scholarly journals Analysis of NHEJ-Based DNA Repair after CRISPR-Mediated DNA Cleavage

2021 ◽  
Vol 22 (12) ◽  
pp. 6397
Author(s):  
Beomjong Song ◽  
Soyeon Yang ◽  
Gue-Ho Hwang ◽  
Jihyeon Yu ◽  
Sangsu Bae
Keyword(s):  
Genome Editing ◽  
Dna Cleavage ◽  
Strand Break ◽  
Insertion Mutation ◽  
End Joining ◽  
Dsb Repair ◽  
Exogenous Dna ◽  
Average Value ◽  
Dna Oligonucleotides ◽  
Mutation Ratio

Genome editing using CRISPR-Cas9 nucleases is based on the repair of the DNA double-strand break (DSB). In eukaryotic cells, DSBs are rejoined through homology-directed repair (HDR), non-homologous end joining (NHEJ) or microhomology-mediated end joining (MMEJ) pathways. Among these, it is thought that the NHEJ pathway is dominant and occurs throughout a cell cycle. NHEJ-based DSB repair is known to be error-prone; however, there are few studies that delve into it deeply in endogenous genes. Here, we quantify the degree of NHEJ-based DSB repair accuracy (termed NHEJ accuracy) in human-originated cells by incorporating exogenous DNA oligonucleotides. Through an analysis of joined sequences between the exogenous DNA and the endogenous target after DSBs occur, we determined that the average value of NHEJ accuracy is approximately 75% in maximum in HEK 293T cells. In a deep analysis, we found that NHEJ accuracy is sequence-dependent and the value at the DSB end proximal to a protospacer adjacent motif (PAM) is relatively lower than that at the DSB end distal to the PAM. In addition, we observed a negative correlation between the insertion mutation ratio and the degree of NHEJ accuracy. Our findings would broaden the understanding of Cas9-mediated genome editing.

Impact of chromatin context on Cas9-induced DNA double-strand break repair pathway balance

2020 ◽  
Author(s):  
Ruben Schep ◽  
Eva K. Brinkman ◽  
Christ Leemans ◽  
Xabier Vergara ◽  
Ben Morris ◽  
...  
Keyword(s):  
Genome Editing ◽  
Strand Break ◽  
Double Strand Break ◽  
Repair Pathway ◽  
End Joining ◽  
Dsb Repair ◽  
Dna Double Strand Break ◽  
Repair Pathways ◽  
Non Homologous End Joining ◽  
The Impact

AbstractDNA double-strand break (DSB) repair is mediated by multiple pathways, including classical non-homologous end-joining pathway (NHEJ) and several homology-driven repair pathways. This is particularly important for Cas9-mediated genome editing, where the outcome critically depends on the pathway that repairs the break. It is thought that the local chromatin context affects the pathway choice, but the underlying principles are poorly understood. Using a newly developed multiplexed reporter assay in combination with Cas9 cutting, we systematically measured the relative activities of three DSB repair pathways as function of chromatin context in >1,000 genomic locations. This revealed that NHEJ is broadly biased towards euchromatin, while microhomology-mediated end-joining (MMEJ) is more efficient in specific heterochromatin contexts. In H3K27me3-marked heterochromatin, inhibition of the H3K27 methyltransferase EZH2 shifts the balance towards NHEJ. Single-strand templated repair (SSTR), often used for precise CRISPR editing, competes with MMEJ, and this competition is weakly associated with chromatin context. These results provide insight into the impact of chromatin on DSB repair pathway balance, and guidance for the design of Cas9-mediated genome editing experiments.

scholarly journals A genetically encoded inhibitor of 53BP1 to stimulate homology-based gene editing

