RhoA activation during polarization and cytokinesis of the early Caenorhabditis elegans embryo is differentially dependent on NOP-1 and CYK-4

Mol Biol Cell. 2012 Oct;23(20):4020-31. doi: 10.1091/mbc.E12-04-0268. Epub 2012 Aug 23.


The GTPase RhoA is a central regulator of cellular contractility in a wide variety of biological processes. During these events, RhoA is activated by guanine nucleotide exchange factors (GEFs). These molecules are highly regulated to ensure that RhoA activation occurs at the proper time and place. During cytokinesis, RhoA is activated by the RhoGEF ECT-2. In human cells, ECT-2 activity requires its association with CYK-4, which is a component of the centralspindlin complex. In contrast, in early Caenorhabditis elegans embryos, not all ECT-2-dependent functions require CYK-4. In this study, we identify a novel protein, NOP-1, that functions in parallel with CYK-4 to promote RhoA activation. We use mutations in nop-1 and cyk-4 to dissect cytokinesis and cell polarization. NOP-1 makes a significant, albeit largely redundant, contribution to cytokinesis. In contrast, NOP-1 is required for the preponderance of RhoA activation during the establishment phase of polarization.

Publication types

  • Research Support, N.I.H., Extramural
  • Research Support, Non-U.S. Gov't

MeSH terms

  • Animals
  • Caenorhabditis elegans / cytology*
  • Caenorhabditis elegans / embryology
  • Caenorhabditis elegans / enzymology
  • Caenorhabditis elegans Proteins / metabolism*
  • Carrier Proteins / metabolism*
  • Cell Polarity*
  • Cytokinesis*
  • Embryo, Nonmammalian / cytology*
  • Enzyme Activation
  • Green Fluorescent Proteins / metabolism
  • Guanine Nucleotide Exchange Factors / metabolism
  • Humans
  • Models, Biological
  • Protein Transport
  • Recombinant Fusion Proteins / metabolism
  • rhoA GTP-Binding Protein / metabolism*


  • CYK-4 protein, C elegans
  • Caenorhabditis elegans Proteins
  • Carrier Proteins
  • Ect-2 protein, C elegans
  • Guanine Nucleotide Exchange Factors
  • Recombinant Fusion Proteins
  • Green Fluorescent Proteins
  • rhoA GTP-Binding Protein