Cyclin-Dependent Kinase Sensor Transgenic Zebrafish Lines for Improved Cell Cycle State Visualization in Live Animals.

Adikes et al. 1 described a novel zebrafish cell cycle sensor that delineates all phases of the cell cycle based on levels of cyclin-dependent kinase (CDK) activity. The CDK sensor consists of a fragment of human DNA Helicase B (DHB) fused to a fluorescent protein. DHB contains a dominant nuclear localization sequence (NLS) and a nuclear export sequence (NES) flanked by CDK-specific phosphorylation sites. Cells that contain low levels of CDK activity have an exposed NLS that localizes the CDK sensor to the nucleus. As the cell cycle progresses, CDK activity increases causing phosphorylation of DHB, which occludes the NLS and allows the NES to promote export of the sensor into the cytoplasm (Fig. 1). The authors showed that quantitative analysis of this ratiometric sensor can distinguish CDK low (CDK), quiescent G0 arrested cells from CDK increasing (CDK), cycling G1 phase cells, as well as identify S, G2, and M phases of the cell cycle.