Nuclear actin polymerization rapidly mediates replication fork remodeling upon stress by limiting PrimPol activity

Area of Science:

• Cell Biology
• Molecular Biology
• Genetics

Background:

• Cells possess mechanisms to manage DNA replication stress, involving fork slowing and reversal.
• The role of nuclear organization, specifically nuclear actin, in replication fork plasticity remains unclear.

Purpose of the Study:

• To investigate the role of nuclear actin in regulating replication fork dynamics during genotoxic stress.
• To elucidate the molecular mechanisms by which nuclear actin influences DNA replication and genomic stability.

Main Methods:

• Utilized nuclear actin probes in live and fixed cells to visualize actin dynamics.
• Employed chemical and genetic methods to impair nuclear actin polymerization.
• Assessed replication fork progression, fork reversal, and the loading of key proteins like PrimPol, RAD51, and SMARCAL1.

Main Results:

• Nuclear actin filaments rapidly increase in number and length upon genotoxic treatment, contacting replication factories.
• Inhibition of nuclear actin polymerization prevents fork slowing and reversal.
• Defective actin polymerization leads to deregulated PrimPol loading, unrestrained DNA synthesis, and reduced RAD51/SMARCAL1 recruitment.
• Impaired nuclear actin polymerization causes chromosomal instability in a PrimPol-dependent manner.

Conclusions:

• Nuclear F-actin orchestrates replication fork plasticity by limiting PrimPol activity.
• Nuclear actin is a critical determinant in the cellular response to genotoxic stress and maintaining genomic integrity.