The molecular architecture of cell cycle arrest

The cellular decision governing the transition between proliferative and arrested states is crucial to the development and function of every tissue. While the molecular mechanisms that regulate the proliferative cell cycle are well established, we know comparatively little about what happens to cells as they diverge into cell cycle arrest. We combined hyperplexed, single-cell imaging with manifold learning to obtain a map of the molecular architecture that governs cell cycle exit and progression into reversible (“quiescent”) and irreversible (“senescent”) states of arrest. Using this map, we resolved multiple points of divergence from the proliferative cell cycle into distinct states of arrest and the molecular mechanisms governing these fate decisions, which we verified by single-cell, time-lapse imaging. We found that senescence is an obligate G1-like molecular state, regardless of the phase of cell cycle exit, and that cells can escape from this “irreversible” state of arrest through the upregulation of G1 – but not G2 – cyclins. This map of cell cycle arrest provides our first glimpse of the overall organization of the proliferation/arrest decision.