Abstract
Pathfinding axons change responses to guidance cues at intermediate targets. During midline crossing, spinal cord commissural axons acquire responsiveness to class 3 Semaphorins and Slits, which regulate their floor plate exit and restrict their post-crossing trajectory into a longitudinal pathway. We found that Sonic Hedgehog (Shh) could activate the repulsive response of pre-crossing axons to Semaphorins. Blocking Shh function with a monoclonal antibody to Shh, 5E1, in 'open-book' explants or by expressing a dominant-negative form of Patched-1, Ptch1(Delta loop2), or a Smoothened (Smo) shRNA construct in commissural neurons resulted in severe guidance defects, including stalling and knotting inside the floor plate, recrossing, randomized anterior-posterior projection and overshooting after crossing, reminiscent of Neuropilin-2 mutant embryos. Enhancing protein kinase A activity in pre-crossing axons diminished Shh-induced Semaphorin repulsion and caused profound midline stalling and overshooting/wandering of post-crossing axons. Therefore, a morphogen, Shh, can act as a switch of axon guidance responses.
Publication types
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Research Support, N.I.H., Extramural
MeSH terms
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Animals
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Antibodies, Monoclonal / pharmacology
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Axons / drug effects
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Axons / physiology*
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Body Patterning / drug effects
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Body Patterning / genetics
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Body Patterning / physiology*
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Cell Movement / physiology
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Cells, Cultured
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Chlorocebus aethiops
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Colforsin / pharmacology
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Cyclic AMP / metabolism
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Cyclic AMP-Dependent Protein Kinases / metabolism
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Embryo, Mammalian
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Functional Laterality / genetics
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Gene Expression Regulation, Developmental / drug effects
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Gene Expression Regulation, Developmental / physiology
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Green Fluorescent Proteins / genetics
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Hedgehog Proteins / genetics
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Hedgehog Proteins / immunology
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Hedgehog Proteins / physiology*
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Mice
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Mutation / genetics
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Neurons / cytology*
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Neurons / drug effects
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Neuropilin-2 / genetics
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Organ Culture Techniques
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Patched Receptors
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Patched-1 Receptor
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Rats
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Rats, Sprague-Dawley
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Rats, Transgenic
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Receptors, Cell Surface / genetics
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Semaphorins / genetics
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Semaphorins / metabolism*
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Signal Transduction / drug effects
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Signal Transduction / physiology
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Spinal Cord / cytology
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Spinal Cord / embryology
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Transfection / methods
Substances
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Antibodies, Monoclonal
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Hedgehog Proteins
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Neuropilin-2
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Patched Receptors
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Patched-1 Receptor
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Ptch1 protein, mouse
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Ptch1 protein, rat
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Receptors, Cell Surface
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Semaphorins
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Green Fluorescent Proteins
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Colforsin
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Cyclic AMP
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Cyclic AMP-Dependent Protein Kinases