STAYING TRIM: HOW TRIM9 CONSTRAINS NEURONAL CELL MORPHOLOGY TO REGULATE CONNECTIVITY Public Deposited

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  • March 20, 2019
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  • Winkle, Cortney
    • Affiliation: School of Medicine, UNC Neuroscience Center, Neuroscience Curriculum
Abstract
  • The connectivity of the nervous system is established during development as axons branch and project to synaptic targets. The extracellular axon guidance cue Netrin-1 and its receptor Deleted in Colorectal Cancer (DCC) have established roles in axon branching and guidance. We found that TRIM9, an E3 ubiquitin ligase directly binds the cytoplasmic tail of DCC. In the absence of TRIM9, murine embryonic cortical neurons exhibit excessive SNARE mediated exocytic activity and defective axon branching both in vitro and in vivo. These neurons also exhibit defects in DCC expression, localization, and downstream signaling through Focal Adhesion Kinase (FAK). We identified a Netrin-1-sensitive interaction between TRIM9 and the SNARE component SNAP25 which constrains SNARE-mediated exocytosis and axon branching. We found that DCC is ubiquitinated in the presence of TRIM9 and the absence of Netrin-1, which modulates steady state cellular levels of DCC. Genetic loss of Trim9 impaired both clustering and multimerization of the DCC receptor in response to Netrin-1, independent of ubiquitination. Downstream of DCC, both Netrin-1 stimulation and loss of Trim9 facilitate tyrosine phosphorylation and activation of Focal Adhesion Kinase(FAK). Pharmacological inhibition of FAK activation inhibited Netrin-1 dependent and aberrant exocytosis and axon branching, but did not impact SNARE complex formation suggesting a novel role for FAK in SNARE conformation switching from cis to trans. In the hippocampus, genetic loss of Trim9 significantly altered the morphology of both developing and adult born neurons, impaired localization of adult born neurons, and contributed to abnormal circuitry and defective spatial learning and memory. Taken together, these results indicate that TRIM9 is a novel coordinator of membrane trafficking and plasma membrane expansion during neuronal development. Further, these data suggest that the precise temporal and spatial control of axonal and dendritic arborization is critical for proper formation and function of neural circuitry in the developing and adult nervous system.
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  • In Copyright
Advisor
  • Cheney, Richard
  • Weinberg, Richard J.
  • Deshmukh, Mohanish
  • Anton, Eva
  • Gupton, Stephanie
Degree
  • Doctor of Philosophy
Degree granting institution
  • University of North Carolina at Chapel Hill Graduate School
Graduation year
  • 2016
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