Dynamical mechanisms underlying distinct G1-phase decisions.

<p>(A) Schematic representation of how the signal modifies the trajectories of G1-phase progression in the state space in the case of reversible (left panels) and irreversible (right panels) G1-arrest states. Black circles and white circles indicate a stable equilibrium linked to a G1-arrest state and an unstable equilibrium, respectively. Half black and half white circle indicates a saddle-node equilibrium. Left and right panels correspond to two qualitatively distinct scenarios. In case of limit cycle trajectories (connecting S to M), panels (a) and (b) would correspond to a saddle-node bifurcation on invariant cycle and a saddle homoclinic bifurcation, respectively. (B) Typical asymptotic relationship between the rate of G1-phase progression () and strength associated with reversible and irreversible G1-arrest scenarios (see supporting material).