|Ono, S. (2001) The Caenorhabditis
elegans unc-78 gene encodes a homologue of actin-interacting
protein 1 required for organized assembly of muscle actin filaments. J.Cell
Biol. 152, 1313-1319.
maintenance of myofibrils require dynamic regulation of the actin
cytoskeleton. In Caenorhabditis elegans, UNC-60B, a
muscle-specific actin depolymerizing factor (ADF)/cofilin isoform, is
required for proper actin filament assembly in body wall muscle (Ono,
S., D.L. Baillie, and G.M. Benian. 1999. J. Cell Biol.
145:491--502). Here, I show that UNC-78 is a homologue of
actin-interacting protein 1 (AIP1) and functions as a novel regulator of
actin organization in myofibrils. In unc-78 mutants, the striated
organization of actin filaments is disrupted, and large actin aggregates
are formed in the body wall muscle cells, resulting in defects in their
motility. Point mutations in unc-78 alleles change conserved residues
within different WD repeats of the UNC-78 protein and cause less severe
phenotypes than a deletion allele, suggesting that these mutations
partially impair the function of UNC-78. UNC-60B is normally localized
in the diffuse cytoplasm and to the myofibrils in wild type but
mislocalized to the actin aggregates in unc-78 mutants. Similar Unc-78
phenotypes are observed in both embryonic and adult muscles. Thus, AIP1
is an important regulator of actin filament organization and
localization of ADF/cofilin during development of myofibrils.