A Formin Homology protein and a profilin are required for cytokinesis and Arp2/3-independent assembly of cortical microfilaments in C. elegans.
BACKGROUND
F-actin is enriched at the cortex of embryonic cells in the nematode Caenorhabditis elegans and is required for multiple processes that include the establishment of an anterior-posterior (A-P) axis and cytokinesis. However, the mechanisms that regulate cortical microfilament (MF) assembly remain poorly understood.


RESULTS
We show here that a profilin called PFN-1 accumulates at the cortex independent of the actin cytoskeleton and is required for the assembly or maintenance of cortical MFs and myosin. Reducing PFN-1 levels by RNAi results in cytokinesis and A-P polarity defects. PFN-1 binds to the Formin Homology (FH) protein CYK-1, which also is required for cortical MFs. In contrast to PFN-1 and CYK-1, the Arp2/3 complex appears to be dispensable for the assembly of cortical MFs, for A-P polarity, and for cytokinesis. Instead, the Arp2/3 complex is required for cell migrations that occur during gastrulation and may also be involved in cellular rearrangements required for epidermal enclosure prior to elongation of ovoid embryos into vermiform larvae.


CONCLUSIONS
We conclude that the FH protein CYK-1 and the profilin PFN-1 mediate the Arp2/3-independent assembly of MFs and are required for cytokinesis in the early embryo. These data suggest that CYK-1 and PFN-1 may nucleate MFs, as has recently been shown for an FH protein and a profilin in yeast.
Severson
Aaron F
AF
Institute of Molecular Biology, University of Oregon, Eugene, Oregon 97403-1229, USA.
Baillie
David L
DL
Bowerman
Bruce
B
D008841:Actin Cytoskeleton / Q000235:genetics / Q000378:metabolism*; D051377:Actin-Related Protein 2; D051378:Actin-Related Protein 3; D000199:Actins / Q000235:genetics / Q000378:metabolism*; D000205:Actomyosin / Q000235:genetics / Q000378:metabolism; D000818:Animals; D017173:Caenorhabditis elegans / Q000166:cytology* / Q000196:embryology / Q000502:physiology; D029742:Caenorhabditis elegans Proteins / Q000235:genetics / Q000378:metabolism*; D018797:Cell Cycle Proteins / Q000737:chemistry / Q000378:metabolism; D002455:Cell Division / Q000502:physiology; D002465:Cell Movement / Q000502:physiology; D016764:Cell Polarity / Q000502:physiology; D003285:Contractile Proteins; D004625:Embryo, Nonmammalian; D000080865:Formins; D005775:Gastrula / Q000378:metabolism; D046911:Macromolecular Substances; D008840:Microfilament Proteins / Q000235:genetics / Q000378:metabolism*; D051304:Profilins; D029702:Schizosaccharomyces pombe Proteins / Q000737:chemistry / Q000378:metabolism; D017386:Sequence Homology, Amino Acid
D051377:Actin-Related Protein 2; D051378:Actin-Related Protein 3; D000199:Actins; D029742:Caenorhabditis elegans Proteins; D018797:Cell Cycle Proteins; D003285:Contractile Proteins; C444419:FOR3 protein, S pombe; D000080865:Formins; D046911:Macromolecular Substances; D008840:Microfilament Proteins; D051304:Profilins; D029702:Schizosaccharomyces pombe Proteins; C476569:arx-1 protein, C elegans; C476568:arx-2 protein, C elegans; C114201:cyk-1 protein, C elegans; D000205:Actomyosin