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Vol. 16, Issue 3, 1056-1070, March 2005

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A Spindle Checkpoint Functions during Mitosis in the Early Caenorhabditis elegans Embryo

Sandra E. Encalada ^*, John Willis, Rebecca Lyczak , and Bruce Bowerman

Institute of Molecular Biology, University of Oregon, Eugene, OR 97403

Submitted August 17, 2004; Revised November 29, 2004; Accepted December 3, 2004
Monitoring Editor: Susan Strome

During mitosis, chromosome segregation is regulated by a spindle checkpoint mechanism. This checkpoint delays anaphase until all kinetochores are captured by microtubules from both spindle poles, chromosomes congress to the metaphase plate, and the tension between kinetochores and their attached microtubules is properly sensed. Although the spindle checkpoint can be activated in many different cell types, the role of this regulatory mechanism in rapidly dividing embryonic animal cells has remained controversial. Here, using time-lapse imaging of live embryonic cells, we show that chemical or mutational disruption of the mitotic spindle in early Caenorhabditis elegans embryos delays progression through mitosis. By reducing the function of conserved checkpoint genes in mutant embryos with defective mitotic spindles, we show that these delays require the spindle checkpoint. In the absence of a functional checkpoint, more severe defects in chromosome segregation are observed in mutants with abnormal mitotic spindles. We also show that the conserved kinesin CeMCAK, the CENP-F-related proteins HCP-1 and HCP-2, and the core kinetochore protein CeCENP-C all are required for this checkpoint. Our analysis indicates that spindle checkpoint mechanisms are functional in the rapidly dividing cells of an early animal embryo and that this checkpoint can prevent chromosome segregation defects during mitosis.

The online version of this article contains supplemental material at MBC Online (http://www.molbiolcell.org).

^* Present addresses: Department of Cellular and Molecular Medicine, University of California San Diego, Leichtag, LBR-411, La Jolla, CA 92093-0683;

Biology Department, Ursinus College, Collegeville, PA 19426.

Address correspondence to: Bruce Bowerman (bbowerman{at}molbio.uoregon.edu).

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