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Published 14 April 2003. doi:10.1083/jcb.200210171
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© The Rockefeller University Press, 0021-9525/2003/4/21 $5.00
The Journal of Cell Biology, Volume 161, Number 1, 21-26

Report

 Myosin and the PAR proteins polarize microfilament-dependent forces that shape and position mitotic spindles in Caenorhabditis elegans

Aaron F. Severson and Bruce Bowerman

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

Address correspondence to Bruce Bowerman, Institute of Molecular Biology, 1370 Franklin Blvd., University of Oregon, Eugene, OR 97403-1229. Tel.: (541) 346-0853. Fax: (541) 346-5891. E-mail: bbowerman{at}molbio.uoregon.edu

In Caenorhabditis elegans, the partitioning proteins (PARs), microfilaments (MFs), dynein, dynactin, and a nonmuscle myosin II all localize to the cortex of early embryonic cells. Both the PARs and the actomyosin cytoskeleton are required to polarize the anterior-posterior (a-p) body axis in one-cell zygotes, but it remains unknown how MFs influence embryonic polarity. Here we show that MFs are required for the cortical localization of PAR-2 and PAR-3. Furthermore, we show that PAR polarity regulates MF-dependent cortical forces applied to astral microtubules (MTs). These forces, which appear to be mediated by dynein and dynactin, produce changes in the shape and orientation of mitotic spindles. Unlike MFs, dynein, and dynactin, myosin II is not required for the production of these forces. Instead, myosin influences embryonic polarity by limiting PAR-3 to the anterior cortex. This in turn produces asymmetry in the forces applied to MTs at each pole and allows PAR-2 to accumulate in the posterior cortex of a one-cell zygote and maintain asymmetry.

Key Words: dynein ATPase; microfilaments; myosin type II; mitotic spindle apparatus; cell polarity

* Abbreviations used in this paper: a-p, anterior-posterior; DHC, dynein heavy chain; DNC, dynactin component p150glued; LatA: latrunculin A; MF, microfilament; MLC, myosin II regulatory light chain; MT, microtubule; NCC, nucleocentrosomal complex; NMY, nonmuscle myosin II heavy chain; PAR, partitioning protein; RNAi, double stranded RNA-mediated interference.


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