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Hairpin Capture of DNA End Structures reveals chromosomal DNA end structure with single nucleotide resolution

ABSTRACT: The structure of broken DNA ends is a critical determinant of the pathway used for DNA double strand break (DSB) repair. Here, we develop an approach, hairpin capture of DNA end structures (HCoDES), which elucidates chromosomal DNA end structures at single nucleotide resolution. HCoDES defines structures of physiologic DSBs generated by the RAG endonuclease, as well as those generated by nucleases widely used for genome editing. Analysis of G1-phase cells deficient in H2AX or 53BP1 reveals DNA ends that are frequently resected to form long single-stranded overhangs that can be repaired by mutagenic pathways. In addition to 3’ overhangs, many of these DNA ends unexpectedly form long 5’ single-stranded overhangs. The divergence in DNA end structures resolved by HCoDES suggests that H2AX and 53BP1 may have distinct activities in end protection. Thus, the high-resolution end structures obtained by HCoDES identify new features of DNA end processing during DSB repair. Single stranded DNA ligation of genomic DNA isolated from G1 arrested LigaseIV-/-, LigaseIV-/- 53BP1-/- and LigaseIV-/- H2AX-/- Abelson pre-B cells harboring site specific DSBs generated by the RAG recombinase, Cas9 endonuclease or Zinc Finger Endonuclease.

ORGANISM(S): Mus musculus

SUBMITTER: Jacqueline Payton

PROVIDER: E-GEOD-62534 | biostudies-arrayexpress |

REPOSITORIES: biostudies-arrayexpress

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Hairpin Capture of DNA End Structures reveals chromosomal DNA end structure with single nucleotide resolution

Project description:The structure of broken DNA ends is a critical determinant of the pathway used for DNA double strand break (DSB) repair. Here, we develop an approach, hairpin capture of DNA end structures (HCoDES), which elucidates chromosomal DNA end structures at single nucleotide resolution. HCoDES defines structures of physiologic DSBs generated by the RAG endonuclease, as well as those generated by nucleases widely used for genome editing. Analysis of G1-phase cells deficient in H2AX or 53BP1 reveals DNA ends that are frequently resected to form long single-stranded overhangs that can be repaired by mutagenic pathways. In addition to 3’ overhangs, many of these DNA ends unexpectedly form long 5’ single-stranded overhangs. The divergence in DNA end structures resolved by HCoDES suggests that H2AX and 53BP1 may have distinct activities in end protection. Thus, the high-resolution end structures obtained by HCoDES identify new features of DNA end processing during DSB repair.

2014-12-03 | GSE62534 | GEO

53BP1 cooperation with the REV7–shieldin complex underpins DNA structure-specific NHEJ

Project description:53BP1 governs a specialized, context-specific branch of the classical non-homologous end joining DNA double-strand break repair pathway. Mice lacking 53bp1 (also known as Trp53bp1) are immunodeficient owing to a complete loss of immunoglobulin class-switch recombination, and reduced fidelity of long-range V(D)J recombination. The 53BP1-dependent pathway is also responsible for pathological joining events at dysfunctional telomeres, and its unrestricted activity in Brca1-deficient cellular and tumour models causes genomic instability and oncogenesis. Cells that lack core non-homologous end joining proteins are profoundly radiosensitive, unlike 53BP1-deficient cells, which suggests that 53BP1 and its co-factors act on specific DNA substrates. Here we show that 53BP1 cooperates with its downstream effector protein REV7 to promote non-homologous end joining during class-switch recombination, but REV7 is not required for 53BP1-dependent V(D)J recombination. We identify shieldin—a four-subunit putative single-stranded DNA-binding complex comprising REV7, c20orf196 (SHLD1), FAM35A (SHLD2) and FLJ26957 (SHLD3)— as the factor that explains this specificity. Shieldin is essential for REV7-dependent DNA end-protection and non-homologous end joining during class-switch recombination, and supports toxic non-homologous end joining in Brca1-deficient cells, yet is dispensable for REV7-dependent interstrand cross-link repair. The 53BP1 pathway therefore comprises distinct double-strand break repair activities within chromatin and single-stranded DNA compartments, which explains both the immunological differences between 53bp1- and Rev7- deficient mice and the context specificity of the pathway.

