An extended anaphase signaling pathway for Mad2p includes microtubule organizing center proteins and multiple motor-dependent transitions.
Signaling pathways within the mitotic mechanism temporally orchestrate spindle assembly with chromosome capture and alignment, and then coordinate initiation of chromosome segregation with spindle breakdown and cytokinesis for reproductive success. Kinetochore localized Mad2p acts in the spindle assembly checkpoint pathway during prophase and prometaphase to monitor bipolar attachment of chromosomes to spindle microtubules as well as proper tension at kinetochores. Once established, Mad2p is not degraded, but instead transits to spindle poles preceding the metaphase/anaphase transition in human and yeast cells. Whether conserved relocalization of Mad2p to poles is a final step in the spindle assembly checkpoint pathway or whether the post-metaphase transition allows Mad2p to cooperate in anaphase events leading to mitotic exit has been unknown. We examined post-metaphase localization of Mad2p in fission yeast. Our observations indicate an extended signaling pathway for Mad2p that includes kinetochore to bipolar localization at spindle poles, then additional transitions from bipolar to unipolar to equatorial. We determined that Mad2p associates with the microtubule organizing center complex through direct binding to Alp4p and that microtubule motor proteins Kinesin-14 Pkl1 and Dynein contribute to Mad2p anaphase transitions. At anaphase B onset, bipolar to unipolar transitions of both Mad2p and the septation inititiation network (SIN) kinase Cdc7 are observed. We determined that Mad2p and Cdc7p transitions monitor different events in anaphase, but that neither are required for anaphase B initiation. Our findings indicate that altered Mad2p anaphase spindle localizations can reflect changes in spindle function during mitotic exit that could contribute to fidelity in anaphase events.
Mayer
Christina
C
Biology Department, Boston College, Chestnut Hill, Massachusetts 02467, USA.
Filopei
Jason
J
Batac
Joe
J
Alford
Lea
L
Paluh
Janet L
JL
D000705:Anaphase; D018797:Cell Cycle Proteins / Q000235:genetics / Q000378:metabolism*; D016764:Cell Polarity; D048749:Cytokinesis; D004398:Dyneins / Q000378:metabolism; D016547:Kinesins / Q000378:metabolism; D064246:Mad2 Proteins; D022101:Microtubule-Organizing Center / Q000378:metabolism*; D009154:Mutation / Q000235:genetics; D009687:Nuclear Proteins / Q000235:genetics / Q000378:metabolism*; D011485:Protein Binding; D017346:Protein Serine-Threonine Kinases / Q000378:metabolism; D012568:Schizosaccharomyces / Q000166:cytology* / Q000235:genetics / Q000378:metabolism*; D029702:Schizosaccharomyces pombe Proteins / Q000235:genetics / Q000378:metabolism*; D015398:Signal Transduction; D014404:Tubulin / Q000378:metabolism
D018797:Cell Cycle Proteins; D064246:Mad2 Proteins; D009687:Nuclear Proteins; D029702:Schizosaccharomyces pombe Proteins; D014404:Tubulin; C577696:mad2 protein, S pombe; C068619:CDC7 protein, human; D017346:Protein Serine-Threonine Kinases; D004398:Dyneins; D016547:Kinesins