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MBC in Press, published online ahead of print July 16, 2008
Mol. Biol. Cell 10.1091/mbc.E08-03-0298

A more recent version of this article appeared on September 1, 2008
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Submitted on March 19, 2008
Revised on July 2, 2008
Accepted on July 2, 2008

Dual Regulation of Mad2 Localization on Kinetochores by Bub1 and Dam1/DASH that Ensure Proper Spindle Interaction

Shigeaki Saitoh, Yasuyo Kobayashi,* Yuki Ogiyama, and Kohta Takahashi

Division of Cell Biology, Institute of Life Science, Kurume University, Kurume Research Center Bld., 1–1 Hyakunen-kohen, Kurume, Fukuoka 839-0864, Japan, Tel: +81–942-37–6317, Fax:+81–942-31–3320

Monitoring Editor: Kerry S. Bloom

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, while 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.

*Present address: KAN Research Institute, Inc., Kobe MI R&D Center, 6–7-3 Minatojima-minamimachi, Chuo-ku, Kobe 650-0047, Japan.

Address correspondence to: Shigeaki Saitoh (saitoh{at}lsi.kurume-u.ac.jp) or Kohta Takahashi (takahash{at}lsi.kurume-u.ac.jp)






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