Intrinsic checkpoint deficiency during cell cycle re-entry from quiescence

Area of Science:

• Cell Biology
• Molecular Biology
• Genetics

Background:

• Cellular homeostasis relies on transitions between quiescence and proliferation.
• Origin licensing, involving minichromosome maintenance complex (MCM) loading, is crucial for DNA replication initiation.
• A p53-dependent checkpoint normally ensures adequate MCM loading before S phase entry.

Purpose of the Study:

• To compare MCM loading and origin licensing efficiency during the first G1 phase after cell cycle re-entry versus subsequent G1 phases.
• To investigate the impact of underlicensing on cellular response to replication stress.
• To determine if repeated quiescence cycles exacerbate replication stress sensitivity.

Main Methods:

• Quantitative flow cytometry
• Live cell imaging
• Cell cycle analysis

Main Results:

• The first G1 phase after cell cycle re-entry is significantly underlicensed for DNA replication origins, despite being longer.
• Cells in the first S phase exhibit hypersensitivity to replication stress due to slow MCM loading and a compromised licensing checkpoint.
• Hypersensitivity to replication stress intensifies with repeated rounds of quiescence.

Conclusions:

• Underlicensing during the first cell cycle post-quiescence creates a high-risk period for genome instability.
• Impaired origin licensing and checkpoint function contribute to replication stress sensitivity.
• Repeated quiescence may progressively compromise DNA replication fidelity.