Bifurcation analysis of bistability in the mitotic checkpoint network.

From left to right, bifurcation diagram for three consecutive moments of the experiment simulated in Fig 1D. At the beginning of the experiment (left), cells are in the checkpoint OFF state, arrested in anaphase (by the <i>cdc15-2</i> mutation). Although all kinetochores are attached, on the x-axis the checkpoint activating signal is not zero due to the lack of tension between sister chromatids. When Mps1 is overexpressed (middle), the checkpoint OFF state is greatly reduced, and the system is attracted to the only available steady state, checkpoint ON. After the overexpression stops (right), the original checkpoint OFF steady state is available again. Yet, cells remain attracted to the checkpoint ON steady state. (PDF)