title: Rho inhibition recruits DCC to the neuronal plasma membrane and enhances axon chemoattraction to netrin 1.
abstract: Molecular cues, such as netrin 1, guide axons by influencing growth cone motility. Rho GTPases are a family of intracellular proteins that regulate the cytoskeleton, substrate adhesion and vesicle trafficking. Activation of the RhoA subfamily of Rho GTPases is essential for chemorepellent axon guidance; however, their role during axonal chemoattraction is unclear. Here, we show that netrin 1, through its receptor DCC, inhibits RhoA in embryonic spinal commissural neurons. To determine whether netrin 1-mediated chemoattraction requires Rho function, we inhibited Rho signaling and assayed axon outgrowth and turning towards netrin 1. Additionally, we examined two important mechanisms that influence the guidance of axons to netrin 1: substrate adhesion and transport of the netrin receptor DCC to the plasma membrane. We found that inhibiting Rho signaling increased plasma membrane DCC and adhesion to substrate-bound netrin 1, and also enhanced netrin 1-mediated axon outgrowth and chemoattractive axon turning. Conversely, overexpression of RhoA or constitutively active RhoA inhibited axonal responses to netrin 1. These findings provide evidence that Rho signaling reduces axonal chemoattraction to netrin 1 by limiting the amount of plasma membrane DCC at the growth cone, and suggest that netrin 1-mediated inhibition of RhoA activates a positive-feedback mechanism that facilitates chemoattraction to netrin 1. Notably, these findings also have relevance for CNS regeneration research. Inhibiting RhoA promotes axon regeneration by disrupting inhibitory responses to myelin and the glial scar. By contrast, we demonstrate that axon chemoattraction to netrin 1 is not only maintained but enhanced, suggesting that this might facilitate directing regenerating axons to appropriate targets.
authors.affiliation: Centre for Neuronal Survival, Montreal Neurological Institute, Program in NeuroEngineering, Department of Neurology and Neurosurgery, McGill University, Montreal, Quebec H3A 2B4, Canada.
authors.forename: Simon W
authors.initials: SW
authors.lastname: Moore
authors.forename: James P
authors.initials: JP
authors.lastname: Correia
authors.forename: Karen
authors.initials: K
authors.lastname: Lai Wing Sun
authors.forename: Madeline
authors.initials: M
authors.lastname: Pool
authors.forename: Alyson E
authors.initials: AE
authors.lastname: Fournier
authors.forename: Timothy E
authors.initials: TE
authors.lastname: Kennedy
mesh_terms: D000818:Animals; D001369:Axons / Q000187:drug effects / Q000201:enzymology / Q000378:metabolism*; D002448:Cell Adhesion / Q000187:drug effects; D002462:Cell Membrane / Q000187:drug effects / Q000378:metabolism*; D002633:Chemotaxis / Q000187:drug effects*; D000075389:DCC Receptor; D004622:Embryo, Mammalian / Q000166:cytology / Q000201:enzymology; D004789:Enzyme Activation / Q000187:drug effects; D005260:Female; D020439:Growth Cones / Q000187:drug effects / Q000201:enzymology; D006801:Humans; D009414:Nerve Growth Factors / Q000494:pharmacology*; D000075388:Netrin-1; D011493:Protein Kinase C / Q000378:metabolism; D021381:Protein Transport / Q000187:drug effects; D051381:Rats; D017207:Rats, Sprague-Dawley; D011956:Receptors, Cell Surface / Q000378:metabolism*; D015398:Signal Transduction / Q000187:drug effects; D025521:Tumor Suppressor Proteins / Q000378:metabolism* / Q000494:pharmacology*; D054460:rho-Associated Kinases / Q000378:metabolism; D020742:rhoA GTP-Binding Protein / Q000037:antagonists & inhibitors*
chemical_list: D000075389:DCC Receptor; C501912:Dcc protein, rat; C000617351:NTN1 protein, human; D009414:Nerve Growth Factors; C000617354:Ntn1 protein, rat; D011956:Receptors, Cell Surface; D025521:Tumor Suppressor Proteins; D000075388:Netrin-1; C061570:protein kinase N; D054460:rho-Associated Kinases; D011493:Protein Kinase C; D020742:rhoA GTP-Binding Protein