2016 ◽  
Author(s):  
Marella D. Canny ◽  
Leo C.K. Wan ◽  
Amélie Fradet-Turcotte ◽  
Alexandre Orthwein ◽  
Nathalie Moatti ◽  
...  
Keyword(s):  
Genome Editing ◽  
Genome Engineering ◽  
Cell Types ◽  
Strand Break ◽  
End Joining ◽  
Dsb Repair ◽  
Non Homologous End Joining ◽  
G1 Cells ◽  
Programmable Nucleases ◽  
End Resection

AbstractThe expanding repertoire of programmable nucleases such as Cas9 brings new opportunities in genetic medicine1–3. In many cases, these nucleases are engineered to induce a DNA double-strand break (DSB) to stimulate precise genome editing by homologous recombination (HR). However, HR efficiency is nearly always hindered by competing DSB repair pathways such as non-homologous end-joining (NHEJ). HR is also profoundly suppressed in non-replicating cells, thus precluding the use of homology-based genome engineering in a wide variety4 of cell types. Here, we report the development of a genetically encoded inhibitor of 53BP1 (known as TP53BP1), a regulator of DSB repair pathway choice5. 53BP1 promotes NHEJ over HR by suppressing end resection, the formation of 3-prime single-stranded DNA tails, which is the rate-limiting step in HR initiation. 53BP1 also blocks the recruitment of the HR factor BRCA1 to DSB sites in G1 cells4,6. The inhibitor of 53BP1 (or i53) was identified through the screening of a massive combinatorial library of engineered ubiquitin variants by phage display7. i53 binds and occludes the ligand binding site of the 53BP1 Tudor domain with high affinity and selectivity, blocking its ability to accumulate at sites of DNA damage. i53 is a potent selective inhibitor of 53BP1 and enhances gene targeting and chromosomal gene conversion, two HR-dependent reactions. Finally, i53 can also activate HR in G1 cells when combined with the activation of end-resection and KEAP1 inhibition. We conclude that 53BP1 inhibition is a robust tool to enhance precise genome editing by canonical HR pathways.

scholarly journals Concurrent genome and epigenome editing by CRISPR-mediated sequence replacement

BMC Biology ◽  
2019 ◽  
Vol 17 (1) ◽  
Author(s):  
Jes Alexander ◽  
Gregory M. Findlay ◽  
Martin Kircher ◽  
Jay Shendure
Keyword(s):  
Genome Editing ◽  
Cpg Island ◽  
Strand Break ◽  
End Joining ◽  
Exogenous Dna ◽  
Cpg Dinucleotides ◽  
Epigenome Editing ◽  
Homology Directed Repair ◽  
Non Homologous End Joining

Abstract Background Recent advances in genome editing have facilitated the direct manipulation of not only the genome, but also the epigenome. Genome editing is typically performed by introducing a single CRISPR/Cas9-mediated double-strand break (DSB), followed by non-homologous end joining (NHEJ)- or homology-directed repair-mediated repair. Epigenome editing, and in particular methylation of CpG dinucleotides, can be performed using catalytically inactive Cas9 (dCas9) fused to a methyltransferase domain. However, for investigations of the role of methylation in gene silencing, studies based on dCas9-methyltransferase have limited resolution and are potentially confounded by the effects of binding of the fusion protein. As an alternative strategy for epigenome editing, we tested CRISPR/Cas9 dual cutting of the genome in the presence of in vitro methylated exogenous DNA, with the aim of driving replacement of the DNA sequence intervening the dual cuts via NHEJ. Results In a proof of concept at the HPRT1 promoter, successful replacement events with heavily methylated alleles of a CpG island resulted in functional silencing of the HPRT1 gene. Although still limited in efficiency, our study demonstrates concurrent epigenome and genome editing in a single event. Conclusions This study opens the door to investigations of the functional consequences of methylation patterns at single CpG dinucleotide resolution. Our results furthermore support the conclusion that promoter methylation is sufficient to functionally silence gene expression.

scholarly journals Regulatory and Functional Involvement of Long Non-Coding RNAs in DNA Double-Strand Break Repair Mechanisms

