Kapoor T M, Mayer T U, Coughlin M L, Mitchison T J
Department of Cell Biology, Harvard Medical School, Boston, Massachusetts 02115, USA.
J Cell Biol. 2000 Sep 4;150(5):975-88. doi: 10.1083/jcb.150.5.975.
Monastrol, a cell-permeable small molecule inhibitor of the mitotic kinesin, Eg5, arrests cells in mitosis with monoastral spindles. Here, we use monastrol to probe mitotic mechanisms. We find that monastrol does not inhibit progression through S and G2 phases of the cell cycle or centrosome duplication. The mitotic arrest due to monastrol is also rapidly reversible. Chromosomes in monastrol-treated cells frequently have both sister kinetochores attached to microtubules extending to the center of the monoaster (syntelic orientation). Mitotic arrest-deficient protein 2 (Mad2) localizes to a subset of kinetochores, suggesting the activation of the spindle assembly checkpoint in these cells. Mad2 localizes to some kinetochores that have attached microtubules in monastrol-treated cells, indicating that kinetochore microtubule attachment alone may not satisfy the spindle assembly checkpoint. Monastrol also inhibits bipolar spindle formation in Xenopus egg extracts. However, it does not prevent the targeting of Eg5 to the monoastral spindles that form. Imaging bipolar spindles disassembling in the presence of monastrol allowed direct observations of outward directed forces in the spindle, orthogonal to the pole-to-pole axis. Monastrol is thus a useful tool to study mitotic processes, detection and correction of chromosome malorientation, and contributions of Eg5 to spindle assembly and maintenance.
莫那可林（Monastrol）是一种可透过细胞的小分子有丝分裂驱动蛋白Eg5抑制剂，它能使细胞停滞在有丝分裂期并形成单星体纺锤体。在此，我们使用莫那可林来探究有丝分裂机制。我们发现莫那可林并不抑制细胞周期S期和G2期的进程或中心体复制。由莫那可林导致的有丝分裂停滞也是快速可逆的。用莫那可林处理的细胞中的染色体，其两条姐妹动粒常常都附着于延伸至单星体中心的微管上（着丝粒定向）。有丝分裂停滞缺陷蛋白2（Mad2）定位于一部分动粒上，这表明这些细胞中的纺锤体组装检查点被激活。在经莫那可林处理的细胞中，Mad2定位于一些已附着微管的动粒上，这表明仅动粒微管附着可能无法满足纺锤体组装检查点的要求。莫那可林还能抑制非洲爪蟾卵提取物中双极纺锤体的形成。然而，它并不阻止Eg5靶向所形成的单星体纺锤体。在莫那可林存在的情况下对双极纺锤体解体进行成像，可直接观察到纺锤体中与两极轴垂直的向外作用力。因此，莫那可林是研究有丝分裂过程、染色体错误定向的检测与校正以及Eg5对纺锤体组装和维持的作用的有用工具。
