Abstract
While feedback loops are essential for robustness in signaling systems, they make discerning the role of individual components challenging. Here we introduce temperature as a powerful perturbation method for uncoupling enzymatic processes, by exposing the differential sensitivity of limiting reactions to temperature due to their activation energies. Using this method, we study the sensitivity to temperature of different cell cycle events of early fly embryos. While the subdivision of cell cycle steps is conserved across a wide range of temperatures (5-35°C), the transition into prometaphase exhibits the most sensitivity, arguing that it has a different mechanism of regulation. Using a biosensor, we quantify the activity of Cdk1 and show that the activation of Cdk1 drives entry into prometaphase but is not required for earlier events. In fact, chromosome condensation can still occur when Cdk1 is inhibited pharmacologically. These results demonstrate that different kinases are rate-limiting for different steps of mitosis.
