第23回先端研究セミナーのお知らせ

演題：How chromosomes regulate mitosis

演者：横山 英樹（Zentrum für Molekulare Biologie der Universität Heidelberg (ZMBH)）

抄録：In mitosis, chromosomes are not simply passengers segregated by spindle microtubules. They actively drive spindle assembly by producing the GTP bound form of the Ran GTPase in their vicinity [1]. Ran-GTP binds to the heterodimeric nuclear transport receptor importin a/b and dissociates nuclear localization signal (NLS)-containing proteins from the importins [2]. Liberated NLS proteins, such as TPX2, have been thought to play distinct roles in spindle microtubule assembly. To comprehensively identify novel Ran-regulated spindle assembly factors, I sequentially purified NLS proteins and microtubule-associated proteins (MAPs) from Xenopus egg extracts, and identified ~170 proteins [3, 4]. Of those, the chromatin-remodeling ATPases, CHD4 and ISWI, surprisingly function as bona-fide MAPs. Both proteins dissociate from chromatin in mitosis and re-localize to the spindle. They play roles, however, in distinct mitotic stages: CHD4 is a Ran-GTP dependent microtubule stabilizer essential for spindle assembly during early stages of mitosis [4], while ISWI specifically stabilizes microtubules in anaphase to maintain the spindle during chromosome segregation [5]. The functions of CHD4 and ISWI are independent of chromatin remodeling, and are conserved in Xenopus egg extracts and human cells. My data establish a new principle that chromosomes drive not only spindle assembly but also other mitotic events essential for their own segregation. The direct function of chromosomes is not only to produce Ran-GTP but in addition to release important mitotic regulators from chromatin.

 [1] R.E. Carazo-Salas, et al., Nature, 400, 178 (1999), [2] O.J. Gruss, et al., Cell, 104, 83 (2001), [3] H. Yokoyama, et al., J Cell Biol, 180, 867 (2008), [4] H. Yokoyama, et al., Curr Biol, 23, 2443 (2013), [5] H. Yokoyama, et al., J Cell Biol, 187, 813 (2009)

日時：２０１４年３月１１日（火）　１４：００〜１５：００

場所：研究所1F セミナー室A

連絡先：広田　亨（内線5251）

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