Capturing CDKs in action: Live-cell biosensors pioneer the new frontiers in cell cycle research

Cyclin-dependent kinases (CDKs) orchestrate cell cycle progression through precise temporal control of substrate phosphorylation. While traditional biochemical approaches and phosphoproteomics have provided valuable insights into CDK-mediated regulation, these methods require cell population analyses and cannot capture real-time dynamics in individual cells. The recent development of fluorescent biosensors has revolutionized our ability to monitor CDK activity in living cells with unprecedented temporal and spatial resolution. Here, we comprehensively review genetically encoded fluorescent biosensors for measuring CDK activity. The two major modes of action in CDK activity biosensors-FRET-based and translocation-based biosensors-enable researchers to select appropriate tools for their specific experimental objectives. These biosensors have revealed precise spatiotemporal CDK activity dynamics across diverse model systems, including yeast, cultured mammalian cells, worms, flies, frog egg extract, fish, and mice. Such technological advances are transforming our understanding of quantitative principles underlying cell cycle control and opening new avenues for investigating cell cycle regulation in various biological contexts.Key words: CDK, FRET, cell cycle, live imaging, biosensor.