Trio’s Rho-specific GEF domain is the missing Gαq effector in C. elegans

  1. Stacey L. Williams1,
  2. Susanne Lutz2,
  3. Nicole K. Charlie1,
  4. Christiane Vettel2,
  5. Michael Ailion3,
  6. Cassandra Coco4,
  7. John J.G. Tesmer4,
  8. Erik M. Jorgensen3,
  9. Thomas Wieland2, and
  10. Kenneth G. Miller1,5
  1. 1 Program in Molecular, Cell, and Developmental Biology, Oklahoma Medical Research Foundation, Oklahoma City, Oklahoma 73104, USA;
  2. 2 Institute of Experimental and Clinical Pharmacology, Medical Faculty Mannheim, University of Heidelberg, D-68169 Mannheim, Germany;
  3. 3 Department of Biology, Howard Hughes Medical Institute, University of Utah, Salt Lake City, Utah 84112, USA;
  4. 4 Department of Pharmacology, Life Sciences Institute, University of Michigan, Ann Arbor, Michigan 48109, USA

Abstract

The Gαq pathway is essential for animal life and is a central pathway for driving locomotion, egg laying, and growth in Caenorhabditis elegans, where it exerts its effects through EGL-8 (phospholipase Cβ [PLCβ]) and at least one other effector. To find the missing effector, we performed forward genetic screens to suppress the slow growth and hyperactive behaviors of mutants with an overactive Gαq pathway. Four suppressor mutations disrupted the Rho-specific guanine-nucleotide exchange factor (GEF) domain of UNC-73 (Trio). The mutations produce defects in neuronal function, but not neuronal development, that cause sluggish locomotion similar to animals lacking EGL-8 (PLCβ). Strains containing null mutations in both EGL-8 (PLCβ) and UNC-73 (Trio RhoGEF) have strong synthetic phenotypes that phenocopy the arrested growth and near-complete paralysis of Gαq-null mutants. Using cell-based and biochemical assays, we show that activated C. elegansq synergizes with Trio RhoGEF to activate RhoA. Activated Gαq and Trio RhoGEF appear to be part of a signaling complex, because they coimmunoprecipitate when expressed together in cells. Our results show that Trio’s Rho-specific GEF domain is a major Gαq effector that, together with PLCβ, mediates the Gαq signaling that drives the locomotion, egg laying, and growth of the animal.

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