Mathematical model of the cell division cycle of fission yeast

Much is known about the genes and proteins controlling the cell cycle of fi ssion yeast. Can these molecular components be spun together into a consist ent mechanism that accounts for the observed behavior of growth and divisio n in fission yeast cells? To answer this question, we propose a mechanism f or the control system, convert it into a set of 14 differential and algebra ic equations, study these equations by numerical simulation and bifurcation theory, and compare our results to the physiology of wild-type and mutant cells. In wild-type cells, progress through the cell cycle (G1 -->S --> G2 -->M) is related to cyclic progression around a hysteresis loop, driven by cell growth and chromosome alignment on the metaphase plate. However, the c ontrol system operates much differently in double-mutant cells, wee1(-) cdc 25 Delta, which are defective in progress through the latter half of the ce ll cycle (G2 and M phases). These cells exhibit "quantized" cycles (interdi vision times clustering around 90, 160, and 230 min). We show that these qu antized cycles are associated with a supercritical Hopf bifurcation in the mechanism, when the wee1 and cdc25 genes are disabled. (C) 2001 American In stitute of Physics.