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Dual Processing of R-Loops and Topoisomerase I Induces Transcription-Dependent DNA Double-Strand Breaks
Agnese Cristini1, Giulia Ricci2, Sébastien Britton3
1Cancer Research Center of Toulouse, INSERM, Université de Toulouse, Université Toulouse III Paul Sabatier, CNRS, 31037 Toulouse, France; Sir William Dunn School of Pathology, University of Oxford, South Parks Road, Oxford OX1 3RE, UK.
Abstract:
Although accumulation of DNA damage and genomic instability in resting cells can cause neurodegenerative disorders, our understanding of how transcription produces DNA double-strand breaks (DSBs) is limited. Transcription-blocking topoisomerase I cleavage complexes (TOP1ccs) are frequent events that prime DSB production in non-replicating cells. Here, we report a mechanism of their formation by showing that they arise from two nearby single-strand breaks (SSBs) on opposing DNA strands: one SSB from the removal of transcription-blocking TOP1ccs by the TDP1 pathway and the other from the cleavage of R-loops by endonucleases, including XPF, XPG, and FEN1. Genetic defects in TOP1cc removal (TDP1, PNKP, and XRCC1) or in the resolution of R-loops (SETX) enhance DSB formation and prevent their repair. Such deficiencies cause neurological disorders. Owing to the high frequency of TOP1cc trapping and the widespread distribution of R-loops, these persistent transcriptional DSBs could accumulate over time in neuronal cells, contributing to the neurodegenerative diseases.
Insights
Transcription produces DNA double-strand breaks (DSBs) via two nearby single-strand breaks (SSBs) in resting cells. Defects in repairing these breaks contribute to neurodegenerative disorders.
Area of Science:
- Molecular Biology
- Genetics
- Neuroscience
Background:
- Genomic instability and DNA damage in resting cells are linked to neurodegenerative disorders.
- The mechanisms by which transcription generates DNA double-strand breaks (DSBs) in non-replicating cells are not fully understood.
Purpose of the Study:
- To elucidate the mechanism by which transcription leads to DNA double-strand breaks (DSBs) in non-replicating cells.
- To investigate the role of transcription-blocking topoisomerase I cleavage complexes (TOP1ccs) and R-loops in DSB formation.
Main Methods:
- Investigated the formation of DSBs from transcription-blocking TOP1ccs and R-loops.
- Utilized genetic approaches to study the impact of defects in TOP1cc removal and R-loop resolution pathways.
Main Results:
- DNA double-strand breaks (DSBs) arise from two adjacent single-strand breaks (SSBs) on opposite DNA strands.
- One SSB results from TOP1cc removal by the TDP1 pathway, the other from R-loop cleavage by endonucleases (XPF, XPG, FEN1).
- Genetic defects in TOP1cc removal (TDP1, PNKP, XRCC1) or R-loop resolution (SETX) exacerbate DSB formation and impair repair, leading to neurological disorders.
Conclusions:
- Persistent transcriptional DSBs, arising from TOP1ccs and R-loops, accumulate in neuronal cells.
- These accumulated DSBs contribute to the pathogenesis of neurodegenerative diseases.
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