cyclin b1–cdk1 activation continues after centrosome separation to control mitotic progression细胞周期蛋白b1-cdk1激活后继续中心体分离控制有丝分裂进程.pdfVIP

PLoS BIOLOGY Cyclin B1–Cdk1 Activation Continues after Centrosome Separation to Control Mitotic Progression 1¤* 2 1 2 Arne Lindqvist , Wouter van Zon , Christina Karlsson Rosenthal , Rob M. F. Wolthuis 1 Department of Cell and Molecular Biology, Karolinska Institutet, Stockholm, Sweden, 2 Division of Molecular Biology/P2, The Netherlands Cancer Institute, Amsterdam, The Netherlands Activation of cyclin B1–cyclin-dependent kinase 1 (Cdk1), triggered by a positive feedback loop at the end of G2, is the key event that initiates mitotic entry. In metaphase, anaphase-promoting complex/cyclosome–dependent destruction of cyclin B1 inactivates Cdk1 again, allowing mitotic exit and cell division. Several models describe Cdk1 activation kinetics in mitosis, but experimental data on how the activation proceeds in mitotic cells have largely been lacking. We use a novel approach to determine the temporal development of cyclin B1–Cdk1 activity in single cells. By quantifying both dephosphorylation of Cdk1 and phosphorylation of the Cdk1 target anaphase-promoting complex/cyclosome 3, we disclose how cyclin B1–Cdk1 continues to be activated after centrosome separation. Importantly, we discovered that cytoplasmic cyclin B1–Cdk1 activity can be maintained even when cyclin B1 translocates to the nucleus in prophase. These experimental data are fitted into a model describing cyclin B1–Cdk1 activation in human cells, revealing a striking resemblance to a bistable circuit. In line with the observed kinetics, cyclin B1–Cdk1 levels required to enter mitosis are lower than the amount of cyclin B1–Cdk1 needed for mitotic progression. We propose that graduall