Further evidence for a random transition in the cell cycle

Abstract

SEVERAL proposals have been advanced to explain how cell cycle duration (and hence proliferation rates) is governed^1–3. It is important to establish which (if any) of these models is correct as they imply differing biological mechanisms of cell-cycle control. The transition probability hypothesis divides the cell cycle into two phases A and B, the transition from A to B occurring at random³. As a consequence a graph of the logarithm of the percentage of undivided cells (α_t) against time after mitosis (the α curve) shows two components since α_t will be 100% for times up to the minimum cycle time T_B (the duration of B phase) and decay exponentially thereafter. This model has been criticised on the grounds that other models of the cell cycle can generate similar α curves and on the basis of the α curve it is difficult to tell these models apart⁴. In what follows the exponential nature of the distribution of differences of sister cell cycle times (the β curve) is shown to be a unique property of cell cycle models containing an exponentially distributed phase.