Progressive activation of CyclinB1-Cdk1 coordinates entry to mitosis.
The CyclinB1-Cdk1 kinase is the catalytic activity at the heart of mitosis-promoting factor (MPF), yet fundamental questions concerning its role in mitosis remained unresolved. It is not known when and how rapidly CyclinB1-Cdk1 is activated in mammalian cells, nor how its activation coordinates the substantial changes in the cell at mitosis. Here, we have developed a FRET biosensor specific for CyclinB1-Cdk1 that enables us to assay its activity with very high temporal precision in living human cells. We show that CyclinB1-Cdk1 is inactive in G2 phase and activated at a set time before nuclear envelope breakdown, thereby initiating the events of prophase. CyclinB1-Cdk1 levels rise to their maximum extent over the course of approximately 30 min, and we demonstrate that different levels of CyclinB1-Cdk1 kinase activity trigger different mitotic events, thus revealing how the remarkable reorganization of the cell is coordinated at mitotic entry.
Gavet
Olivier
O
The Gurdon Institute and Department of Zoology, Tennis Court Road, CB2 1QN Cambridge, UK. ocg21@cam.ac.uk
Pines
Jonathon
J
D000705:Anaphase; D015374:Biosensing Techniques; D016203:CDC2 Protein Kinase / Q000378:metabolism*; D002453:Cell Cycle; D002460:Cell Line; D056744:Cyclin B1 / Q000378:metabolism*; D031541:Fluorescence Resonance Energy Transfer; D016195:G2 Phase; D006801:Humans; D008938:Mitosis; D008954:Models, Biological; D009685:Nuclear Envelope / Q000378:metabolism; D013997:Time Factors; D014162:Transfection
D056744:Cyclin B1; D016203:CDC2 Protein Kinase