to loss of heterozygosity distal to the break. This pathway is particularly vital in telomerase-deficient cells for telomere maintenance and is associated with higher mutagenesis due to error-prone polymerases involved in later stages. Seminal work as reviewed by Haber in 2001 highlighting its role in repairing terminal deletions. Key regulators include PIF1 helicase, which limits excessive BIR to prevent genomic instability.^[15] Single-strand annealing (SSA) is a homology-directed but mutagenic HR variant that operates when repeats flank the DSB, bypassing the need for an intact sister chromatid. Extensive resection by EXO1 or DNA2 exposes complementary sequences in direct repeats, which anneal via RAD52 mediation, followed by removal of non-annealed flaps by ERCC1-XPF and ligation. This results in deletion of the intervening sequence between repeats, introducing loss-of-heterozygosity and potential genomic rearrangements. SSA is RAD51-independent but suppressed in S/G2 to favor canonical HR, and it predominates in G1 or in HR-deficient contexts. The mechanism was first modeled by Lin et al. in 1984 using plasmid recombination in mammalian cells, establishing its role in end-to-end joining via homology. Overall, HR subpathways achieve near-zero error rates for short-tract repair in DSBR and SDSA, but BIR and SSA can promote instability through structural variations.^[14]

End-Joining Pathways

End-joining pathways repair double-strand breaks (DSBs) through homology-independent or microhomology-dependent mechanisms that rapidly ligate broken DNA ends without requiring an extensive homologous template, though both are inherently error-prone and can introduce insertions or deletions at repair junctions.^[16] These pathways include classical non-homologous end joining (NHEJ), which directly rejoins ends with minimal processing, and microhomology-mediated end joining (MMEJ, also known as alternative end joining or alt-EJ), which anneals short homologous sequences for alignment.^[13] Unlike homologous recombination, end-joining is faster but less accurate, often leading to genomic instability if over-relied upon.^[16] Non-homologous end joining (NHEJ) is the predominant DSB repair pathway in mammalian cells, active throughout the cell cycle but especially dominant in G0/G1 and early S phases.^[17] The process begins with the Ku70/Ku80 heterodimer (Ku) rapidly binding to free DNA ends, forming a ring around the break to protect against nuclease degradation and recruit other factors.^[16] Ku then tethers the ends in a synaptic complex and activates DNA-dependent protein kinase catalytic subunit (DNA-PKcs), which autophosphorylates to facilitate end processing.^[16] For incompatible ends, such as those with overhangs or hairpins, the Artemis nuclease—activated by the DNA-PKcs/Artemis complex—trims or opens structures to generate ligatable termini.^[16] Final ligation is performed by the XRCC4-DNA ligase IV (LIG4) complex, stabilized by XRCC4-like factor (XLF), which seals the nick and completes repair.^[16] This core machinery enables rapid synapsis and end-tethering, minimizing diffusion of breaks.^[16] NHEJ preserves the original sequence more faithfully than other end-joining routes when ends are compatible, with error-free repairs occurring in 35–75% of cases for blunt or cohesive ends; however, it introduces small insertions or deletions (indels) in the remaining 25–65%, particularly at complex or damaged termini.^[18] These alterations typically involve 1–4 nucleotide changes, arising from limited fill-in or exonuclease activity during processing.^[19] Microhomology-mediated end joining (MMEJ) serves as a backup mechanism, utilizing short stretches of 2–20 base pairs of microhomology flanking the DSB for end annealing, and is particularly active in cells deficient for homologous recombination, such as BRCA1/2 mutants.^[13]^[19] Initiation involves poly(ADP-ribose) polymerase 1 (PARP1) binding to DNA ends and promoting limited 5' resection by the MRN complex (MRE11-RAD50-NBS1) to expose microhomologies.^[13] DNA polymerase θ (Polθ) then anneals the microhomologous regions, fills in gaps via its polymerase activity, and flaps out non-homologous flaps via its helicase domain, generating larger deletions than NHEJ.^[13] Ligation is completed by DNA ligase III (LIG3) in complex with XRCC1, independent of the LIG4 pathway.^[13] MMEJ occurs throughout the cell cycle but is suppressed in normal conditions by NHEJ and homologous recombination factors.^[13] MMEJ is highly mutagenic, invariably producing deletions by excising the region between microhomologies plus one copy of the homology itself, often resulting in 10–100 base pair losses at junctions—far more extensive than NHEJ's small indels—and additional insertions from Polθ's error-prone synthesis.^[19] This pathway's reliance on microhomology distinguishes it from NHEJ's direct tethering, leading to greater sequence loss but enabling repair in contexts where clean ends are unavailable.^[13]