2018-07-26 | PXD009650 | Pride

Shieldin/CST-dependent and independent functions of 53BP1 control DNA end-joining and repair pathway choice

Project description:53BP1 regulates DNA end-joining in lymphocytes, diversifying immune antigen receptors. This involves nucleosome-bound 53BP1 at DNA double-stranded breaks (DSBs) recruiting RIF1 and shieldin, a poorly understood DNA-binding complex. The 53BP1-RIF1-shieldin axis is pathological in BRCA1-mutated cancers, blocking homologous recombination (HR) and driving illegitimate non-homologous end-joining (NHEJ). However, how this axis regulates DNA end-joining and HR suppression remains unresolved. We investigated shieldin and its interplay with CST, a complex recently implicated in 53BP1-dependent activities. Immunophenotypically, mice lacking shieldin or CST are equivalent, with class-switch recombination co-reliant on both complexes. DNA damage-responsive signalling promotes shieldin-CST interaction, demonstrating shieldin as a DSB-specific CST adaptor. Furthermore, DNA polymerase ζ functions downstream of shieldin, establishing DNA fill-in synthesis as the physiological function of shieldin-CST. Lastly, 53BP1 suppresses HR and promotes NHEJ in BRCA1-deficient cells independently of shieldin. These findings showcase the resilience of the 53BP1 pathway, achieved through the collaboration of chromatin-bound 53BP1 complexes and DNA end-processing effector proteins.

2024-08-27 | PXD045534 | Pride

RIF1-ASF1-mediated high-order chromatin structure safeguards genome integrity

Project description:The 53BP1-RIF1 pathway antagonizes resection of DNA broken ends and confers PARP inhibitor sensitivity on BRCA1-mutated tumors. However, it is unclear how this pathway suppresses initiation of resection. Here, we identify ASF1 as a partner of RIF1 via an interacting manner similar to its interactions with histone chaperones CAF-1 and HIRA. ASF1 is recruited to distal chromatin flanking DNA breaks by 53BP1-RIF1 and promotes non-homologous end joining (NHEJ) using its histone chaperone activity. Epistasis analysis shows that ASF1 acts in the same NHEJ pathway as RIF1, but via a parallel pathway with the shieldin complex, which suppresses resection after initiation. Moreover, defects in end resection and homologous recombination (HR) in BRCA1-deficient cells are largely suppressed by ASF1 deficiency. Mechanistically, ASF1 compacts adjacent chromatin by heterochromatinization to protect broken DNA ends from BRCA1-mediated resection. Taken together, our findings identified a RIF1-ASF1 histone chaperone complex that promotes changes in high-order chromatin structure to stimulate the NHEJ pathway for DSB repair.

2022-02-04 | PXD031311 | Pride

Effect of Oral Administration of Methylene Blue MMX Tablets on Double Stranded DNA

Project description:Single Centre, open label assignment phase II clinical study. To evaluate the effect of oral 200mg Methylene Blue tablets (administered 8x25mg) prior to endoscopy on double stranded DNA breaks in colonic biopsy samples assessed by histone gamma H2AX analysis, compared to control biopsies.

| 2178654 | ecrin-mdr-crc

SHLD1 is dispensable for 53BP1-dependent V(D)J recombination but critical for productive class switch recombination

