Genetic analysis of a novel tubulin mutation that redirects synaptic vesicle targeting and causes neurite degeneration in C. elegans.
Neuronal cargos are differentially targeted to either axons or dendrites, and this polarized cargo targeting critically depends on the interaction between microtubules and molecular motors. From a forward mutagenesis screen, we identified a gain-of-function mutation in the C. elegans α-tubulin gene mec-12 that triggered synaptic vesicle mistargeting, neurite swelling and neurodegeneration in the touch receptor neurons. This missense mutation replaced an absolutely conserved glycine in the H12 helix with glutamic acid, resulting in increased negative charges at the C-terminus of α-tubulin. Synaptic vesicle mistargeting in the mutant neurons was suppressed by reducing dynein function, suggesting that aberrantly high dynein activity mistargeted synaptic vesicles. We demonstrated that dynein showed preference towards binding mutant microtubules over wild-type in microtubule sedimentation assay. By contrast, neurite swelling and neurodegeneration were independent of dynein and could be ameliorated by genetic paralysis of the animal. This suggests that mutant microtubules render the neurons susceptible to recurrent mechanical stress induced by muscle activity, which is consistent with the observation that microtubule network was disorganized under electron microscopy. Our work provides insights into how microtubule-dynein interaction instructs synaptic vesicle targeting and the importance of microtubule in the maintenance of neuronal structures against constant mechanical stress.
Institute of Molecular Medicine, College of Medicine, National Taiwan University, Taipei, Taiwan.
Jiun-Min
JM
Hsu
Institute of Molecular Medicine, College of Medicine, National Taiwan University, Taipei, Taiwan.
Chun-Hao
CH
Chen
Institute of Molecular Medicine, College of Medicine, National Taiwan University, Taipei, Taiwan.
Yen-Chih
YC
Chen
Electron Microscope Laboratory, University of California, Berkeley, Berkeley, California, United States of America.
Kent L
KL
McDonald
Department of Molecular and Cell Biology and Helen Wills Neuroscience Institute, University of California, Berkeley, Berkeley, California, United States of America.
Mark
M
Gurling
Department of Chemistry, National Taiwan University, Taipei, Taiwan.
Albert
A
Lee
Department of Molecular and Cell Biology and Helen Wills Neuroscience Institute, University of California, Berkeley, Berkeley, California, United States of America.
Gian
G
Garriga
Institute of Molecular Medicine, College of Medicine, National Taiwan University, Taipei, Taiwan.
Chun-Liang
CL
Pan
D000818:Animals; D017173:Caenorhabditis elegans; D029742:Caenorhabditis elegans Proteins / Q000235:genetics* / Q000378:metabolism; D003712:Dendrites / Q000235:genetics / Q000378:metabolism / Q000473:pathology; D004398:Dyneins / Q000378:metabolism; D005089:Exocytosis; D006801:Humans; D008870:Microtubules / Q000378:metabolism; D020125:Mutation, Missense; D009410:Nerve Degeneration / Q000235:genetics* / Q000473:pathology; D016501:Neurites / Q000378:metabolism / Q000473:pathology; D009435:Synaptic Transmission / Q000235:genetics*; D013572:Synaptic Vesicles / Q000235:genetics* / Q000378:metabolism; D014404:Tubulin / Q000235:genetics* / Q000378:metabolism
D029742:Caenorhabditis elegans Proteins; C118234:MEC-12 protein, C elegans; D014404:Tubulin; D004398:Dyneins