Developmental remodeling shapes neural circuits via activity-dependent pruning of synapses and axons. Regulation of the cytoskeleton is critical for this process, as microtubule loss via enzymatic severing is an early step of pruning across many circuits and species. However, how microtubule-severing enzymes, such as spastin, are activated in specific neuronal compartments remains unknown. Here, we reveal that polyglutamylation, a post-translational tubulin modification enriched in neurons, plays an instructive role in developmental remodeling by tagging microtubules for severing. Motor neuron-specific gene deletion of enzymes that add or remove tubulin polyglutamylation-TTLL glutamylases vs. CCP deglutamylases-accelerates or delays neuromuscular synapse remodeling in a neurotransmission-dependent manner. This mechanism is not specific to peripheral synapses but also operates in central circuits, e.g., the hippocampus. Thus, tubulin polyglutamylation acts as a cytoskeletal rheostat of remodeling that shapes neuronal morphology and connectivity.

• MeSH
• Hippocampus metabolism   cytology   MeSH
• Polyglutamic Acid * metabolism   MeSH
• Microtubules * metabolism   MeSH
• Motor Neurons * metabolism   MeSH
• Mice MeSH
• Neuromuscular Junction metabolism   MeSH
• Synaptic Transmission MeSH
• Neurons * metabolism   MeSH
• Neuronal Plasticity * physiology   MeSH
• Peptide Synthases metabolism   genetics   MeSH
• Protein Processing, Post-Translational MeSH
• Spastin metabolism   MeSH
• Synapses metabolism   MeSH
• Tubulin metabolism   MeSH
• Animals MeSH
• Check Tag
• Mice MeSH
• Animals MeSH
• Publication type
• Journal Article MeSH
• Names of Substances
• Polyglutamic Acid * MeSH
• Peptide Synthases MeSH
• Spastin MeSH
• tubulin polyglutamylase MeSH Browser
• Tubulin MeSH

Microtubule doublets (MTDs) comprise an incomplete microtubule (B-tubule) attached to the side of a complete cylindrical microtubule. These compound microtubules are conserved in cilia across the tree of life; however, the mechanisms by which MTDs form and are maintained in vivo remain poorly understood. Here, we identify microtubule-associated protein 9 (MAP9) as an MTD-associated protein. We demonstrate that C. elegans MAPH-9, a MAP9 homolog, is present during MTD assembly and localizes exclusively to MTDs, a preference that is in part mediated by tubulin polyglutamylation. We find that loss of MAPH-9 causes ultrastructural MTD defects, including shortened and/or squashed B-tubules with reduced numbers of protofilaments, dysregulated axonemal motor velocity, and perturbed cilia function. Because we find that the mammalian ortholog MAP9 localizes to axonemes in cultured mammalian cells and mouse tissues, we propose that MAP9/MAPH-9 plays a conserved role in regulating ciliary motors and supporting the structure of axonemal MTDs.

• Keywords
• C. elegans, MAP9, axoneme, cilia, dynein, kinesin, microtubule, microtubule doublet, microtubule-associated protein, polyglutamylation,
• MeSH
• Axoneme * metabolism   ultrastructure   MeSH
• Caenorhabditis elegans * metabolism   MeSH
• Cilia metabolism   MeSH
• Microtubules metabolism   MeSH
• Mice MeSH
• Movement MeSH
• Mammals MeSH
• Tubulin metabolism   MeSH
• Animals MeSH
• Check Tag
• Mice MeSH
• Animals MeSH
• Publication type
• Journal Article MeSH
• Research Support, Non-U.S. Gov't MeSH
• Research Support, N.I.H., Extramural MeSH
• Names of Substances
• Map9 protein, mouse MeSH Browser
• Tubulin MeSH