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Vol. 14, Issue 11, 4458-4469, November 2003
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* Institut für Genetik, Heinrich-Heine-Universität Düsseldorf, 40225 Düsseldorf, Germany;
Department of Biology, Indiana University, Bloomington, Indiana 47405-3700
Submitted May 7, 2003;
Revised July 11, 2003;
Accepted July 14, 2003
Monitoring Editor: Joseph Gall
The proper segregation of chromosomes during meiosis or mitosis requires the assembly of well organized spindles. In many organisms, meiotic spindles lack centrosomes. The formation of such acentrosomal spindles seems to involve first assembly or capture of microtubules (MTs) in a random pattern around the meiotic chromosomes and then parallel bundling and bipolar organization by the action of MT motors and other proteins. Here, we describe the structure, distribution, and function of KLP-18, a Caenorhabditis elegans Klp2 kinesin. Previous reports of Klp2 kinesins agree that it concentrates in spindles, but do not provide a clear view of its function. During prometaphase, metaphase, and anaphase, KLP-18 concentrates toward the poles in both meiotic and mitotic spindles. Depletion of KLP-18 by RNA-mediated interference prevents parallel bundling/bipolar organization of the MTs that accumulate around female meiotic chromosomes. Hence, meiotic chromosome segregation fails, leading to haploid or aneuploid embryos. Subsequent assembly and function of centrosomal mitotic spindles is normal except when aberrant maternal chromatin is present. This suggests that although KLP-18 is critical for organizing chromosome-derived MTs into a parallel bipolar spindle, the order inherent in centrosome-derived astral MT arrays greatly reduces or eliminates the need for KLP-18 organizing activity in mitotic spindles.
This article is dedicated to the memory of Christoph Segbert, an outstanding young scientist.
Online version of this article contains video material for some figures. Online version is available at www.molbiolcell.org
Corresponding author. E-mail address: bossinge{at}uni-duesseldorf.de
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