title: Myosin and the PAR proteins polarize microfilament-dependent forces that shape and position mitotic spindles in Caenorhabditis elegans.
abstract: 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.
authors.affiliation: Institute of Molecular Biology, University of Oregon, Eugene, OR 97403-1229, USA.
authors.forename: Aaron F
authors.initials: AF
authors.lastname: Severson
authors.forename: Bruce
authors.initials: B
authors.lastname: Bowerman
mesh_terms: D008841:Actin Cytoskeleton / Q000187:drug effects / Q000378:metabolism* / Q000648:ultrastructure; D000818:Animals; D019086:Bridged Bicyclo Compounds, Heterocyclic / Q000494:pharmacology; D017173:Caenorhabditis elegans / Q000196:embryology / Q000378:metabolism* / Q000648:ultrastructure; D029742:Caenorhabditis elegans Proteins / Q000235:genetics / Q000378:metabolism; D002451:Cell Compartmentation / Q000187:drug effects / Q000235:genetics; D016764:Cell Polarity / Q000187:drug effects / Q000235:genetics*; D018385:Centrosome / Q000378:metabolism / Q000648:ultrastructure; D003285:Contractile Proteins; D000072159:Dynactin Complex; D004398:Dyneins / Q000235:genetics / Q000378:metabolism; D018507:Gene Expression Regulation, Developmental / Q000187:drug effects / Q000235:genetics; D008840:Microfilament Proteins / Q000172:deficiency / Q000235:genetics; D008869:Microtubule-Associated Proteins / Q000235:genetics / Q000378:metabolism; D008938:Mitosis / Q000187:drug effects / Q000502:physiology*; D009154:Mutation / Q000235:genetics; D024462:Myosin Type II / Q000172:deficiency / Q000235:genetics; D015739:Nocodazole / Q000494:pharmacology; D051304:Profilins; D017346:Protein Serine-Threonine Kinases; D008941:Spindle Apparatus / Q000187:drug effects / Q000378:metabolism* / Q000648:ultrastructure; D013844:Thiazoles / Q000494:pharmacology; D053778:Thiazolidines; D015053:Zygote / Q000187:drug effects / Q000378:metabolism* / Q000648:ultrastructure
chemical_list: D019086:Bridged Bicyclo Compounds, Heterocyclic; D029742:Caenorhabditis elegans Proteins; D003285:Contractile Proteins; D000072159:Dynactin Complex; D008840:Microfilament Proteins; D008869:Microtubule-Associated Proteins; D051304:Profilins; D013844:Thiazoles; D053778:Thiazolidines; C087977:par-2 protein, C elegans; C097238:PAR-3 protein, C elegans; D017346:Protein Serine-Threonine Kinases; D024462:Myosin Type II; D004398:Dyneins; D015739:Nocodazole; C037067:latrunculin A