Regulation of Axon Transport by Tubulins in Caenorhabditis elegans
Date Issued
2012
Date
2012
Author(s)
Hsu, Jiun-Min
Abstract
Microtubules play essential functions in axon transport by serving as tracks for motor proteins and their cargos. They also play a more active role by directing cargo transport through tubulin posttranslational modification. Here we propose yet another level of regulation: specific residues on tubulins directly regulate synaptic vesicle transport by binding motor proteins with differential affinities. The C. elegans gene mec-12 encodes an α-tubulin that is uniquely enriched in the six touch receptor neurons. Complete loss of mec-12 causes loss of synaptic vesicles at synaptic regions and their accumulation in neuronal cell bodies. We identified a missense mutation of mec-12, gm379, which not only prevents synaptic vesicles from reaching synaptic regions, but also redirects them to non-axon compartment of the PLM touch neuron (synaptic vesicle mistargeting). This mutation also triggered extensive axon blebbing in the touch neurons. gm379 alters a conserved C-terminus glycine residue and behaves as a neomorphic gain-of-function mutation, as axon blebbing and synaptic vesicle mistargeting were not seen in the mec-12 null and could be completely abolished by mec-12 RNAi. Immunostaining for various microtubule posttranslational modifications revealed no obvious changes in the gm379 mutant, and synaptic vesicle mistargeting was not seen after RNAi knockdown of genes encoding enzymes for microtubule posttranslational modifications. Interestingly, reducing UNC-104/Kinesin 3/KIF1A functions aggravated vesicle mistargeting, and excess UNC-104 partially rescued it. By contrast, elimination of dynein heavy chain DHC-1 partially suppressed synaptic vesicle defects in gm379, mimicking the effects of UNC-104 overexpression. The glycine residue mutated in gm379 resides in an exposed helix-loop region on the tubulin polymers, which had been shown to be a common binding site for KIF1A and dynein heavy chain. We hypothesize that gm379 switches motor binding affinity of microtubules towards dynein, resulting in transport defects and mistargeting of synaptic vesicles.
Subjects
Axon transport
kinesin
dynein
C. elegans
microtubule
Type
thesis
File(s)![Thumbnail Image]()
Loading...
Name
ntu-101-R99448010-1.pdf
Size
23.32 KB
Format
Adobe PDF
Checksum
(MD5):9e1d3c235c87132416bf8515d8ad012c