Dual regulation of Mad2 localization on kinetochores by Bub1 and Dam1/DASH that ensure proper spindle interaction.
The spindle assembly checkpoint monitors the state of spindle-kinetochore interaction to prevent premature onset of anaphase. Although checkpoint proteins, such as Mad2, are localized on kinetochores that do not interact properly with the spindle, it remains unknown how the checkpoint proteins recognize abnormalities in spindle-kinetochore interaction. Here, we report that Mad2 localization on kinetochores in fission yeast is regulated by two partially overlapping but distinct pathways: the Dam1/DASH and the Bub1 pathways. We show that Mad2 is localized on "unattached" as well as "tensionless" kinetochores. Our observations suggest that Bub1 is required for Mad2 to detect tensionless kinetochores, whereas Dam1/DASH is crucial for Mad2 to detect unattached kinetochores. In cells lacking both Bub1 and Dam1/DASH, Mad2 localization on kinetochores is diminished, and mitotic progression appears to be accelerated despite the frequent occurrence of abnormal chromosome segregation. Furthermore, we found that Dam1/DASH is required for promotion of spindle association with unattached kinetochores. In contrast, there is accumulating evidence that Bub1 is involved in resolution of erroneous spindle attachment on tensionless kinetochores. These pathways may act as molecular sensors determining the state of spindle association on each kinetochore, enabling proper regulation of the checkpoint activation as well as promotion/resolution of spindle attachment.
Saitoh
Shigeaki
S
Division of Cell Biology, Institute of Life Science, Kurume University, Kurume, Fukuoka 839-0864, Japan. saitoh@lsi.kurume-u.ac.jp
Kobayashi
Yasuyo
Y
Ogiyama
Yuki
Y
Takahashi
Kohta
K
D018797:Cell Cycle Proteins / Q000378:metabolism*; D002875:Chromosomes / Q000648:ultrastructure; D017353:Gene Deletion; D015971:Gene Expression Regulation, Enzymologic; D015966:Gene Expression Regulation, Fungal; D005838:Genotype; D049452:Green Fluorescent Proteins / Q000378:metabolism; D018386:Kinetochores / Q000378:metabolism*; D064246:Mad2 Proteins; D008856:Microscopy, Fluorescence / Q000379:methods; D008869:Microtubule-Associated Proteins / Q000378:metabolism*; D008938:Mitosis; D009687:Nuclear Proteins / Q000378:metabolism*; D010957:Plasmids / Q000378:metabolism; D017346:Protein Serine-Threonine Kinases / Q000378:metabolism*; D012568:Schizosaccharomyces / Q000235:genetics* / Q000502:physiology*; D029702:Schizosaccharomyces pombe Proteins / Q000378:metabolism*; D008941:Spindle Apparatus
D018797:Cell Cycle Proteins; C527984:Dam1 protein, S pombe; D064246:Mad2 Proteins; D008869:Microtubule-Associated Proteins; D009687:Nuclear Proteins; D029702:Schizosaccharomyces pombe Proteins; C577696:mad2 protein, S pombe; D049452:Green Fluorescent Proteins; C495594:Bub1 protein, S pombe; D017346:Protein Serine-Threonine Kinases