Verde F, Dogterom M, Stelzer E, Karsenti E, Leibler S
EMBL, Heidelberg, Germany.
J Cell Biol. 1992 Sep;118(5):1097-108. doi: 10.1083/jcb.118.5.1097.
In eukaryotic cells, the onset of mitosis involves cyclin molecules which interact with proteins of the cdc2 family to produce active kinases. In vertebrate cells, cyclin A dependent kinases become active in S- and pro-phases, whereas a cyclin B-dependent kinase is mostly active in metaphase. It has recently been shown that, when added to Xenopus egg extracts, bacterially produced A- and B-type cyclins associate predominantly with the same kinase catalytic subunit, namely p34cdc2, and induce its histone H1 kinase activity with different kinetics. Here, we show that in the same cell free system, both the addition of cyclin A and cyclin B changes microtubule behavior. However, the cyclin A-dependent kinase does not induce a dramatic shortening of centrosome-nucleated microtubules whereas the cyclin B-dependent kinase does, as previously reported. Analysis of the parameters of microtubule dynamics by fluorescence video microscopy shows that the dramatic shortening induced by the cyclin B-dependent kinase is correlated with a several fold increase in catastrophe frequency, an effect not observed with the cyclin A-dependent kinase. Using a simple mathematical model, we show how the length distributions of centrosome-nucleated microtubules relate to the four parameters that describe microtubule dynamics. These four parameters define a threshold between unlimited microtubule growth and the establishment of steady-state dynamics, which implies that well defined steady-state length distributions can be produced by regulating precisely the respective values of the dynamical parameters. Moreover, the dynamical model predicts that increasing catastrophe frequency is more efficient than decreasing the rescue frequency to reduce the average steady state length of microtubules. These theoretical results are quantitatively confirmed by the experimental data.
在真核细胞中，有丝分裂的开始涉及细胞周期蛋白分子，这些分子与细胞分裂周期蛋白2（cdc2）家族的蛋白质相互作用以产生活性激酶。在脊椎动物细胞中，细胞周期蛋白A依赖性激酶在S期和前期变得活跃，而细胞周期蛋白B依赖性激酶大多在中期活跃。最近有研究表明，当将细菌产生的A 型和B型细胞周期蛋白添加到非洲爪蟾卵提取物中时，它们主要与同一激酶催化亚基，即p34cdc2结合，并以不同的动力学诱导其组蛋白H1激酶活性。在此，我们表明在同一无细胞体系中，添加细胞周期蛋白A和细胞周期蛋白B都会改变微管行为。然而，细胞周期蛋白A依赖性激酶不会诱导中心体成核微管的显著缩短，而细胞周期蛋白B依赖性激酶则会，这与之前报道的一致。通过荧光视频显微镜对微管动力学参数的分析表明，细胞周期蛋白B依赖性激酶诱导的显著缩短与灾难频率增加几倍相关，而细胞周期蛋白A依赖性激酶未观察到这种效应。使用一个简单的数学模型，我们展示了中心体成核微管的长度分布如何与描述微管动力学的四个参数相关。这四个参数定义了微管无限生长与建立稳态动力学之间的阈值，这意味着通过精确调节动力学参数的各自值可以产生明确的稳态长度分布。此外，动力学模型预测，增加灾难频率比降低拯救频率更有效地减少微管的平均稳态长度。这些理论结果得到了实验数据的定量证实。
