title: Control of embryonic spindle positioning and Galpha activity by C. elegans RIC-8.
abstract: Asymmetric spindle positioning is of fundamental importance for generating cell diversity during development. In the C. elegans 1 cell embryo, spindle positioning has been shown to depend on heterotrimeric G protein signaling. Two Galpha subunits, GOA-1 and GPA-16 (hereafter Galpha), and receptor independent activators of G protein signaling GPR-1 and GPR-2 (GPR-1/2) are required for proper regulation of spindle positioning . However, it remains unclear whether Galpha regulates spindle positioning in its GDP or GTP bound form. Here, we investigate the role of RIC-8 in this pathway. RIC-8 was genetically shown to act in concert with goa-1 to regulate centrosome movements in C. elegans . Interestingly, mammalian RIC-8 was recently found to behave as a GEF for Galpha subunits in vitro . We show that reduction of function of ric-8 results in a 1 cell embryo phenotype very similar to the phenotype of embryos depleted of Galpha. RIC-8 is able to directly bind to GOA-1, preferentially to GOA-1-GDP, consistent with a GEF role. RIC-8 is localized at the embryo cortex, and its activity is essential for the asymmetric localization of GPR-1/2. We suggest that RIC-8 directly modulates Galpha activity and that Galpha-GTP is the signaling molecule regulating spindle positioning in the early embryo.
authors.affiliation: Institute of Biochemistry, ETH (Eidgenössische Technische Hochschule) Hoenggerberg, 8093 Zürich, Switzerland.
authors.forename: Claudia
authors.initials: C
authors.lastname: Couwenbergs
authors.forename: Annina C
authors.initials: AC
authors.lastname: Spilker
authors.forename: Monica
authors.initials: M
authors.lastname: Gotta
mesh_terms: D000818:Animals; D017173:Caenorhabditis elegans / Q000235:genetics / Q000378:metabolism*; D029742:Caenorhabditis elegans Proteins / Q000235:genetics / Q000378:metabolism*; D004625:Embryo, Nonmammalian / Q000378:metabolism; D044385:GTP-Binding Protein alpha Subunits / Q000378:metabolism*; D020662:Guanine Nucleotide Exchange Factors; D007150:Immunohistochemistry; D018715:Microscopy, Video; D009687:Nuclear Proteins / Q000235:genetics / Q000378:metabolism*; D015398:Signal Transduction; D008941:Spindle Apparatus / Q000378:metabolism*; D020798:Two-Hybrid System Techniques
chemical_list: D029742:Caenorhabditis elegans Proteins; C475458:G protein regulator 1, C elegans; C475459:G protein regulator 2, C elegans; D044385:GTP-Binding Protein alpha Subunits; D020662:Guanine Nucleotide Exchange Factors; D009687:Nuclear Proteins; C413418:RIC-8 protein, C elegans; C480838:GPA-16 protein, C elegans