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MBC in Press, published online ahead of print April 15, 2009
Mol. Biol. Cell 10.1091/mbc.E08-10-1051

A more recent version of this article appeared on June 1, 2009
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Submitted on October 22, 2008
Revised on March 13, 2009
Accepted on April 3, 2009

XMAP215-EB1 Interaction Is Required for Proper Spindle Assembly and Chromosome Segregation in Xenopus Egg Extract

Iva Kronja,* Anamarija Kruljac-Letunic,* Maïwen Caudron-Herger,{dagger} Peter Bieling,* and Eric Karsenti*

*Cell Biology and Biophysics Department, European Molecular Biology Laboratory, 69117 Heidelberg, Germany; {dagger}Deutsches Krebsforschungszentrum and Bioquant BQ24, 69120 Heidelberg, Germany

Monitoring Editor: David G. Drubin

In metaphase Xenopus egg extracts, global microtubule growth is mainly promoted by two unrelated microtubule-stabilizers, EB1 and XMAP215. Here, we explore their role and potential redundancy in the regulation of spindle assembly and function. We find that at physiological expression levels, both proteins are required for proper spindle architecture: Spindles assembled in the absence of EB1 or at decreased XMAP215 levels are short and frequently multipolar. Moreover, the reduced density of microtubules at the equator of {Delta}EB1 or {Delta}XMAP215 spindles leads to faulty kinetochore-microtubule attachments. These spindles also display diminished poleward flux rates and, upon anaphase induction, they neither segregate chromosomes nor reorganize into interphasic microtubule arrays. However, EB1 and XMAP215 nonredundantly regulate spindle assembly since an excess of XMAP215 can compensate for the absence of EB1, while the overexpression of EB1 cannot substitute for reduced XMAP215 levels. Our data indicate that EB1 could positively regulate XMAP215 by promoting its binding to the microtubules. Finally, we show that disruption of the mitosis-specific XMAP215-EB1 interaction, produces a phenotype similar to that of either EB1 or XMAP215 depletion. Therefore, the XMAP215-EB1 interaction is required for proper spindle organization and chromosome segregation in Xenopus egg extracts.

Address correspondence to: Eric Karsenti (karsenti{at}embl.de)




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