Overview

• Advanced biosensors show CDK activation peaks in the nucleus before any activity appears in the cytoplasm.
• Nuclear CDK activation requires higher cyclin levels to coordinate DNA replication and damage monitoring.
• Localization of cyclin-CDK complexes to the spindle pole body is unnecessary for initial activation but essential for their export and cytoplasmic signaling.
• Preventing cyclin export to the cytoplasm halts mitotic entry outside the nucleus, confirming a two-step activation process.
• These findings refine models of mitotic control and highlight potential targets for studies on genomic stability and cancer biology.