Mistimed origin licensing and activation stabilize common fragile sites under tight DNA-replication checkpoint...

Area of Science:

• Cell Biology
• Genetics
• Molecular Biology

Background:

• Genome integrity is crucial for cell division, requiring complete DNA replication before chromosome segregation.
• The DNA-replication checkpoint (DRC) coordinates replication and mitosis by inhibiting CDK1, delaying mitotic entry.
• Common fragile sites (CFSs) are prone to under-replication and breaks, often escaping DRC surveillance.

Purpose of the Study:

• To investigate if suboptimal DRC activation contributes to CFS under-replication and mitotic breaks.
• To determine the mechanisms by which DRC activation influences CFS stability and replication.

Main Methods:

• Utilized human cell models subjected to varying DRC activation levels.
• Employed Repli-Seq and molecular combing to analyze DNA replication initiation and timing.
• Investigated the roles of CDC6 and CDT1 in CFS replication and stability.

Main Results:

• Strengthening DRC activation or inhibiting CDK1 stabilized CFSs in human cells.
• A surge in replication initiations occurred in mid-S phase at late-replicating regions, including CFSs, without affecting the bulk genome.
• CFS stabilization and enhanced initiation depended on CDC6 and CDT1 availability, indicating mistimed origin licensing and firing due to CDK1 inhibition.

Conclusions:

• Tight DRC activation has a dual role: delaying mitosis and promoting replication completion in late-origin-poor domains.
• This enhanced replication support, particularly at CFSs, is critical for preventing under-replication and maintaining genome stability.
• CDK1 inhibition by the DRC allows for regulated, albeit mistimed, origin licensing and firing, safeguarding fragile genomic regions.