Regulation of Repair Pathways

DNA Damage Response Mechanisms

The DNA damage response (DDR) to double-strand breaks (DSBs) initiates a cascade of signaling events that detect the lesion, amplify the signal, and coordinate cellular decisions to halt proliferation until repair is achieved or, if irreparable, trigger cell death. This response is primarily orchestrated by the ataxia-telangiectasia mutated (ATM) kinase for direct DSBs and the ataxia-telangiectasia and Rad3-related (ATR) kinase for replication-associated damage, leading to the activation of checkpoints that arrest the cell cycle at key transitions. These mechanisms ensure genomic integrity by recruiting repair factors and preventing the propagation of mutations.^[20] ATM activation occurs rapidly upon DSB sensing by the MRE11-RAD50-NBS1 (MRN) complex, which recruits and autophosphorylates ATM at serine 1981, enabling its kinase activity. Activated ATM then phosphorylates histone H2AX at serine 139, forming γ-H2AX foci that serve as platforms for further signaling. These foci recruit mediator of DNA damage checkpoint protein 1 (MDC1), which binds directly to γ-H2AX via its BRCT domains, amplifying ATM signaling and facilitating the accumulation of downstream effectors such as 53BP1 and BRCA1 at the break site. 53BP1 promotes non-homologous end joining by shielding ends from resection, while BRCA1 supports homologous recombination through its ubiquitin ligase activity in complex with BARD1. This hierarchical recruitment establishes a chromatin-bound signaling hub essential for DSB coordination.^[21]^[22]^[23] In contrast, ATR activation is prominent in replication-associated DSBs, where stalled forks generate extensive single-stranded DNA (ssDNA) coated by replication protein A (RPA). RPA-ssDNA recruits the ATR-interacting protein (ATRIP), which docks the ATR-ATRIP complex to the site, while TOPBP1 or ETAA1 stimulates ATR kinase activity. This pathway intersects DSB repair by stabilizing forks and promoting resection to generate substrates for homologous recombination, particularly during S phase. ATR phosphorylates checkpoint kinase 1 (CHK1) at serine 345, amplifying the response.^[24]^[25]^[26] The DDR activates multiple checkpoint pathways to enforce cell cycle arrests, allowing time for repair. The G1/S checkpoint is mediated by ATM-CHK2-p53 signaling, where CHK2 phosphorylates p53 at serine 20, stabilizing it to transcriptionally induce p21 and inhibit cyclin-dependent kinase 2 (CDK2), preventing S-phase entry. Intra-S phase arrest occurs via ATR-CHK1, which phosphorylates CDC25A for its degradation, slowing replication fork progression. The G2/M checkpoint, activated by both ATM-CHK2 and ATR-CHK1, inhibits CDC25C to block CDK1 activation and mitotic entry. These arrests are p53-dependent in G1 but more reliant on CHK1/2 in S/G2, collectively pausing the cell cycle in response to DSBs.^[27]^[28]^[20] The Fanconi anemia (FA) pathway, though primarily dedicated to interstrand crosslink repair, intersects DSB responses through monoubiquitination of FANCD2-FANCI by the FA core complex upon DNA damage sensing. Ubiquitinated FANCD2 accumulates at stalled forks and DSBs, recruiting nucleases like FAN1 to promote end resection and homologous recombination, thereby linking ICL-induced DSBs to high-fidelity repair. This coordination enhances DSB repair efficiency in contexts of replication stress.^[29]^[30]^[31] Recent studies have uncovered additional layers of regulation involving RNA molecules, which actively influence DSB repair outcomes. Nascent transcripts and other RNAs can modulate end-joining pathways and homologous recombination by facilitating protein recruitment or altering chromatin structure at break sites, providing a sequence-specific regulatory mechanism that enhances repair fidelity.^[32] Repair foci emerge as dynamic nuclear structures at DSB sites, nucleated by γ-H2AX and MDC1 to concentrate repair factors such as 53BP1, BRCA1, and MRN into liquid-like condensates via phase separation. These foci facilitate efficient signaling and factor exchange, with proteins diffusing in and out to orchestrate repair without permanent sequestration. DSB-induced foci typically form within minutes and resolve upon repair completion, serving as visible markers of active DDR.^[33]^[34]^[35] If DSBs remain unrepaired, the DDR promotes apoptosis through p53 activation, where stabilized p53 transcriptionally upregulates pro-apoptotic effectors like BAX, leading to mitochondrial outer membrane permeabilization and caspase activation. This p53-BAX axis eliminates cells with persistent genomic instability, preventing tumorigenesis. The DDR thus influences pathway selection by modulating chromatin accessibility and factor availability at breaks.^[36]^[37]