Cells ◽  
2021 ◽  
Vol 10 (6) ◽  
pp. 1506
Author(s):  
Angelos Papaspyropoulos ◽  
Nefeli Lagopati ◽  
Ioanna Mourkioti ◽  
Andriani Angelopoulou ◽  
Spyridon Kyriazis ◽  
...  
Keyword(s):  
Therapeutic Potential ◽  
Strand Break ◽  
Dna Double Strand Breaks ◽  
End Joining ◽  
Dsb Repair ◽  
Repair Mechanisms ◽  
Non Coding Rnas ◽  
Repair Pathways ◽  
Non Homologous End Joining ◽  
Living Organisms

Protection of genome integrity is vital for all living organisms, particularly when DNA double-strand breaks (DSBs) occur. Eukaryotes have developed two main pathways, namely Non-Homologous End Joining (NHEJ) and Homologous Recombination (HR), to repair DSBs. While most of the current research is focused on the role of key protein players in the functional regulation of DSB repair pathways, accumulating evidence has uncovered a novel class of regulating factors termed non-coding RNAs. Non-coding RNAs have been found to hold a pivotal role in the activation of DSB repair mechanisms, thereby safeguarding genomic stability. In particular, long non-coding RNAs (lncRNAs) have begun to emerge as new players with vast therapeutic potential. This review summarizes important advances in the field of lncRNAs, including characterization of recently identified lncRNAs, and their implication in DSB repair pathways in the context of tumorigenesis.

scholarly journals Double-strand DNA breaks recruit the centromeric histone CENP-A

2009 ◽  
Vol 106 (37) ◽  
pp. 15762-15767 ◽  
Author(s):  
Samantha G. Zeitlin ◽  
Norman M. Baker ◽  
Brian R. Chapados ◽  
Evi Soutoglou ◽  
Jean Y. J. Wang ◽  
...  
Keyword(s):  
Dna Cleavage ◽  
Strand Break ◽  
Double Strand Breaks ◽  
Dna Breaks ◽  
End Joining ◽  
Strand Breaks ◽  
Double Strand Dna Breaks ◽  
Histone H3 Variant ◽  
Radiation Induced ◽  
Non Homologous End Joining

The histone H3 variant CENP-A is required for epigenetic specification of centromere identity through a loading mechanism independent of DNA sequence. Using multiphoton absorption and DNA cleavage at unique sites by I-SceI endonuclease, we demonstrate that CENP-A is rapidly recruited to double-strand breaks in DNA, along with three components (CENP-N, CENP-T, and CENP-U) associated with CENP-A at centromeres. The centromere-targeting domain of CENP-A is both necessary and sufficient for recruitment to double-strand breaks. CENP-A accumulation at DNA breaks is enhanced by active non-homologous end-joining but does not require DNA-PKcs or Ligase IV, and is independent of H2AX. Thus, induction of a double-strand break is sufficient to recruit CENP-A in human and mouse cells. Finally, since cell survival after radiation-induced DNA damage correlates with CENP-A expression level, we propose that CENP-A may have a function in DNA repair.

scholarly journals RAP80 suppresses the vulnerability of R-loops during DNA double-strand break repair

2021 ◽  
Author(s):  
Takaaki Yasuhara ◽  
Reona Kato ◽  
Motohiro Yamauchi ◽  
Yuki Uchihara ◽  
Lee Zou ◽  
...  
Keyword(s):  
Active Regions ◽  
Strand Break ◽  
Double Strand Breaks ◽  
Critical Component ◽  
Dna Double Strand Breaks ◽  
End Joining ◽  
Dsb Repair ◽  
Strand Breaks ◽  
Chromosome Translocations ◽  
Dna Double Strand Break

