Abstract
Chromosomes are segregated by two antiparallel arrays of microtubules arranged to form the spindle apparatus. During cell division, the nucleation of cytosolic microtubules is prevented and spindle microtubules nucleate from centrosomes (in mitotic animal cells) or around chromosomes (in plants and some meiotic cells)1,2. The molecular mechanism by which chromosomes induce local microtubule nucleation in the absence of centrosomes is unknown3,4,5, but it can be studied by adding chromatin beads to Xenopus egg extracts6. The beads nucleate microtubules that eventually reorganize into a bipolar spindle. RCC1, the guanine-nucleotide-exchange factor for the GTPase protein Ran, is a component of chromatin. Using the chromatin bead assay, we show here that the activity of chromosome-associated RCC1 protein is required for spindle formation. Ran itself, when in the GTP-bound state (Ran-GTP), induces microtubule nucleation and spindle-like structures in M-phase extract. We propose thatRCC1 generates a high local concentration of Ran-GTP around chromatin which in turn induces the local nucleation of microtubules.
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Acknowledgements
We thank M. Dasso for antibodies and for discussing unpublished data; C. Klebe and A. Wittinghofer for pETRCC1; B. Soennichsen, M. Zerial, M. Fornerod, M. Ohno, G.-J. Arts and D.Bilbao-Cortes for Rab and Ran proteins; T. Surrey for participating in the ‘ethane trick’; and T.Wittmann and our colleagues for discussion and encouragement. G.G. was supported by a fellowship from the MURST Italian Ministry of Public Education and by an EMBO short-term fellowship, and O.J.G. was supported by an HFSPO award to I.W.M.
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Carazo-Salas, R., Guarguaglini, G., Gruss, O. et al. Generation of GTP-bound Ran by RCC1 is required for chromatin-induced mitotic spindle formation. Nature 400, 178–181 (1999). https://doi.org/10.1038/22133
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DOI: https://doi.org/10.1038/22133
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