title: Timing and checkpoints in the regulation of mitotic progression.
abstract: Accurate chromosome segregation relies on the precise regulation of mitotic progression. Regulation involves control over the timing of mitosis and a spindle assembly checkpoint that links anaphase onset to the completion of chromosome-microtubule attachment. In this paper, we combine live-cell imaging of HeLa cells and protein depletion by RNA interference to examine the functions of the Mad, Bub, and kinetochore proteins in mitotic timing and checkpoint control. We show that the depletion of any one of these proteins abolishes the mitotic arrest provoked by depolymerizing microtubules or blocking chromosome-microtubule attachment with RNAi. However, the normal progress of mitosis is accelerated only when Mad2 or BubR1, but not other Mad and Bub proteins, are inactivated. Moreover, whereas checkpoint control requires kinetochores, the regulation of mitotic timing by Mad2 and BubR1 is kinetochore-independent in fashion. We propose that cytosolic Mad2-BubR1 is essential to restrain anaphase onset early in mitosis when kinetochores are still assembling.
authors.affiliation: Department of Biology, Massachusetts Institute of Technology, Cambridge, MA 02139, USA.
authors.forename: Patrick
authors.initials: P
authors.lastname: Meraldi
authors.forename: Viji M
authors.initials: VM
authors.lastname: Draviam
authors.forename: Peter K
authors.initials: PK
authors.lastname: Sorger
mesh_terms: D000705:Anaphase / Q000502:physiology; D002352:Carrier Proteins / Q000235:genetics / Q000378:metabolism*; D018797:Cell Cycle Proteins / Q000235:genetics*; D003598:Cytoskeletal Proteins; D003600:Cytosol / Q000378:metabolism; D018816:Genes, cdc / Q000502:physiology*; D006367:HeLa Cells; D006801:Humans; D018386:Kinetochores / Q000378:metabolism; D008870:Microtubules / Q000378:metabolism; D008938:Mitosis / Q000235:genetics*; D009687:Nuclear Proteins / Q000378:metabolism; D010641:Phenotype; D010750:Phosphoproteins / Q000235:genetics / Q000378:metabolism; D011494:Protein Kinases / Q000172:deficiency* / Q000235:genetics; D017346:Protein Serine-Threonine Kinases; D034622:RNA Interference; D012097:Repressor Proteins / Q000235:genetics / Q000378:metabolism; D008941:Spindle Apparatus / Q000378:metabolism*
chemical_list: D002352:Carrier Proteins; D018797:Cell Cycle Proteins; D003598:Cytoskeletal Proteins; C501384:MAD1L1 protein, human; C120529:NDC80 protein, human; C490197:NUF2 protein, human; D009687:Nuclear Proteins; D010750:Phosphoproteins; D012097:Repressor Proteins; D011494:Protein Kinases; C584277:BUB1 protein, human; C090464:Bub1 spindle checkpoint protein; D017346:Protein Serine-Threonine Kinases