title: Independent roles of Rho-GTPases in growth cone and axonal behavior.
abstract: Many external signals influence growth cone motility, pathfinding, and the formation of synapses that lead to the final map formation of the retinotectal system. Chick temporal retinal ganglion cell axons (RGCs) collapse and retract after encountering posterior tectal cells in vitro. During this process lateral extensions appear along the RGC axonal shaft. Lateral extensions appear as nascent interstitial axonal branches and also as defasciculating growth cones that are trailing along the pioneer axon. RGC branching controlled by repellent tectal cues has recently been shown to be the critical event in retinotectal map development. The intracellular mechanism underlying this phenomenon, however, is not understood. Inhibiting RhoA with either C3 toxin or inhibiting p160Rock kinase, an effector of RhoA, with Y27632 inhibited collapse, retraction, and the number of axons that showed lateral extensions. Lateral extension length increased significantly. Inhibiting Rac1A and cdc42 with cell permeable peptide inhibitors did not inhibit collapse of growth cones, but did inhibit axon retraction. In addition, the number of axons that showed lateral extensions and lateral extension length were significantly reduced. A dynamic cytoskeleton is necessary to react to incoming guidance information. This study addresses the problems of how growth cone motility and branching or defasciculation are affected by Rho-GTPases as extracellular signals are transmitted to the cytoskeleton.
authors.affiliation: Max-Planck Unit for Structural Molecular Biology, c/o Desy, Hamburg, Germany.
authors.forename: Edda
authors.initials: E
authors.lastname: Thies
authors.forename: Roger W
authors.initials: RW
authors.lastname: Davenport
mesh_terms: D036002:ADP Ribose Transferases / Q000494:pharmacology; D000577:Amides / Q000494:pharmacology; D000818:Animals; D001369:Axons / Q000187:drug effects / Q000502:physiology*; D001905:Botulinum Toxins / Q000494:pharmacology; D002478:Cells, Cultured; D002642:Chick Embryo; D046508:Culture Techniques; D004791:Enzyme Inhibitors / Q000494:pharmacology; D020439:Growth Cones / Q000187:drug effects / Q000502:physiology*; D007150:Immunohistochemistry; D018715:Microscopy, Video; D016501:Neurites / Q000502:physiology; D009474:Neurons / Q000502:physiology; D010446:Peptide Fragments / Q000494:pharmacology; D011554:Pseudopodia / Q000187:drug effects / Q000502:physiology; D011725:Pyridines / Q000494:pharmacology; D012165:Retinal Ganglion Cells / Q000187:drug effects / Q000502:physiology; D017385:Sequence Homology; D013477:Superior Colliculi / Q000502:physiology; D013997:Time Factors; D020764:cdc42 GTP-Binding Protein / Q000378:metabolism; D020830:rac1 GTP-Binding Protein / Q000378:metabolism; D020741:rho GTP-Binding Proteins / Q000378:metabolism / Q000502:physiology*
chemical_list: D000577:Amides; D004791:Enzyme Inhibitors; D010446:Peptide Fragments; D011725:Pyridines; C108830:Y 27632; D036002:ADP Ribose Transferases; C063007:exoenzyme C3, Clostridium botulinum; D001905:Botulinum Toxins; D020764:cdc42 GTP-Binding Protein; D020830:rac1 GTP-Binding Protein; D020741:rho GTP-Binding Proteins