AbstractR-loops, consisting of ssDNA and DNA-RNA hybrids, are potentially vulnerable unless they are appropriately processed. Recent evidence suggests that R-loops can form in the proximity of DNA double-strand breaks (DSBs) within transcriptionally active regions. Yet, how the vulnerability of R-loops is overcome during DSB repair remains unclear. Here, we identify RAP80 as a factor suppressing the vulnerability of ssDNA in R-loops and chromosome translocations and deletions during DSB repair. Mechanistically, RAP80 prevents unscheduled nucleolytic processing of ssDNA in R-loops by CtIP. This mechanism promotes efficient DSB repair via transcription-associated end-joining dependent on BRCA1, Polθ, and LIG1/3. Thus, RAP80 suppresses the vulnerability of R-loops during DSB repair, thereby precluding genomic abnormalities in a critical component of the genome caused by deleterious R-loop processing.

scholarly journals cGAS guards against chromosome end-to-end fusions during mitosis and facilitates replicative senescence

2021 ◽  
Author(s):  
Xiaocui Li ◽  
Xiaojuan Li ◽  
Chen Xie ◽  
Sihui Cai ◽  
Mengqiu Li ◽  
...  
Keyword(s):  
Genome Stability ◽  
Mitotic Chromosome ◽  
Replicative Senescence ◽  
Genome Instability ◽  
Strand Break ◽  
End Joining ◽  
Dsb Repair ◽  
End To End ◽  
Non Homologous End Joining ◽  
Sting Pathway

AbstractAs a sensor of cytosolic DNA, the role of cyclic GMP-AMP synthase (cGAS) in innate immune response is well established, yet how its functions in different biological conditions remain to be elucidated. Here, we identify cGAS as an essential regulator in inhibiting mitotic DNA double-strand break (DSB) repair and protecting short telomeres from end-to-end fusion independent of the canonical cGAS-STING pathway. cGAS associates with telomeric/subtelomeric DNA during mitosis when TRF1/TRF2/POT1 are deficient on telomeres. Depletion of cGAS leads to mitotic chromosome end-to-end fusions predominantly occurring between short telomeres. Mechanistically, cGAS interacts with CDK1 and positions them to chromosome ends. Thus, CDK1 inhibits mitotic non-homologous end joining (NHEJ) by blocking the recruitment of RNF8. cGAS-deficient human primary cells are defective in entering replicative senescence and display chromosome end-to-end fusions, genome instability and prolonged growth arrest. Altogether, cGAS safeguards genome stability by controlling mitotic DSB repair to inhibit mitotic chromosome end-to-end fusions, thus facilitating replicative senescence.

Double strand break (DSB) repair pathways in plants and their application in genome engineering

2021 ◽  
pp. 27-62
Author(s):  
Natalja Beying ◽  
◽  
Carla Schmidt ◽  
Holger Puchta ◽  
◽  
...  
Keyword(s):  
Genome Engineering ◽  
Plant Cells ◽  
Strand Break ◽  
End Joining ◽  
Dsb Repair ◽  
Strand Breaks ◽  
Repair Mechanisms ◽  
Repair Pathways ◽  
Non Homologous End Joining ◽  
Underlying Mechanisms

In genome engineering, after targeted induction of double strand breaks (DSBs) researchers take advantage of the organisms’ own repair mechanisms to induce different kinds of sequence changes into the genome. Therefore, understanding of the underlying mechanisms is essential. This chapter will review in detail the two main pathways of DSB repair in plant cells, non-homologous end joining (NHEJ) and homologous recombination (HR) and sum up what we have learned over the last decades about them. We summarize the different models that have been proposed and set these into relation with the molecular outcomes of different classes of DSB repair. Moreover, we describe the factors that have been identified to be involved in these pathways. Applying this knowledge of DSB repair should help us to improve the efficiency of different types of genome engineering in plants.

scholarly journals Defining the mutation signatures of DNA polymerase θ in cancer genomes

