title: The Rho guanine exchange factor RHGF-2 acts through the Rho-binding kinase LET-502 to mediate embryonic elongation in C. elegans.
abstract: Morphogenesis allows an organism to develop its final body shape. In Caenorhabditis elegans, a smooth muscle-like contraction of an actin/myosin network in the epidermis mediates the elongation of the worm embryo from a ball of cells into a long, thin worm. This process is controlled by two redundant pathways, one involving the small GTPase RHO-1 and its downstream effectors LET-502/Rho-binding kinase and MEL-11/myosin phosphatase, and another involving PAK-1/p21 activated kinase and FEM-2/PP2c phosphatase. Contraction occurs primarily in the lateral epidermal cells during elongation while the dorsal and ventral epidermal cells have a more passive role, and localized activity of a Rho GEF (guanine exchange factor) could contribute to this asymmetry. We found that loss of the C. elegans Rho GEF encoded by rhgf-2 results in arrest during early elongation. Genetically, rhgf-2 acts as an activator of let-502/Rho-binding kinase, in parallel to fem-2/PP2c phosphatase. Although expressed throughout the embryo, lateral cell-specific RHGF-2 expression can mediate elongation. The Rho GTPase activating protein (GAP) RGA-2 is known to inhibit contraction in the dorsal and ventral epidermis. Although rhgf-2 and rga-2 are individually lethal, the double mutant is viable with elongation still occurring in a let-502 dependent fashion. This indicates that LET-502/Rho-binding kinase has activity independent of the GEF and GAP. Finally, maternal LET-502 and MEL-11 are known to regulate the rate of cleavage furrow ingression in the early embryo and we show that maternal RHGF-2 also influences cleavage but RGA-2 does not. Thus while the LET-502/MEL-11 pathway is employed multiple times during embryogenesis, regulation by GEFs and GAPs differs at different points of the life cycle and fine tunes contractile function.
authors.affiliation: Department of Biochemistry and Molecular Biology, Alberta Children's Hospital Research Institute, University of Calgary, Calgary, Alberta T4N 1N4, Canada.
authors.forename: Benjamin G
authors.initials: BG
authors.lastname: Chan
authors.affiliation: Department of Biochemistry and Molecular Biology, Alberta Children's Hospital Research Institute, University of Calgary, Calgary, Alberta T4N 1N4, Canada.
authors.forename: Simon K
authors.initials: SK
authors.lastname: Rocheleau
authors.affiliation: Department of Biochemistry and Molecular Biology, Alberta Children's Hospital Research Institute, University of Calgary, Calgary, Alberta T4N 1N4, Canada.
authors.forename: Ryan B
authors.initials: RB
authors.lastname: Smit
authors.affiliation: Department of Biochemistry and Molecular Biology, Alberta Children's Hospital Research Institute, University of Calgary, Calgary, Alberta T4N 1N4, Canada. Electronic address: mains@ucalgary.ca.
authors.forename: Paul E
authors.initials: PE
authors.lastname: Mains
mesh_terms: D000483:Alleles; D000818:Animals; D049628:Body Size; D017173:Caenorhabditis elegans / Q000502:physiology*; D029742:Caenorhabditis elegans Proteins / Q000502:physiology*; D048749:Cytokinesis; D004817:Epidermis / Q000378:metabolism; D018507:Gene Expression Regulation, Developmental; D049452:Green Fluorescent Proteins / Q000378:metabolism; D020662:Guanine Nucleotide Exchange Factors / Q000502:physiology*; D008856:Microscopy, Fluorescence; D009024:Morphogenesis; D009154:Mutation; D016133:Polymerase Chain Reaction; D034622:RNA Interference; D013696:Temperature; D020741:rho GTP-Binding Proteins / Q000378:metabolism; D054460:rho-Associated Kinases / Q000502:physiology*
chemical_list: D029742:Caenorhabditis elegans Proteins; D020662:Guanine Nucleotide Exchange Factors; C573091:RHGF-2 protein, C elegans; D049452:Green Fluorescent Proteins; C515856:LET-502 protein, C elegans; D054460:rho-Associated Kinases; D020741:rho GTP-Binding Proteins
keywords: C. elegans; Embryo; Genetics; Guanine exchange factor; Morphogenesis; Rho