McNally F J, Thomas S
Section of Molecular and Cellular Biology, University of California, Davis, Davis, California 95616, USA.
Mol Biol Cell. 1998 Jul;9(7):1847-61. doi: 10.1091/mbc.9.7.1847.
Microtubules are dynamic structures whose proper rearrangement during the cell cycle is essential for the positioning of membranes during interphase and for chromosome segregation during mitosis. The previous discovery of a cyclin B/cdc2-activated microtubule-severing activity in M-phase Xenopus egg extracts suggested that a microtubule-severing protein might play an important role in cell cycle-dependent changes in microtubule dynamics and organization. However, the isolation of three different microtubule-severing proteins, p56, EF1alpha, and katanin, has only confused the issue because none of these proteins is directly activated by cyclin B/cdc2. Here we use immunodepletion with antibodies specific for a vertebrate katanin homologue to demonstrate that katanin is responsible for the majority of M-phase severing activity in Xenopus eggs. This result suggests that katanin is responsible for changes in microtubules occurring at mitosis. Immunofluorescence analysis demonstrated that katanin is concentrated at a microtubule-dependent structure at mitotic spindle poles in Xenopus A6 cells and in human fibroblasts, suggesting a specific role in microtubule disassembly at spindle poles. Surprisingly, katanin was also found in adult mouse brain, indicating that katanin may have other functions distinct from its mitotic role.
微管是动态结构，其在细胞周期中的正确重排对于间期膜的定位和有丝分裂期间染色体的分离至关重要。先前在M期非洲爪蟾卵提取物中发现细胞周期蛋白B/cdc2激活的微管切断活性，这表明一种微管切断蛋白可能在微管动力学和组织的细胞周期依赖性变化中起重要作用。然而，三种不同的微管切断蛋白p56、EF1α和katanin的分离却使问题变得更加复杂，因为这些蛋白均不能被细胞周期蛋白B/cdc2直接激活。在这里，我们使用针对脊椎动物katanin同源物的特异性抗体进行免疫去除实验，以证明katanin负责非洲爪蟾卵中大部分M期切断活性。这一结果表明katanin与有丝分裂时微管的变化有关。免疫荧光分析表明，katanin集中在非洲爪蟾A6细胞和人类成纤维细胞有丝分裂纺锤体极的微管依赖性结构上，这表明它在纺锤体极微管解聚中具有特定作用。令人惊讶的是，在成年小鼠大脑中也发现了katanin，这表明katanin可能具有与其有丝分裂作用不同的其他功能。
