Cyclin B1-Cdk1 activation continues after centrosome separation to control mitotic progression

Area of Science:

• Cell Biology
• Molecular Biology
• Biochemistry

Background:

• Mitotic entry is driven by cyclin B1-cyclin-dependent kinase 1 (Cdk1) activation via a positive feedback loop.
• Mitotic exit involves cyclin B1 destruction, inactivating Cdk1.
• Experimental data on Cdk1 activation kinetics within mitotic cells are scarce.

Purpose of the Study:

• To experimentally determine the temporal dynamics of cyclin B1-Cdk1 activity in single human cells during mitosis.
• To investigate the mechanisms regulating Cdk1 activity post-centrosome separation.
• To model Cdk1 activation kinetics and compare it with existing theoretical frameworks.

Main Methods:

• Utilized a novel approach to quantify Cdk1 dephosphorylation and phosphorylation of its target, anaphase-promoting complex/cyclosome 3.
• Measured cyclin B1-Cdk1 activity in single cells throughout mitosis.
• Developed a mathematical model to fit experimental data.

Main Results:

• Disclosed that cyclin B1-Cdk1 activity continues to increase after centrosome separation.
• Demonstrated that cytoplasmic cyclin B1-Cdk1 activity persists even when cyclin B1 localizes to the nucleus.
• The experimental data fit a model exhibiting bistable circuit characteristics.

Conclusions:

• Cyclin B1-Cdk1 activation kinetics in human cells resemble a bistable circuit.
• Different thresholds of cyclin B1-Cdk1 activity are required for mitotic entry versus progression.
• Gradual increases in cyclin B1-Cdk1 activity post-centrosome separation are vital for coordinating mitotic progression.