title: The E3 Ubiquitin Ligase TRIM9 Is a Filopodia Off Switch Required for Netrin-Dependent Axon Guidance.
abstract: Neuronal growth cone filopodia contain guidance receptors and contribute to axon guidance; however, the mechanism by which the guidance cue netrin increases filopodia density is unknown. Here, we demonstrate that TRIM9, an E3 ubiquitin ligase that localizes to filopodia tips and binds the netrin receptor DCC, interacts with and ubiquitinates the barbed-end polymerase VASP to modulate filopodial stability during netrin-dependent axon guidance. Studies with murine Trim9(+/+) and Trim9(-/-) cortical neurons, along with a non-ubiquitinatable VASP mutant, demonstrate that TRIM9-mediated ubiquitination of VASP reduces VASP filopodial tip localization, VASP dynamics at tips, and filopodial stability. Upon netrin treatment, VASP is deubiquitinated, which promotes VASP tip localization and filopodial stability. Trim9 deletion induces axon guidance defects in vitro and in vivo, whereas a gradient of deubiquitinase inhibition promotes axon turning in vitro. We conclude that a gradient of TRIM9-mediated ubiquitination of VASP creates a filopodial stability gradient during axon turning.
authors.affiliation: UNC Department of Cell Biology and Physiology, 111 Mason Farm Road, Chapel Hill, NC 27599, USA.
authors.forename: Shalini
authors.initials: S
authors.lastname: Menon
authors.affiliation: UNC Neurobiology Curriculum, 115 Mason Farm Road, Chapel Hill, NC 27599, U.S.A.
authors.forename: Nicholas Patrick
authors.initials: NP
authors.lastname: Boyer
authors.affiliation: UNC Neurobiology Curriculum, 115 Mason Farm Road, Chapel Hill, NC 27599, U.S.A.
authors.forename: Cortney Chelise
authors.initials: CC
authors.lastname: Winkle
authors.affiliation: MIT Koch Institute, 500 Main Street, Cambridge, MA 02139, USA.
authors.forename: Leslie Marie
authors.initials: LM
authors.lastname: McClain
authors.affiliation: MIT Koch Institute, 500 Main Street, Cambridge, MA 02139, USA.
authors.forename: Christopher Carey
authors.initials: CC
authors.lastname: Hanlin
authors.affiliation: Division of Clinical Pharmacology, Department of Medicine IV, KUM, Ludwig-Maximilian University, Ziemssenstrasse 1, D-80336 Munich, Germany.
authors.forename: Dharmendra
authors.initials: D
authors.lastname: Pandey
authors.affiliation: Division of Clinical Pharmacology, Department of Medicine IV, KUM, Ludwig-Maximilian University, Ziemssenstrasse 1, D-80336 Munich, Germany.
authors.forename: Simon
authors.initials: S
authors.lastname: Rothenfußer
authors.affiliation: UNC/NCSU Joint Department of Biomedical Engineering, 333 South Columbia Street, Chapel Hill, NC 27517, USA.|UNC Neuroscience Center, 115 Mason Farm Road, Chapel Hill, NC 27599, USA.|Carolina Institute for Developmental Disabilities, 101 Renee Lynne Ct, Carrboro, NC 27510, USA.
authors.forename: Anne Marion
authors.initials: AM
authors.lastname: Taylor
authors.affiliation: UNC Department of Cell Biology and Physiology, 111 Mason Farm Road, Chapel Hill, NC 27599, USA.|UNC Neuroscience Center, 115 Mason Farm Road, Chapel Hill, NC 27599, USA.|UNC Lineberger Comprehensive Cancer Center, 101 Manning Dr, Chapel Hill, NC 27514, USA.
authors.forename: Stephanie Lynn
authors.initials: SL
authors.lastname: Gupton
mesh_terms: D000818:Animals; D001369:Axons / Q000378:metabolism*; D002352:Carrier Proteins / Q000235:genetics / Q000378:metabolism*; D020439:Growth Cones / Q000378:metabolism*; D008810:Mice, Inbred C57BL; D008822:Mice, Transgenic; D009414:Nerve Growth Factors / Q000378:metabolism; D009419:Nerve Tissue Proteins / Q000235:genetics / Q000378:metabolism*; D055495:Neurogenesis / Q000502:physiology*; D009474:Neurons / Q000378:metabolism*; D015398:Signal Transduction / Q000502:physiology; D044767:Ubiquitin-Protein Ligases / Q000378:metabolism*
chemical_list: D002352:Carrier Proteins; D009414:Nerve Growth Factors; D009419:Nerve Tissue Proteins; C469337:Trim9 protein, mouse; D044767:Ubiquitin-Protein Ligases