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CaM kinase II initiates meiotic spindle depolymerization independently of APC/C activation

¹ Zentrum für Molekulare Biologie der Universität Heidelberg, Deutsches Krebsforschungszentrum und Zentrum für Molekulare Biologie Heidelberg Allianz (DKFZ-ZMBH Alliance), 69120 Heidelberg, Germany
² Cell Biology and Biophysics Program, European Molecular Biology Laboratory, 69126 Heidelberg, Germany

Correspondence to Oliver J. Gruss: o.gruss{at}zmbh.uni-heidelberg.de

Altered spindle microtubule dynamics at anaphase onset are the basis for chromosome segregation. In Xenopus laevis egg extracts, increasing free calcium levels and subsequently rising calcium-calmodulin–dependent kinase II (CaMKII) activity promote a release from meiosis II arrest and reentry into anaphase. CaMKII induces the activation of the anaphase-promoting complex/cyclosome (APC/C), which destines securin and cyclin B for degradation to allow chromosome separation and mitotic exit.

In this study, we investigated the calcium-dependent signal responsible for microtubule depolymerization at anaphase onset after release from meiotic arrest in Xenopus egg extracts. Using Ran–guanosine triphosphate–mediated microtubule assemblies and quantitative analysis of complete spindles, we demonstrate that CaMKII triggers anaphase microtubule depolymerization. A CaMKII-induced twofold increase in microtubule catastrophe rates can explain reduced microtubule stability. However, calcium or constitutively active CaMKII promotes microtubule destabilization even upon APC/C inhibition and in the presence of high cyclin-dependent kinase 1 activity. Therefore, our data demonstrate that CaMKII turns on parallel pathways to activate the APC/C and to induce microtubule depolymerization at meiotic anaphase onset.

Abbreviations used in this paper: APC/C, anaphase-promoting complex/cyclosome; CaMKII, calcium-calmodulin–dependent kinase II; CSF, cytostatic factor; MAP, microtubule-associated protein; XErp, Xenopus Emi1-related protein.

© 2008 Reber et al. This article is distributed under the terms of an Attribution–Noncommercial–Share Alike–No Mirror Sites license for the first six months after the publication date (see http://www.jcb.org/misc/terms.shtml). After six months it is available under a Creative Commons License (Attribution–Noncommercial–Share Alike 3.0 Unported license, as described at http://creativecommons.org/licenses/by-nc-sa/3.0/).

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