Ras-dependent cell cycle commitment during G2 phase

Synchronization used to study cell cycle progression may change the charact eristics of rapidly proliferating cells. By combining time-lapse, quantitat ive fluorescent microscopy and microinjection, we have established a method to analyze the cell cycle progression of individual cells without synchron ization. This new approach revealed that rapidly growing NIH3T3 cells make a Ras-dependent commitment for completion of the next fell cycle while they are in G2 phase of the preceding cell cycle. Thus, Ras activity during G2 phase induces cyclin D1 expression. This expression continues through the n ext G1 phase even in the absence of Ras activity and drives cells into S ph ase. (C) 2001 Federation of European Biochemical Societies. Published by El sevier Science B.V. All rights reserved.