title: RPM-1, a Caenorhabditis elegans protein that functions in presynaptic differentiation, negatively regulates axon outgrowth by controlling SAX-3/robo and UNC-5/UNC5 activity.
abstract: Changes in axon outgrowth patterns are often associated with synaptogenesis. Members of the conserved Pam/Highwire/RPM-1 protein family have essential functions in presynaptic differentiation. Here, we show that Caenorhabditis elegans RPM-1 negatively regulates axon outgrowth mediated by the guidance receptors SAX-3/robo and UNC-5/UNC5. Loss-of-function rpm-1 mutations cause a failure to terminate axon outgrowth, resulting in an overextension of the longitudinal PLM axon. We observe that PLM overextension in rpm-1 mutants is suppressed by sax-3 and unc-5 loss-of-function mutations. PLM axon overextension is also induced by SAX-3 overexpression, and the length of extension is enhanced by loss of rpm-1 function or suppressed by loss of unc-5 function. We also observe that loss of rpm-1 function in genetic backgrounds sensitized for guidance defects disrupts ventral AVM axon guidance in a SAX-3-dependent manner and enhances dorsal guidance of DA and DB motor axons in an UNC-5-dependent manner. Loss of rpm-1 function alters expression of the green fluorescent protein (GFP)-tagged proteins, SAX-3::GFP and UNC-5::GFP. RPM-1 is known to regulate axon termination through two parallel genetic pathways; one involves the Rab GEF (guanine nucleotide exchange factor) GLO-4, which regulates vesicular trafficking, and another that involves the F-box protein FSN-1, which mediates RPM-1 ubiquitin ligase activity. We show that glo-4 but not fsn-1 mutations affect axon guidance in a manner similar to loss of rpm-1 function. Together, the results suggest that RPM-1 regulates axon outgrowth affecting axon guidance and termination by controlling the trafficking of the UNC-5 and SAX-3 receptors to cell membranes.
authors.affiliation: Department of Pathology and Laboratory Medicine, Robert Wood Johnson Medical School, University of Medicine and Dentistry of New Jersey, Piscataway, New Jersey 08854-5636, USA.
authors.forename: Haichang
authors.initials: H
authors.lastname: Li
authors.forename: Gauri
authors.initials: G
authors.lastname: Kulkarni
authors.forename: William G
authors.initials: WG
authors.lastname: Wadsworth
mesh_terms: D000818:Animals; D030801:Animals, Genetically Modified; D001369:Axons / Q000502:physiology*; D017173:Caenorhabditis elegans; D029742:Caenorhabditis elegans Proteins / Q000235:genetics / Q000378:metabolism* / Q000502:physiology*; D002454:Cell Differentiation / Q000235:genetics / Q000502:physiology*; D002465:Cell Movement / Q000235:genetics; D005786:Gene Expression Regulation / Q000235:genetics; D049452:Green Fluorescent Proteins / Q000378:metabolism; D020662:Guanine Nucleotide Exchange Factors / Q000235:genetics / Q000502:physiology*; D009154:Mutation / Q000235:genetics; D009419:Nerve Tissue Proteins / Q000235:genetics / Q000378:metabolism*; D009434:Neural Pathways / Q000502:physiology; D009474:Neurons / Q000166:cytology; D010812:Physical Stimulation / Q000379:methods; D017729:Presynaptic Terminals / Q000502:physiology*; D011956:Receptors, Cell Surface / Q000235:genetics / Q000378:metabolism*; D011971:Receptors, Immunologic / Q000235:genetics / Q000378:metabolism*; D013869:Thiolester Hydrolases / Q000502:physiology; D000097905:Roundabout Proteins; D000099301:Hydroxyacylglutathione Hydrolase
chemical_list: D029742:Caenorhabditis elegans Proteins; D049452:Green Fluorescent Proteins; D020662:Guanine Nucleotide Exchange Factors; D009419:Nerve Tissue Proteins; D011956:Receptors, Cell Surface; D011971:Receptors, Immunologic; D013869:Thiolester Hydrolases; D000097905:Roundabout Proteins; D000099301:Hydroxyacylglutathione Hydrolase; C409634:RPM-1 protein, C elegans; C077588:UNC-5 protein, C elegans