Factors Influencing Pathway Selection

The choice of double-strand break (DSB) repair pathway is profoundly influenced by the physical characteristics of the DNA ends generated by the break. Clean, blunt, or minimally damaged ends are preferentially repaired by non-homologous end joining (NHEJ), as this pathway efficiently ligates compatible termini without extensive processing.^[38] In contrast, "dirty" ends featuring overhangs, chemical modifications, or secondary structures often require end processing, which can favor homologous recombination (HR) if resection occurs to generate single-stranded DNA tails compatible with strand invasion. Resected ends, in particular, commit the break to HR by preventing NHEJ factor binding and promoting the recruitment of resection nucleases like MRN and EXO1.^[39] Cell cycle phase serves as a primary determinant of pathway selection, ensuring error-free repair when possible. NHEJ predominates in G1 phase, where the absence of a sister chromatid template limits HR; here, 53BP1 accumulates at DSB sites to shield ends from resection, facilitating rapid NHEJ ligation.00656-9) In S and G2 phases, cyclin-dependent kinase 1 (CDK1) phosphorylates CtIP, activating end resection and thereby suppressing NHEJ while promoting HR using the newly replicated sister chromatid as a template.^[40] This temporal regulation minimizes mutagenesis, as HR fidelity is higher post-replication.^[41] Antagonistic interactions between key regulators further fine-tune pathway choice. The proteins 53BP1 and BRCA1 compete at DSB sites: 53BP1 promotes NHEJ by inhibiting resection and recruiting RIF1 to compact chromatin around breaks, whereas BRCA1 counteracts this by promoting resection through RAP80 displacement and CtIP activation, thereby favoring HR.^[42] Pharmacological interventions like PARP inhibitors exacerbate this balance; by trapping PARP1 on DNA and inducing replication fork collapse into DSBs, they shift repair toward microhomology-mediated end joining (MMEJ) in HR-deficient cells, where NHEJ and HR are compromised, leading to synthetic lethality.^[43] Organismal context also modulates pathway preferences, reflecting evolutionary adaptations to genomic stability needs. In yeast, HR is the dominant pathway for DSB repair due to efficient homologous template availability and minimal reliance on NHEJ, which is error-prone and less utilized.^[44] Mammalian cells, however, balance NHEJ and HR, with NHEJ handling ~80% of breaks for rapid repair, while higher eukaryotes in HR-deficient states increasingly invoke alternative end-joining (alt-EJ, including MMEJ) to compensate.^[45] During meiosis, SPO11-induced DSBs are exclusively repaired via HR to generate crossovers essential for chromosome segregation; factors like MLH1 ensure interference and proper resolution of double Holliday junctions into crossovers.^[46] The origin of the DSB dictates pathway utilization to suit biological context. Replication-associated DSBs, often arising from fork collapse, preferentially engage break-induced replication (BIR), a HR variant that uses long-tract synthesis from a single end to restart forks and prevent loss of genetic information.^[47] In contrast, programmed DSBs during V(D)J recombination in lymphocytes are strictly repaired by NHEJ to join variable (V), diversity (D), and joining (J) gene segments, enabling antigen receptor diversity while suppressing error-prone alternatives.^[48]

