QUICK SEARCH:   [advanced] Author: Keyword(s): Year:  Vol:  Page:

Vol. 17, Issue 3, 1051-1064, March 2006

This Article Full Text Full Text (PDF) Supplemental Material All Versions of this Article: E05-09-0886v1 17/3/1051    most recent Alert me when this article is cited Alert me if a correction is posted Services Similar articles in this journal Similar articles in PubMed Alert me to new issues of the journal Download to citation manager Citing Articles Citing Articles via Google Scholar Google Scholar Articles by Willis, J. H. Articles by Bowerman, B. Search for Related Content PubMed PubMed Citation Articles by Willis, J. H. Articles by Bowerman, B.

Conditional Dominant Mutations in the Caenorhabditis elegans Gene act-2 Identify Cytoplasmic and Muscle Roles for a Redundant Actin Isoform

John H. Willis ^*, Edwin Munro , Rebecca Lyczak ^* , and Bruce Bowerman ^*

^* Institute of Molecular Biology, University of Oregon, Eugene, OR 97403; Center for Cell Dynamics and Friday Harbor Laboratories, University of Washington, Friday Harbor, WA 98250

Submitted September 23, 2005; Revised December 30, 2005; Accepted January 4, 2006
Monitoring Editor: Sandra Schmid

Animal genomes each encode multiple highly conserved actin isoforms that polymerize to form the microfilament cytoskeleton. Previous studies of vertebrates and invertebrates have shown that many actin isoforms are restricted to either nonmuscle (cytoplasmic) functions, or to myofibril force generation in muscle cells. We have identified two temperature-sensitive and semidominant embryonic-lethal Caenorhabditis elegans mutants, each with a single mis-sense mutation in act-2, one of five C. elegans genes that encode actin isoforms. These mutations alter conserved and adjacent amino acids predicted to form part of the ATP binding pocket of actin. At the restrictive temperature, both mutations resulted in aberrant distributions of cortical microfilaments associated with abnormal and striking membrane ingressions and protrusions. In contrast to the defects caused by these dominant mis-sense mutations, an act-2 deletion did not result in early embryonic cell division defects, suggesting that additional and redundant actin isoforms are involved. Accordingly, we found that two additional actin isoforms, act-1 and act-3, were required redundantly with act-2 for cytoplasmic function in early embryonic cells. The act-1 and -3 genes also have been implicated previously in muscle function. We found that an ACT-2::GFP reporter was expressed cytoplasmically in embryonic cells and also was incorporated into contractile filaments in adult muscle cells. Furthermore, one of the dominant act-2 mutations resulted in uncoordinated adult movement. We conclude that redundant C. elegans actin isoforms function in both muscle and nonmuscle contractile processes.

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

Present address: Biology Department, Ursinus College, Collegeville, PA 19426.

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