Project description:The shieldin (SHLD) complex, composed of SHLD1, SHLD2, SHLD3 and MAD2L2/REV7, acts downstream of 53BP1 to counteract DNA double-strand break (DSB) end-resection and promote non-homologous end-joining (NHEJ). While 53BP1 is essential for immunoglobulin heavy chain class switch recombination (CSR), long-range V(D)J recombination and for repair of RAG-induced DSBs in XLF-deficient cells, the role of SHLD in these activities remains elusive. Here, we report that contrary to 53BP1, SHLD1 is dispensable for lymphocyte development and V(D)J recombination, even in the sensitized XLF-deficient background or for the joining of distant V(D)J segments. By contrast, SHLD1 restricts resection at AID-induced DSB ends in both NHEJ-proficient and NHEJ-deficient B cells, providing an end-protection mechanism that permits productive CSR. Finally, we show that this end-protection function is required for orientation-specific joining of AID-initiated DSBs. We propose that 53BP1 promotes V(D)J recombination and CSR through two distinct mechanisms; the synapsis of V(D)J segments and switch regions within chromatin independently of SHLD and the protection of AID-DSB ends against resection mediated by SHLD.

2022-05-11 | GSE202567 | GEO

Role of 53BP1 in End Protection and DNA synthesis at DNA breaks [END-seq]

Project description:Double-strand break (DSB) repair choice is greatly influenced by the initial processing of DNA ends. 53BP1 limits the formation of recombinogenic single strand DNA (ssDNA) in BRCA1-deficient cells leading to defects in homologous recombination (HR). However, the exact mechanisms by which 53BP1 inhibits DSB resection remain unclear. Previous studies have identified two potential pathways: protection against exonucleases presumably through the Shieldin (SHLD) complex binding to ssDNA, and localized DNA synthesis through the (CTC1-STN1-TEN1) CST and DNA polymerase alpha (Polα) to counteract resection. We present evidence here that 53BP1-mediated exonuclease protection plays a more significant role than CST/Polα synthesis in countering hyper-resection at DSBs in G1 phase. Using a combinatorial approach of END-seq, SAR-seq, and RPA ChIP-seq, we directly assessed the extent of resection, DNA synthesis, and ssDNA, respectively, at AsiSI-induced DSBs. We show that in the presence of 53BP1, Polα-dependent DNA synthesis reduces the fraction of resected DSBs and the resection lengths. However, in the absence of 53BP1, Polα activity is sustained on ssDNA yet does not substantially counter resection. In contrast, Exo1 nuclease activity is essential for hyperresection in the absence of 53BP1. Thus, 53BP1 inhibits resection mainly through end-protection rather than by promoting fill-in.

2021-09-10 | GSE181669 | GEO

Role of 53BP1 in End Protection and DNA synthesis at DNA breaks [ChIP-seq]

2021-09-10 | GSE181668 | GEO

Role of 53BP1 in End Protection and DNA synthesis at DNA breaks [SAR-seq]

2021-09-10 | GSE181667 | GEO

A cell cycle switch in TRF2 controls t-loop dynamics and DNA secondary structure resolution across the genome

Project description:Telomere end-protection by the shelterin complex prevents DNA damage signalling and promiscuous repair at chromosome ends. Evidence suggests that the 3’ single-stranded telomere end can assemble into a lasso-like t-loop configuration, which has been proposed to safeguard chromosome ends from being recognized as DNA double strand breaks. Mechanisms must also exist to transiently disassemble t-loops to allow faithful telomere replication and to permit telomerase access to the 3’-end to solve the end replication problem. However, the regulation and physiological importance of t-loops in end-protection remains uncertain. Here, we identify a CDK phosphorylation site in the shelterin subunit, TRF2 (Ser365), whose dephosphorylation in S-phase by the PP6C/R3 phosphatase provides a narrow window during which the helicase RTEL1 is able to transiently access and unwind t-loops to facilitate telomere replication. Re-phosphorylation of TRF2 on Ser365 outside of S-phase is required to release RTEL1 from telomeres, which not only protects t-loops from promiscuous unwinding and inappropriate ATM activation, but also counteracts replication conflicts at DNA secondary structures arising within telomeres and across the genome. Hence, a phospho-switch in TRF2 coordinates assembly and disassembly of t-loops during the cell cycle, which protects telomeres from replication stress and an unscheduled DNA damage response.

2019-11-25 | PXD014843 | Pride

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