Flavin monooxygenases regulate Caenorhabditis elegans axon guidance and growth cone protrusion with UNC-6/Netrin signaling and Rac GTPases

Autor: Erik A. Lundquist, Mahekta R. Gujar, Aubrie M. Stricker
Rok vydání: 2017
Předmět:
0301 basic medicine
Cancer Research
Nematoda
Hydrolases
GTPase
Nervous System
Biochemistry
Mixed Function Oxygenases
Animals
Genetically Modified
Nerve Fibers
Animal Cells
Netrin
Medicine and Health Sciences
Pseudopodia
Receptor
Genetics (clinical)
Neurons
Motor Neurons
Nerves
Animal Models
Cell biology
Axon Guidance
rac GTP-Binding Proteins
Enzymes
Experimental Organism Systems
Netrins
Collapsin response mediator protein family
Signal transduction
Cellular Types
Anatomy
Signal Transduction
Research Article
lcsh:QH426-470
Dinitrocresols
Nerve Tissue Proteins
macromolecular substances
Biology
Research and Analysis Methods
03 medical and health sciences
Model Organisms
Semaphorin
Developmental Neuroscience
Genetics
Animals
Growth cone
Caenorhabditis elegans
Caenorhabditis elegans Proteins
Molecular Biology
Ecology
Evolution
Behavior and Systematics
Axon Guidance Receptors
fungi
Organisms
Biology and Life Sciences
Proteins
Cell Biology
Invertebrates
Axons
lcsh:Genetics
Guanosine Triphosphatase
030104 developmental biology
nervous system
Cellular Neuroscience
Mutation
Caenorhabditis
Enzymology
Axon guidance
Neuroscience
Zdroj: PLoS Genetics
PLoS Genetics, Vol 13, Iss 8, p e1006998 (2017)
ISSN: 1553-7404
Popis: The guidance cue UNC-6/Netrin regulates both attractive and repulsive axon guidance. Our previous work showed that in C. elegans, the attractive UNC-6/Netrin receptor UNC-40/DCC stimulates growth cone protrusion, and that the repulsive receptor, an UNC-5:UNC-40 heterodimer, inhibits growth cone protrusion. We have also shown that inhibition of growth cone protrusion downstream of the UNC-5:UNC-40 repulsive receptor involves Rac GTPases, the Rac GTP exchange factor UNC-73/Trio, and the cytoskeletal regulator UNC-33/CRMP, which mediates Semaphorin-induced growth cone collapse in other systems. The multidomain flavoprotein monooxygenase (FMO) MICAL (Molecule Interacting with CasL) also mediates growth cone collapse in response to Semaphorin by directly oxidizing F-actin, resulting in depolymerization. The C. elegans genome does not encode a multidomain MICAL-like molecule, but does encode five flavin monooxygenases (FMO-1, -2, -3, -4, and 5) and another molecule, EHBP-1, similar to the non-FMO portion of MICAL. Here we show that FMO-1, FMO-4, FMO-5, and EHBP-1 may play a role in UNC-6/Netrin directed repulsive guidance mediated through UNC-40 and UNC-5 receptors. Mutations in fmo-1, fmo-4, fmo-5, and ehbp-1 showed VD/DD axon guidance and branching defects, and variably enhanced unc-40 and unc-5 VD/DD axon guidance defects. Developing growth cones in vivo of fmo-1, fmo-4, fmo-5, and ehbp-1 mutants displayed excessive filopodial protrusion, and transgenic expression of FMO-5 inhibited growth cone protrusion. Mutations suppressed growth cone inhibition caused by activated UNC-40 and UNC-5 signaling, and activated Rac GTPase CED-10 and MIG-2, suggesting that these molecules are required downstream of UNC-6/Netrin receptors and Rac GTPases. From these studies we conclude that FMO-1, FMO-4, FMO-5, and EHBP-1 represent new players downstream of UNC-6/Netrin receptors and Rac GTPases that inhibit growth cone filopodial protrusion in repulsive axon guidance.
Author summary Mechanisms that guide axons to their targets in the developing nervous system have been elucidated, but how these pathways affect behavior of the growth cone of the axon during outgrowth remains poorly understood. We previously showed that the guidance cue UNC-6/Netrin and its receptors UNC-40/DCC and UNC-5 inhibit lamellipodial and filopodial growth cone protrusion to mediate repulsion from UNC-6/Netrin in C. elegans. Here we report a new mechanism downstream of UNC-6/Netrin involving flavin monooxygenase redox enzymes (FMOs). We show that FMOs are normally required for axon guidance and to inhibit growth cone protrusion. Furthermore, we show that they are required for the anti-protrusive effects of activated UNC-40 and UNC-5 receptors, and that they can partially compensate for loss of molecules in the pathway, indicating that they act downstream of UNC-6/Netrin signaling. Based on the function of the FMO-containing MICAL molecules in Drosophila and vertebrates, we speculate that the FMOs might directly oxidize actin, leading to filament disassembly and collapse, and/or lead to the phosphorylation of UNC-33/CRMP, which we show also genetically interacts with the FMOs downstream of UNC-6/Netrin. In conclusion, this is the first evidence that FMOs might act downstream of UNC-6/Netrin signaling in growth cone protrusion and axon repulsion.
Databáze: OpenAIRE
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