McDonald K L, Pfister K, Masuda H, Wordeman L, Staiger C, Cande W Z
Department of Botany, University of California, Berkeley 94720.
J Cell Sci Suppl. 1986;5:205-27. doi: 10.1242/jcs.1986.supplement_5.14.
The spindle in dividing cells of the diatom Stephanopyxis turris contains three distinct classes of microtubules: central spindle microtubules, which slide over each other and grow during anaphase spindle elongation; kinetochore-attached microtubules, which are located on the outer surface of the central spindle; and peripheral microtubules, which fan out from the spindle poles in astral-like arrays. The poles are multilayered structures, which remain attached to the spindle after isolation. In vitro, after addition of ATP, central spindles elongate and the two half-spindles slide completely apart with a concurrent decrease in the extent and magnitude of the zone of microtubule overlap. Spindle elongation takes place in spindles whose chromatin has been removed by enzymic digestion and the extent of elongation in vitro is increased by the addition of neurotubulin. After ATP addition the arrays of interdigitating microtubules in the zone of overlap become disordered and selectively depolymerize from the overlap zone polewards. In some reactivated spindles an unusual structure, a striated fibre, can be seen running from the pole plates part of the way towards the spindle midzone. The fibre has no precedent in mitotic ultrastructure and its function is unclear. These results demonstrate that we can duplicate the essential elements of anaphase B in vitro and that this system will be useful for further studies of the molecular basis of spindle elongation.
硅藻塔形冠盖藻（Stephanopyxis turris）分裂细胞中的纺锤体包含三类不同的微管：中央纺锤体微管，在后期纺锤体伸长过程中相互滑动并生长；着丝粒附着微管，位于中央纺锤体的外表面；以及外周微管，以星状排列从纺锤体极向外展开。纺锤体极是多层结构，分离后仍与纺锤体相连。在体外，加入ATP后，中央纺锤体伸长，两个半纺锤体完全滑开，同时微管重叠区域的范围和大小减小。纺锤体伸长发生在染色质已通过酶消化去除的纺锤体中，体外加入神经微管蛋白可增加伸长程度。加入ATP后，重叠区域中相互交错的微管阵列变得无序，并从重叠区域向极部选择性解聚。在一些重新激活的纺锤体中，可以看到一种不寻常的结构，即一条横纹纤维，从极板部分延伸至纺锤体中区。这种纤维在有丝分裂超微结构中没有先例，其功能尚不清楚。这些结果表明，我们可以在体外复制后期B的基本要素，并且该系统将有助于进一步研究纺锤体伸长的分子基础。
