XMAP215 Is Required for the Microtubule-Nucleating Activity of Centrosomes

Microtubules are essential structures that organize the cytoplasm and form the mitotic spindle. Their number and orientation depend on the rate of nucleation events and their dynamics. Microtubules are often, but not always, nucleated off a single cytoplasmic element, the centrosome. One microtubule...

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Bibliographic Details
Published in:Current biology 2002-08, Vol.12 (15), p.1326-1330
Main Authors: Popov, Andrei V., Severin, Fedor, Karsenti, Eric
Format: Article
Language:English
Subjects:
Animals
Cell Nucleus - physiology
Cell Nucleus - ultrastructure
Centrosome - physiology
Centrosome - ultrastructure
Female
Microtubule-Associated Proteins - deficiency
Microtubule-Associated Proteins - genetics
Microtubule-Associated Proteins - metabolism
Microtubules - physiology
Microtubules - ultrastructure
Oocytes - physiology
Oocytes - ultrastructure
Tubulin - metabolism
Xenopus Proteins
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Summary:Microtubules are essential structures that organize the cytoplasm and form the mitotic spindle. Their number and orientation depend on the rate of nucleation events and their dynamics. Microtubules are often, but not always, nucleated off a single cytoplasmic element, the centrosome. One microtubule-associated protein, XMAP215 [1], is also a resident centrosomal protein [2]. In this study, we have found that XMAP215 is a key component for the microtubule-nucleating activity of centrosomes. We show that depletion of XMAP215 from Xenopus egg extracts impairs their ability to reconstitute the microtubule nucleation potential of salt-stripped centrosomes. We also show that XMAP215 immobilized on polymer beads induces the formation of microtubule asters in egg extracts as well as in solutions of pure tubulin. Formation of asters by XMAP215 beads indicates that this protein is able to anchor nascent microtubules via their minus ends. The aster-forming activity of XMAP215 does not require γ-tubulin in pure tubulin solutions, but it is γ-tubulin-dependent in egg extracts. Our results indicate that XMAP215, a resident centrosomal protein, contributes to the microtubule-nucleating activity of centrosomes, suggesting that, in vivo, the formation of asters by centrosomes requires factors additional to γ-tubulin.
ISSN:0960-9822
1879-0445
DOI:10.1016/S0960-9822(02)01033-3