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Mismatch Repair01:36

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One of the common DNA damages is the chemical alteration of single bases by alkylation, oxidation, or deamination. The altered bases cause mispairing and strand breakage during replication. This type of damage causes minimal change to the DNA double helix structure and can be repaired by the base excision repair (BER) pathways. BER corrects damaged DNA sequences by removing the damaged base and restoring the original base sequence using the complementary strand as a template.
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The basic reaction of homologous recombination (HR) involves two chromatids that contain DNA sequences sharing a significant stretch of identity. One of these sequences uses a strand from another as a template to synthesize DNA in an enzyme-catalyzed reaction. The final product is a novel amalgamation of the two substrates. To ensure an accurate recombination of sequences, HR is restricted to the S and G2 phases of the cell cycle. At these stages, the DNA has been replicated already and the...
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Fine-Tuning Homology-Directed Repair (HDR) for Precision Genome Editing: Current Strategies and Future Directions.

Sibtain Haider1,2, Claudio Mussolino1,2,3

  • 1Institute for Transfusion Medicine and Gene Therapy, Medical Center-University of Freiburg, 79106 Freiburg, Germany.

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|May 14, 2025
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Summary

CRISPR-Cas9 genome editing faces challenges with precise DNA repair. Strategies are emerging to enhance homology-directed repair (HDR) over non-homologous end-joining (NHEJ) for accurate gene modification.

Keywords:
CRISPRCas9DNA repairHDRNHEJ

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CRISPR/Cas9-mediated Targeted Integration In Vivo Using a Homology-mediated End Joining-based Strategy
08:22

CRISPR/Cas9-mediated Targeted Integration In Vivo Using a Homology-mediated End Joining-based Strategy

Published on: March 12, 2018

Area of Science:

  • Molecular Biology
  • Genetics
  • Biotechnology

Background:

  • CRISPR-Cas9 enables targeted DNA cleavage, creating double-strand breaks (DSBs) for genome editing.
  • Non-homologous end-joining (NHEJ) is the dominant repair pathway, often causing disruptive insertions/deletions.
  • Homology-directed repair (HDR) allows precise gene editing but is less efficient than NHEJ, particularly in non-dividing cells.

Purpose of the Study:

  • To review recent advancements in enhancing homology-directed repair (HDR) efficiency for CRISPR-Cas9 genome editing.
  • To explore strategies for improving precise gene modification in various cell types.
  • To discuss the balance between NHEJ and HDR pathways for high-fidelity editing.

Main Methods:

  • Inhibition of non-homologous end-joining (NHEJ) pathway factors.
  • Optimization of donor DNA templates for homology-directed repair (HDR).
  • Cell cycle synchronization and engineering of HDR-enhancing fusion proteins.

Main Results:

  • Various methodologies show promise in boosting HDR efficiency compared to NHEJ.
  • Strategies aim to overcome limitations in postmitotic cells.
  • Advances facilitate more precise gene insertions, deletions, and substitutions.

Conclusions:

  • Manipulating the balance between NHEJ and HDR is crucial for advancing CRISPR-Cas9 applications.
  • Optimized strategies offer potential for high-fidelity genome editing in diverse cell types.
  • Further research is needed to fully realize the therapeutic and research potential of precise genome editing.