A mitosis-specific and R loop-driven ATR pathway promotes faithful chromosome segregation

Area of Science:

• Molecular Biology
• Cell Biology
• Genetics

Background:

• The ataxia telangiectasia mutated and Rad3-related (ATR) kinase is a key regulator of DNA damage and replication stress responses.
• ATR's role in DNA repair is well-established, but its function during mitosis remained largely unexplored.

Purpose of the Study:

• To investigate the unexpected role of ATR kinase during mitosis.
• To elucidate the molecular mechanisms by which ATR influences chromosome segregation.

Main Methods:

• Acute inhibition or degradation of ATR in mitotic cells.
• Analysis of chromosome missegregation, cyclin-dependent kinase 1 (CDK1) activity, DNA damage responses, and unscheduled DNA synthesis.
• Investigation of ATR localization at centromeres via association with centromere protein F (CENP-F) and its interaction with R loops.

Main Results:

• ATR inhibition or degradation during mitosis led to whole-chromosome missegregation.
• This effect was independent of CDK1 activity, DNA damage responses, or unscheduled DNA synthesis.
• ATR localizes to centromeres through Aurora A and CENP-F, engaging RPA-coated centromeric R loops to activate Aurora B via Chk1, thereby preventing lagging chromosomes.

Conclusions:

• A novel, mitosis-specific ATR pathway operates at centromeres, driven by R loops.
• This pathway is essential for faithful chromosome segregation by stimulating Aurora B and preventing lagging chromosomes.
• The study reveals critical functions of R loops and ATR in suppressing chromosome instability during cell division.