Consequences of Defective Repair

Implications for Aging

Deficiencies in double-strand break (DSB) repair contribute to the accumulation of unrepaired DSBs in aging cells, manifesting as persistent γ-H2AX foci that indicate ongoing DNA damage response activation.^[49] This persistence reflects a failure to resolve breaks efficiently, leading to chronic genomic instability. Additionally, reliance on alternative non-homologous end joining (alt-NHEJ) for telomere maintenance results in telomere shortening, exacerbating cellular senescence and organismal aging.^[50] The decline in non-homologous end joining (NHEJ) efficiency with age, partly due to reduced Ku80 protein levels, heightens genomic instability by impairing the repair of DSBs in non-dividing cells.^[51] Similarly, homologous recombination (HR) is compromised through downregulation of BRCA1 expression, which promotes error-prone repair and mutation accumulation as cells age.^[52] Progeroid syndromes provide compelling evidence for the link between DSB repair defects and accelerated aging; for instance, Werner syndrome arises from mutations in the WRN helicase, which promotes classical NHEJ and inhibits alt-NHEJ, and its deficiency leads to genomic instability, premature cellular senescence, and organismal decline.^[53]^[54] Oxidative stress, a hallmark of aging, generates excessive DSBs that overwhelm repair capacities, triggering senescence through upregulation of p16 and p21 pathways that enforce irreversible cell cycle arrest.^[55] In mouse models with DSB repair deficiencies, such as those lacking key NHEJ or HR components, phenotypes like frailty, reduced lifespan, and tissue dysfunction are accelerated, mirroring natural aging processes.^[56]

Role in Cancer Development

Defects in double-strand break (DSB) repair pathways significantly contribute to cancer development by promoting genomic instability, a hallmark that enables tumor initiation and progression. Mutations in key homologous recombination (HR) genes, such as BRCA1 and BRCA2, lead to HR deficiency (HRD), forcing cells to rely on error-prone alternatives like non-homologous end-joining (NHEJ) and microhomology-mediated end joining (MMEJ), which generate insertions/deletions (indels) and structural variants that drive tumorigenesis. For instance, BRCA1/2 loss is a frequent driver in various cancers, impairing accurate DSB repair and resulting in elevated mutation burdens. Similarly, mutations in NHEJ components, such as LIG4, disrupt precise end ligation, increasing chromosomal translocations observed in lymphomas and other hematologic malignancies. Unrepaired or misrepaired DSBs exacerbate genomic instability, facilitating rapid evolutionary changes in cancer cells, including chromothripsis—a catastrophic shattering and reassembly of chromosomes that generates complex rearrangements. This process is particularly prevalent in tumors with DSB repair deficiencies, where persistent breaks lead to oncogenic amplifications, deletions, and fusions that promote progression. Evidence from hereditary syndromes underscores this link: germline BRCA1/2 mutations confer high lifetime risks of breast (up to 72%) and ovarian (up to 44%) cancers due to inherited HRD. In sporadic cancers, co-mutations in TP53, which impairs DNA damage response (DDR) coordination, compound DSB repair defects, accelerating malignant transformation across tumor types. Therapeutically, these vulnerabilities enable targeted interventions, such as PARP inhibitors, which exploit synthetic lethality in HR-deficient cells by trapping PARP on DNA and causing replication fork collapse, selectively killing BRCA-mutant tumors while sparing normal cells. Recent post-2020 CRISPR screens have identified novel synthetic lethal interactions in DSB repair pathways, revealing tumor-specific dependencies like ATM or KEAP1 loss that sensitize cancers to DDR inhibitors beyond BRCA contexts, with comprehensive genetic catalogs as of 2025 further mapping key repair interactions.^[57]

