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Updated: Jun 29, 2025

Two- and Three-Dimensional Live Cell Imaging of DNA Damage Response Proteins
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Published on: September 28, 2012

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Spatial organization and functions of Chk1 activation by TopBP1 biomolecular condensates

Tom Egger1, Laura Morano1, Marie-Pierre Blanchard2

  • 1Institut de Génétique Humaine, Université de Montpellier, CNRS, Montpellier, France.

Cell Reports
|April 5, 2024
PubMed

Insights

TopBP1 condensates activate the ATR/Chk1 pathway crucial for DNA replication repair. Specific motifs in TopBP1

Area of Science:

  • Cell Biology
  • Molecular Biology
  • Genetics

Background:

  • The ataxia telangiectasia-mutated and Rad3-related (ATR)/Chk1 signaling pathway is vital for coordinating cellular responses to DNA replication stress.
  • TopBP1 biomolecular condensates are known to trigger the activation of this pathway.

Purpose of the Study:

  • To investigate the role of sequence-specific motifs in the formation and function of TopBP1 condensates using optogenetics and reverse genetics.
  • To explore the involvement of BACH1/FANCJ in BRCA1 partitioning within TopBP1 compartments.

Main Methods:

  • Optogenetics and reverse genetics were employed to study TopBP1 condensate formation and function.
  • Analysis of Chk1 phosphorylation dependence on specific TopBP1 motifs.
  • Investigation of cell cycle checkpoint activation and replication fork dynamics.

Main Results:

  • Chk1 activation occurs at the interface of TopBP1 condensates, which form at DNA damage sites in human fibroblasts.
  • Chk1 phosphorylation is dependent on a conserved arginine motif in TopBP1's ATR activation domain (AAD).
  • Mutation of this motif uncouples Chk1 activation from condensation, and optogenetically induced Chk1 phosphorylation triggers checkpoints and slows replication forks without DNA damage.

Conclusions:

  • The intrinsically disordered AAD of TopBP1 encodes distinct molecular steps in the ATR/Chk1 pathway.
  • TopBP1 condensates and their associated motifs play a critical role in regulating DNA replication and cell cycle checkpoints.
Keywords:
ATR/Chk1 signaling pathwayCP: Molecular biologyDNA damage responseDNA replication stressbiomolecular condensatesoptogenetics

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