Abstract
Asymmetric elevation of the Ca(2+) concentration in the growth cone can mediate both attractive and repulsive axon guidance. Ca(2+) signals that are accompanied by Ca(2+)-induced Ca(2+) release (CICR) trigger attraction, whereas Ca(2+) signals that are not accompanied by CICR trigger repulsion. The molecular machinery downstream of Ca(2+) signals, however, remains largely unknown. Here we report that asymmetric membrane trafficking mediates growth cone attraction. Local photolysis of caged Ca(2+), together with CICR, on one side of the growth cone of a chick dorsal root ganglion neuron facilitated the microtubule-dependent centrifugal transport of vesicles towards the leading edge and their subsequent vesicle-associated membrane-protein 2 (VAMP2)-mediated exocytosis on the side with an elevated Ca(2+) concentration. In contrast, Ca(2+) signals without CICR had no effect on the vesicle transport. Furthermore, pharmacological inhibition of VAMP2-mediated exocytosis prevented growth cone attraction, but not repulsion. These results strongly suggest that growth cone attraction and repulsion are driven by distinct mechanisms, rather than using the same molecular machinery with opposing polarities.
Publication types
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Research Support, Non-U.S. Gov't
MeSH terms
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Animals
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Antineoplastic Agents / pharmacology
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Axons / drug effects
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Axons / physiology*
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Biological Transport / drug effects
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Biological Transport / physiology
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Calcium / metabolism
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Calcium / pharmacology
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Cells, Cultured
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Chelating Agents / pharmacology
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Chick Embryo
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Cyclic AMP / analogs & derivatives
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Cyclic AMP / pharmacology
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Drug Interactions
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Egtazic Acid / analogs & derivatives
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Egtazic Acid / pharmacology
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Exocytosis / drug effects
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Exocytosis / physiology*
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Ganglia, Spinal / cytology
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Green Fluorescent Proteins / metabolism
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Growth Cones / drug effects
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Growth Cones / physiology*
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Metalloendopeptidases / pharmacology
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Neurons / cytology*
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Nocodazole / pharmacology
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Photolysis / drug effects
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Protein Kinase Inhibitors / pharmacology
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Pyridinium Compounds
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Quaternary Ammonium Compounds
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Tetanus Toxin / pharmacology
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Thionucleotides / pharmacology
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Transfection / methods
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Vesicle-Associated Membrane Protein 2 / metabolism
Substances
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Antineoplastic Agents
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Chelating Agents
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FM1 43
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Protein Kinase Inhibitors
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Pyridinium Compounds
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Quaternary Ammonium Compounds
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Tetanus Toxin
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Thionucleotides
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Vesicle-Associated Membrane Protein 2
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tetanospasmin
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1,2-bis(2-aminophenoxy)ethane N,N,N',N'-tetraacetic acid acetoxymethyl ester
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Green Fluorescent Proteins
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adenosine-3',5'-cyclic phosphorothioate
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Egtazic Acid
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Cyclic AMP
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Metalloendopeptidases
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Nocodazole
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Calcium