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MBC in Press, published online ahead of print December 22, 2004
Mol. Biol. Cell 10.1091/mbc.E04-08-0712

A more recent version of this article appeared on March 1, 2005
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Submitted on August 17, 2004
Revised on November 29, 2004
Accepted on December 3, 2004

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

Sandra E. Encalada,* John Willis, Rebecca Lyczak,{dagger} and Bruce Bowerman{ddagger}

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

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. While 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 C. 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. 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. In the absence of a functional checkpoint, more severe defects in chromosome segregation are observed in mutants with abnormal mitotic spindles. 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.

Present addresses: *Department of Cellular and Molecular Medicine, UCSD, Leichtag, LBR-411, La Jolla, CA 92093-0683; {dagger}Biology Department, Ursinus College, Collegeville, PA 19426.

{ddagger}Corresponding author. E-mail: bbowerman{at}molbio.uoregon.edu






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