title: R-Ras controls axon branching through afadin in cortical neurons.
abstract: Regulation of axon growth, guidance, and branching is essential for constructing a correct neuronal network. R-Ras, a Ras-family small GTPase, has essential roles in axon formation and guidance. During axon formation, R-Ras activates a series of phosphatidylinositol 3-kinase signaling, inducing activation of a microtubule-assembly promoter-collapsin response mediator protein-2. However, signaling molecules linking R-Ras to actin cytoskeleton-regulating axonal morphology remain obscure. Here we identify afadin, an actin-binding protein harboring Ras association (RA) domains, as an effector of R-Ras inducing axon branching through F-actin reorganization. We observe endogenous interaction of afadin with R-Ras in cortical neurons during the stage of axonal development. Ectopic expression of afadin increases axon branch number, and the RA domains and the carboxyl-terminal F-actin binding domain are required for this action. RNA interference knockdown experiments reveal that knockdown of endogenous afadin suppressed both basal and R-Ras-mediated axon branching in cultured cortical neurons. Subcellular localization analysis shows that active R-Ras-induced translocation of afadin and its RA domains is responsible for afadin localizing to the membrane and inducing neurite development in Neuro2a cells. Overall, our findings demonstrate a novel signaling pathway downstream of R-Ras that controls axon branching.
authors.affiliation: Laboratory of Molecular Neurobiology, Graduate School of Biostudies, Kyoto University, Sakyo-ku, Kyoto, Japan.
authors.forename: Nariaki
authors.initials: N
authors.lastname: Iwasawa
authors.forename: Manabu
authors.initials: M
authors.lastname: Negishi
authors.forename: Izumi
authors.initials: I
authors.lastname: Oinuma
mesh_terms: D008841:Actin Cytoskeleton / Q000378:metabolism; D000818:Animals; D001369:Axons / Q000378:metabolism / Q000502:physiology* / Q000648:ultrastructure; D002454:Cell Differentiation; D002460:Cell Line; D049109:Cell Proliferation; D002540:Cerebral Cortex / Q000378:metabolism*; D057809:HEK293 Cells; D006801:Humans; D036341:Intercellular Signaling Peptides and Proteins / Q000235:genetics / Q000378:metabolism; D051379:Mice; D008840:Microfilament Proteins / Q000235:genetics / Q000378:metabolism*; D008870:Microtubules / Q000235:genetics / Q000378:metabolism; D009419:Nerve Tissue Proteins / Q000235:genetics / Q000378:metabolism; D055495:Neurogenesis; D058539:Phosphatidylinositol 3-Kinase / Q000378:metabolism; D011401:Promoter Regions, Genetic; D034622:RNA Interference; D034741:RNA, Small Interfering; D015398:Signal Transduction; D018631:ras Proteins / Q000378:metabolism*
chemical_list: D036341:Intercellular Signaling Peptides and Proteins; D008840:Microfilament Proteins; D009419:Nerve Tissue Proteins; D034741:RNA, Small Interfering; C108835:afadin; C095114:collapsin response mediator protein-2; D058539:Phosphatidylinositol 3-Kinase; C085929:RRAS protein, human; D018631:ras Proteins