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The decision to repair a DSB by NHEJ or HR is made primarily at the level of DSB end resection, which is inhibited by the Ku complex in G1 and promoted by the ...Missing: seminal | Show results with:seminal
[40]
How cells ensure correct repair of DNA double-strand breaks - PMC
Whereas HR allows faithful DSB repair and healthy cell growth, NHEJ has higher potential to contribute to mutations and malignancy. Many regulatory mechanisms ...
[41]
53BP1, BRCA1, and the Choice between Recombination and End ...
Abstract. When DNA double-strand breaks occur, the cell cycle stage has a major influence on the choice of the repair pathway employed.
[42]
Nonhomologous end joining drives poly(ADP-ribose) polymerase ...
PARP inhibition is thought to induce accumulation of SSBs, which are converted to DSBs by collisions with replication machinery. The inability of HR-deficient ...Nonhomologous End Joining... · Results · Parp Inhibition Induces...Missing: shift | Show results with:shift
[43]
Regulation of DNA double-strand break repair pathway choice
Dec 24, 2007 · In yeast and mammalian cells, 25-50% of nuclease DSBs are repaired by precise NHEJ; note that these are minimum estimates because these ...
[44]
Repair of DNA Double-Strand Breaks by the Non-homologous End ...
NHEJ is the predominant pathway in human cells and repairs up to ~80% of all DSBs (3). During NHEJ, DNA ends are brought together by a multi-protein synaptic ...
[45]
Mlh1-Mlh3, a Meiotic Crossover and DNA Mismatch Repair Factor ...
Background: Meiotic crossing over requires resolution of Holliday junctions through actions of the DNA mismatch repair factor Mlh1-Mlh3.
[46]
Repair of DNA breaks by break-induced replication (BIR) - PMC - NIH
Nov 2, 2022 · Break-induced replication (BIR) repairs one-ended DNA breaks by invading a broken end into a template, synthesizing new DNA, and is associated ...1.1. Dna Damage Leading To... · Figure 1. Dsb Repair... · 4.0. Microhomology Mediated...<|separator|>
[47]
The (Lack of) DNA Double-Strand Break Repair Pathway Choice ...
In this review, we present V(D)J recombination as a relevant biological setting to investigate factors influencing DSB repair pathway choice, specifically those ...
[48]
Accumulation of DNA Damage in Hematopoietic Stem and ...
... γH2AX-foci per cell and donor age (Fig. 2, upper panels) or telomere ... persisting γH2AX-foci may indicate the presence of unrepaired or misrepaired DSBs.
[49]
Mechanisms of telomere loss and their consequences for ...
Consistent with a predominant role for A-NHEJ in repair of telomeric DSBs ... Similarly, aging normal tissues also accumulate DSB repair foci near telomeres.
[50]
Changes in DNA repair during aging - Oxford Academic
Defects in DNA maintenance may lead to accelerated aging. Notable examples are mice deficient in NHEJ or mice deficient in TCR ( 107 , 108 ). It has to be ...
[51]
(PDF) Impairment of BRCA1-related DNA Double Strand Break ...
Aug 9, 2025 · We show that DSBs accumulate in primordial follicles with age. In parallel, expression of key DNA DSB repair genes BRCA1, MRE11, Rad51, and ATM, ...
[52]
WRN regulates pathway choice between classical and alternative ...
Dec 6, 2016 · Werner Syndrome (WS) is an autosomal-recessive genetic disorder characterized by premature ageing and DNA repair defects because of mutations in ...
[53]
The accelerated aging phenotype in Sod1−/− mice is correlated to ...
Sod1−/− mice have high levels of oxidative damage and DNA double strand breaks. · Sod1−/− mice show increased cellular senescence, e.g., p16, p21 and β-gal+ ...
[54]
DNA repair‐deficient premature aging models display accelerated ...
These findings highlight that mouse models with deficiencies in DNA repair, unlike other premature aging models, display accelerated epigenetic age.