title: Probing spindle assembly mechanisms with monastrol, a small molecule inhibitor of the mitotic kinesin, Eg5.
abstract: 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.
authors.affiliation: Department of Cell Biology, Harvard Medical School, Boston, Massachusetts 02115, USA. tarun_kapoor@hms.harvard.edu
authors.forename: T M
authors.initials: TM
authors.lastname: Kapoor
authors.forename: T U
authors.initials: TU
authors.lastname: Mayer
authors.forename: M L
authors.initials: ML
authors.lastname: Coughlin
authors.forename: T J
authors.initials: TJ
authors.lastname: Mitchison
mesh_terms: D000818:Animals; D000970:Antineoplastic Agents / Q000494:pharmacology; D002135:Calcium-Binding Proteins / Q000502:physiology; D002352:Carrier Proteins; D002453:Cell Cycle / Q000187:drug effects / Q000502:physiology*; D018797:Cell Cycle Proteins; D002460:Cell Line; D002474:Cell-Free System; D018385:Centrosome / Q000187:drug effects / Q000502:physiology*; D002875:Chromosomes / Q000187:drug effects / Q000502:physiology / Q000648:ultrastructure; D005656:Fungal Proteins / Q000502:physiology; D016547:Kinesins / Q000037:antagonists & inhibitors / Q000502:physiology*; D008870:Microtubules / Q000502:physiology* / Q000648:ultrastructure; D008938:Mitosis / Q000187:drug effects / Q000502:physiology*; D009687:Nuclear Proteins; D009865:Oocytes / Q000502:physiology; D011743:Pyrimidines / Q000494:pharmacology*; D008941:Spindle Apparatus / Q000502:physiology* / Q000648:ultrastructure; D013871:Thiones / Q000494:pharmacology*; D029867:Xenopus Proteins; D014982:Xenopus laevis
chemical_list: D000970:Antineoplastic Agents; D002135:Calcium-Binding Proteins; D002352:Carrier Proteins; D018797:Cell Cycle Proteins; D005656:Fungal Proteins; C088335:KIF11 protein, Xenopus; D009687:Nuclear Proteins; D011743:Pyrimidines; D013871:Thiones; D029867:Xenopus Proteins; C400223:monastrol; D016547:Kinesins