Gupton, S. | bioRxiv Science

bioRxiv2019

A pair of E3 ubiquitin ligases compete to regulate axon guidance and filopodial dynamics

Appropriate axon guidance is necessary to form accurate neuronal connections. Guidance cues stimulate reorganization of the cytoskeleton within the distal growth cone at the tip of the extending axon. Filopodia at the periphery of the growth cone have long been considered sensors for axon guidance cues, yet how they perceive and respond to extracellular cues remains ill-defined. Our previous work found that the filopodial actin polymerase VASP is regulated via TRIM9-dependent nondegradative ubiquitination, and that appropriate VASP ubiquitination and deubiquitination are required for axon turning in response to the guidance cue netrin-1. Here we show that the TRIM9-related protein TRIM67 antagonizes VASP ubiquitination by outcompeting the TRIM9:VASP interaction. This antagonistic role is required for netrin-1 dependent filopodial responses, axon turning and branching, and fiber tract formation. We suggest a novel model that coordinated regulation of nondegradative VASP ubiquitination by a pair of ligases is a critical element of axon guidance.

cell biology↗

bioRxiv2017

The Class I E3 Ubiquitin Ligase TRIM67 Modulates Brain Development and Behavior

Specific class I members of the TRIM family of E3 ubiquitin ligases have been implicated in neuronal development from invertebrates to mammals. The single invertebrate class I TRIM and mammalian TRIM9 regulate axon branching and guidance in response to the axon guidance cue netrin-1, whereas mammalian TRIM46 establishes the axon initial segment. In humans, mutations in TRIM1 and TRIM18 are implicated in Optiz Syndrome, characterized by midline defects and often mild intellectual disability. TRIM67 is the most evolutionarily conserved vertebrate class I TRIM, yet is the least studied. Here we show that TRIM67 interacts with both its closest paralog TRIM9 and the netrin receptor DCC, and is differentially enriched in specific brain regions at specific developmental points. We describe the anatomical and behavioral consequences of deletion of murine Trim67. While viable, mice lacking Trim67 display severe impairments in spatial memory, cognitive flexibility, social novelty preference, muscle function and sensorimotor gating. Additionally, they exhibit abnormal anatomy of several brain regions, including the hippocampus, striatum and thalamus, as well as the corpus callosum. This study demonstrates the necessity for TRIM67 in appropriate brain development and function.\n\nSIGNIFICANCE STATEMENTAs a family, class I TRIM E3 ubiquitin ligases play important roles in neuronal development and function, potentially cooperatively. TRIM67 is the most evolutionarily conserved class I TRIM and is developmentally regulated and brain-enriched. Deletion of murine Trim67 results in malformations of a subset subcortical brain regions and of cortical and subcortical myelinated fiber tracts, as well as deficits in spatial memory, motor function, sociability and sensorimotor gating. We conclude that TRIM67 is critical for appropriate brain development and behavior, potentially downstream of the axon guidance cue netrin, and in cooperation with class I TRIM9.

neuroscience↗