Mitchison T J, Salmon E D
Department of Pharmacology, University of California, San Francisco 94143-0450.
J Cell Biol. 1992 Nov;119(3):569-82. doi: 10.1083/jcb.119.3.569.
Microtubules in the mitotic spindles of newt lung cells were marked using local photoactivation of fluorescence. The movement of marked segments on kinetochore fibers was tracked by digital fluorescence microscopy in metaphase and anaphase and compared to the rate of chromosome movement. In metaphase, kinetochore oscillations toward and away from the poles were coupled to kinetochore fiber shortening and growth. Marked zones on the kinetochore microtubules, meanwhile, moved slowly polewards at a rate of approximately 0.5 micron/min, which identifies a slow polewards movement, or "flux," of kinetochore microtubules accompanied by depolymerization at the pole, as previously found in PtK2 cells (Mitchison, 1989b). Marks were never seen moving away from the pole, indicating that growth of the kinetochore microtubules occurs only at their kinetochore ends. In anaphase, marked zones on kinetochore microtubules also moved polewards, though at a rate slower than overall kinetochore-to-pole movement. Early in anaphase-A, microtubule depolymerization at kinetochores accounted on average for 75% of the rate of chromosome-to-pole movement, and depolymerization at the pole accounted for 25%. When chromosome-to-pole movement slowed in late anaphase, the contribution of depolymerization at the kinetochores lessened, and flux became the dominant component in some cells. Over the whole course of anaphase-A, depolymerization at kinetochores accounted on average for 63% of kinetochore fiber shortening, and flux for 37%. In some anaphase cells up to 45% of shortening resulted from the action of flux. We conclude that kinetochore microtubules change length predominantly through polymerization and depolymerization at the kinetochores during both metaphase and anaphase as the kinetochores move away from and towards the poles. Depolymerization, though not polymerization, also occurs at the pole during metaphase and anaphase, so that flux contributes to polewards chromosome movements throughout mitosis. Poleward force production for chromosome movements is thus likely to be generated by at least two distinct molecular mechanisms.
利用荧光的局部光激活标记了蝾螈肺细胞有丝分裂纺锤体中的微管。通过数字荧光显微镜在中期和后期追踪动粒纤维上标记片段的运动，并与染色体运动速率进行比较。在中期，动粒向两极来回的振荡与动粒纤维的缩短和生长相关联。与此同时，动粒微管上的标记区域以大约0.5微米/分钟的速率缓慢向极移动，这确定了动粒微管存在缓慢的向极移动或“通量”，伴随着极处的解聚，正如先前在PtK2细胞中发现的那样（米奇森，1989b）。从未观察到标记从极处移开，这表明动粒微管的生长仅发生在其动粒末端。在后期，动粒微管上的标记区域也向极移动，不过其移动速率比动粒到极的整体移动速率要慢。在后期A的早期，动粒处微管的解聚平均占染色体向极移动速率的75%，极处的解聚占25%。当后期染色体向极移动减慢时，动粒处解聚的贡献减小，通量在一些细胞中成为主要成分。在后期A的整个过程中，动粒处的解聚平均占动粒纤维缩短的63%，通量占37%。在一些后期细胞中，高达45%的缩短是由通量的作用导致的。我们得出结论，在中期和后期，随着动粒远离和靠近两极，动粒微管主要通过动粒处的聚合和解聚来改变长度。在中期和后期，极处也会发生解聚，但不会发生聚合，因此通量在整个有丝分裂过程中都有助于染色体向极移动。因此，染色体运动的向极力产生可能是由至少两种不同的分子机制引起的。
