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MBC in Press, published online ahead of print August 29, 2007
Mol. Biol. Cell 10.1091/mbc.E07-02-0105

A more recent version of this article appeared on November 1, 2007
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Submitted on February 6, 2007
Revised on August 8, 2007
Accepted on August 16, 2007

PAR-3 and PAR-1 Inhibit LET-99 Localization to Generate a Cortical Band Important for Spindle Positioning in Caenorhabditis elegans Embryos

Jui-Ching Wu and Lesilee S. Rose

Section of Molecular and Cellular Biology, University of California, Davis, CA 95616

Monitoring Editor: Fred Chang

The conserved PAR proteins are localized in asymmetric cortical domains and are required for the polarized localization of cell fate determinants in many organisms. In C. elegans embryos, LET-99 and G protein signaling act downstream of the PARs to regulate spindle positioning and ensure asymmetric division. PAR-3 and PAR-2 localize LET-99 to a posterior cortical band through an unknown mechanism. Here we report that LET-99 asymmetry depends on cortically localized PAR-1 and PAR-4 but not on cytoplasmic polarity effectors. In par-1 and par-4 embryos, LET-99 accumulates at the entire posterior cortex, but remains at low levels at the anterior cortex occupied by PAR-3. Further, PAR-3 and PAR-1 have graded cortical distributions with the highest levels at the anterior and posterior poles respectively, and the lowest levels of these proteins correlates with high LET-99 accumulation. These results suggest that PAR-3 and PAR-1 inhibit the localization of LET-99 to generate a band pattern. In addition, PAR-1 kinase activity is required for the inhibition of LET-99 localization and PAR-1 associates with LET-99. Finally, examination of par-1 embryos suggests that the banded pattern of LET-99 is critical for normal posterior spindle displacement and to prevent spindle misorientation caused by cell shape constraints.

Address correspondence to: Lesilee S. Rose (lsrose{at}ucdavis.edu)






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