NAR Cancer ◽  
2020 ◽  
Vol 2 (3) ◽  
Author(s):  
Taejoo Hwang ◽  
Shelley Reh ◽  
Yerkin Dunbayev ◽  
Yi Zhong ◽  
Yoko Takata ◽  
...  
Keyword(s):  
Cancer Cells ◽  
Dna Polymerase ◽  
Human Cancer ◽  
Strand Break ◽  
Base Substitution ◽  
Cancer Therapies ◽  
End Joining ◽  
Dsb Repair ◽  
Human Cancer Cells ◽  
Insertion And Deletion

Abstract DNA polymerase theta (POLQ)-mediated end joining (TMEJ) is a distinct pathway for mediating DNA double-strand break (DSB) repair. TMEJ is required for the viability of BRCA-mutated cancer cells. It is crucial to identify tumors that rely on POLQ activity for DSB repair, because such tumors are defective in other DSB repair pathways and have predicted sensitivity to POLQ inhibition and to cancer therapies that produce DSBs. We define here the POLQ-associated mutation signatures in human cancers, characterized by short insertions and deletions in a specific range of microhomologies. By analyzing 82 COSMIC (Catalogue of Somatic Mutations in Cancer) signatures, we found that BRCA-mutated cancers with a higher level of POLQ expression have a greatly enhanced representation of the small insertion and deletion signature 6, as well as single base substitution signature 3. Using human cancer cells with disruptions of POLQ, we further show that TMEJ dominates end joining of two separated DSBs (distal EJ). Templated insertions with microhomology are enriched in POLQ-dependent distal EJ. The use of this signature analysis will aid in identifying tumors relying on POLQ activity.

scholarly journals Using Transcriptomic Analysis to Assess Double-Strand Break Repair Activity: Towards Precise in Vivo Genome Editing

2020 ◽  
Vol 21 (4) ◽  
pp. 1380 ◽  
Author(s):  
Giovanni Pasquini ◽  
Virginia Cora ◽  
Anka Swiersy ◽  
Kevin Achberger ◽  
Lena Antkowiak ◽  
...  
Keyword(s):  
Genome Editing ◽  
Mammalian Cells ◽  
Time Course ◽  
Sequencing Analysis ◽  
End Joining ◽  
Dsb Repair ◽  
Repair Gene ◽  
Repair Pathways

Mutations in more than 200 retina-specific genes have been associated with inherited retinal diseases. Genome editing represents a promising emerging field in the treatment of monogenic disorders, as it aims to correct disease-causing mutations within the genome. Genome editing relies on highly specific endonucleases and the capacity of the cells to repair double-strand breaks (DSBs). As DSB pathways are cell-cycle dependent, their activity in postmitotic retinal neurons, with a focus on photoreceptors, needs to be assessed in order to develop therapeutic in vivo genome editing. Three DSB-repair pathways are found in mammalian cells: Non-homologous end joining (NHEJ); microhomology-mediated end joining (MMEJ); and homology-directed repair (HDR). While NHEJ can be used to knock out mutant alleles in dominant disorders, HDR and MMEJ are better suited for precise genome editing, or for replacing entire mutation hotspots in genomic regions. Here, we analyzed transcriptomic in vivo and in vitro data and revealed that HDR is indeed downregulated in postmitotic neurons, whereas MMEJ and NHEJ are active. Using single-cell RNA sequencing analysis, we characterized the dynamics of DSB repair pathways in the transition from dividing cells to postmitotic retinal cells. Time-course bulk RNA-seq data confirmed DSB repair gene expression in both in vivo and in vitro samples. Transcriptomic DSB repair pathway profiles are very similar in adult human, macaque, and mouse retinas, but not in ground squirrel retinas. Moreover, human-induced pluripotent stem-cell-derived neurons and retinal organoids can serve as well suited in vitro testbeds for developing genomic engineering approaches in photoreceptors. Our study provides additional support for designing precise in vivo genome-editing approaches via MMEJ, which is active in mature photoreceptors.

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