Waters J C, Cole R W, Rieder C L
Wadsworth Center for Laboratories and Research, Albany, New York 12201-0509.
J Cell Biol. 1993 Jul;122(2):361-72. doi: 10.1083/jcb.122.2.361.
A popular hypothesis for centrosome separation during spindle formation and anaphase is that pushing forces are generated between interacting microtubules (MTs) of opposite polarity, derived from opposing centrosomes. However, this mechanism is not consistent with the observation that centrosomes in vertebrate cells continue to separate during prometaphase when their MT arrays no longer overlap (i.e., during anaphase-like prometaphase). To evaluate whether centrosome separation during prophase/prometaphase, anaphase-like prometaphase and anaphase is mediated by a common mechanism we compared their behavior in vivo at a high spatial and temporal resolution. We found that the two centrosomes possess a considerable degree of independence throughout all stages of separation, i.e., the direction and migration rate of one centrosome does not impart a predictable behavior to the other, and both exhibit frequent and rapid (4-6 microns/min) displacements toward random points within the cell including the other centrosome. The kinetic behavior of individual centrosomes as they separate to form the spindle is the same whether or not their MT arrays overlap. The characteristics examined include, e.g., total displacement per minute, the vectorial rate of motion toward and away from the other centrosome, the frequency of toward and away motion as well as motion not contributing to separation, and the rate contributed by each centrosome to the separation process. By contrast, when compared with prometaphase, anaphase centrosomes separated at significantly faster rates even though the average vectorial rate of motion away from the other centrosome was the same as in prophase/prometaphase. The difference in separation rates arises because anaphase centrosomes spend less time moving toward one another than in prophase/prometaphase, and at a significantly slower rate. From our data we conclude that the force for centrosome separation during vertebrate spindle formation is not produced by MT-MT interactions between opposing asters, i.e., that the mechanism is intrinsic to each aster. Our results also strongly support the contention that forces generated independently by each aster also contribute substantially to centrosome separation during anaphase, but that the process is modified by interactions between opposing astral MTs in the interzone.
关于纺锤体形成和后期中心体分离的一个流行假说是，在源自相对中心体的相反极性的相互作用微管（MTs）之间产生推力。然而，这一机制与以下观察结果不一致：脊椎动物细胞中的中心体在有丝分裂前期当它们的MT阵列不再重叠时（即，在类似后期的有丝分裂前期）仍继续分离。为了评估前期/有丝分裂前期、类似后期的有丝分裂前期和后期的中心体分离是否由共同机制介导，我们在高空间和时间分辨率下比较了它们在体内的行为。我们发现，在分离的所有阶段，两个中心体都具有相当程度的独立性，即一个中心体的方向和迁移速率不会赋予另一个中心体可预测的行为，并且两者都频繁且快速地（4 - 6微米/分钟）向细胞内的随机点位移，包括另一个中心体。单个中心体在分离形成纺锤体时的动力学行为，无论其MT阵列是否重叠都是相同的。所检查的特征包括，例如，每分钟的总位移、朝向和远离另一个中心体的矢量运动速率、朝向和远离运动以及不促进分离的运动的频率，以及每个中心体对分离过程的贡献速率。相比之下，与有丝分裂前期相比，后期中心体以明显更快的速率分离，尽管远离另一个中心体的平均矢量运动速率与前期/有丝分裂前期相同。分离速率的差异是因为后期中心体相互靠近移动的时间比前期/有丝分裂前期少，且速率明显更慢。从我们的数据中我们得出结论，脊椎动物纺锤体形成过程中中心体分离的力不是由相对星状体之间的MT - MT相互作用产生的，即该机制是每个星状体固有的。我们的结果也有力地支持了这样的观点，即每个星状体独立产生的力在后期也对中心体分离有很大贡献，但该过程会因中间区域相对星状MT之间的相互作用而改变。
