Understanding the effect of tubulin post‐translational modifications on axonal transport in C. elegans

Abstract

A remarkable number of post-translational modifications (PTMs) on tubulin and microtubules (MTs) have been identified that affect MT dynamic, stability, organization and its interaction with motor proteins (such as kinesin and dynein) in neurons. Given the different types of PTMs in neurons and their roles in neuronal function, we emphasize on and investigate the role of three different PTMs glutamylation, tyrosination, and acetylation on axonal transport of UNC-104 (kinesing-3/KIF1A) and its cargo RAB-3 in C. elegans. Dysfunctional axonal transport has a large impact on synaptic transmission affecting memory and synaptic plasticity often leading to neurological disorders.We use a diverse set of tools such as motor motility assays, in situ immunostaining, co-immunoprecipitation assays etc. as well as in vivo protein-interaction assays (BiFC) to dissect the role of these PTMs. Here, I am reporting that in polyglutamulase mutants (TTLL-11) worm's velocities and run lengths of both UNC-104 and its cargo RAB-3 were significantly reduced as compared to wildtype. Further, we confirmed the reduction of tubulin polyglutamylation in worm lysates after TTLL-11 knockout consistent with reduced fluorescence in whole mount staining using Poly E GT335( sigma) antibodies. On the other hand, knocking out deglutamylase CCPP-1 does neither affect speeds nor run lengths for both motor and its cargo. Interestingly, I also observed that UNC-104 interacts with glutamylase enzymes in ccpp-1 mutant worm lysates when employing in co-IP assays. Additionally, I observed that in worms carrying a mutation in tyrosine ligase TTLL-12, kinesin-3 UNC-104 and its cargo RAB-3 exhibit reduced velocity, run lengths, less directional changes and increased pausing times compared to wildtype. Similarly, in acetylation mutant worm's mec-17 the velocity and run lengths of both UN-104 and its cargo RAB-3 were also significantly reduced consistent with observations on kinesin-1 by others.Therefore, based on above results, we hypothesize that these changes in axonal transport efficiencies are related to differentially post-translational modified tubulins. Unraveling the tubulin code in the nervous system will lead the new insights how cargo transport (which is tightly related to neuronal function and viability) is regulated by a new type of mechanism. We believe that our basic research will provide important mechanistic insights important for drug design to prevent or cure neuronal diseases such as tubulinopathies.