Cell cycle synchronization in early Drosophila embryos
Early embryogenesis of most metazoans is characterized by rapid and synchronous cleavage divisions. While diffusion is too slow for synchronization of mitosis across large spatial scales, traveling waves represent a possible process of synchronization. I will discuss our recent work dissecting the molecular and physical mechanisms for the generation of traveling waves of activity of Cdk1, the master regulator of the cell cycle. I will show that the in vivo dynamics of Cdk1 are captured by a transiently bistable reaction-diffusion model, where time-dependent reaction terms account for the growing level of cyclins and Cdk1 activation across the cell cycle. I will discuss two distinct regimes. The first one is observed in mutants of the mitotic switch. There, waves are triggered by the classical mechanism of a stable state invading a metastable one. Conversely, waves in wild type reflect a transient phase that preserves the Cdk1 spatial gradients while the overall level of Cdk1 activity is swept upward by the time-dependent reaction terms. This unique mechanism generates a wave-like spreading (sweep-waves) that differs from bistable waves for its dependence on dynamic parameters and its faster speed. I will also discuss how the integration of biochemical and mechanical processes is required for the early establishment of synchronization of the cell cycle.