A G1 rate model accounts for cell-cycle kinetics attributed to ‘transition probability’

Abstract

Smith and his colleagues have proposed that the duration of the cell cycle is determined by a random transition, analogous to the random decay of a radioactive nucleus, by which a cell passes from an A state within the G1 phase to a B phase that includes the rest of the cycle. The experimental support for this transition probability hypothesis is the tendency of a cumulative plot of differences of cycle times of sibling cells (the .beta. curve) to be exponential and parallel to the exponential tail of a cumulative plot of the cycle times themselves (the .alpha. curve). A close examination of 4 of the most extensive sets of experimental data suggests that the 2 .beta. curves with the steepest slopes may not, in fact, be exponential. These and all the other characteristics of the experimental curves are best matched by computer simulations using a cell-cycle model that will be termed here a G1 rate model. This model is consistent with differences in cell metabolism, rather than a transition at an inherently unpredictable time, being the physiological basis for differences in cycle times within a cell population.