Yogev, Shaul et al. (2017) International Worm Meeting "Local inhibition of microtubule dynamics by dynein is required for neuronal cargo distribution."

Yogev, Shaul, Maeder, Celine, Shen, Kang

[International Worm Meeting, 2017]

Microtubules (MTs) are the main cytoskeletal substrate on which axonal transport progresses. How the architecture and dynamics of the MT network affect the transport of neuronal cargo is poorly understood. Furthermore, molecular motors not only carry cargoes but also regulate MT behaviour, and the mechanisms underlying this regulation, and their role in vivo, are not clear. We developed a rapid, fluorescence-based method for analyzing neuronal MT length, abundance and dynamics in C. elegans, and used it to explore how neuronal MTs are patterned and how these patterns affect cargo transport. We identified a surprising function for dynein heavy chain (DHC-1), in setting polymer distribution and dynamics in the DA9 dendrite. In disease-mimicking dhc-1 alleles, MT length and abundance were normal, but polymers were shifted distally, and excessive growth and collapse occurred at the dendrite tip, resulting in the formation of aberrant MT loops. dhc-1 mutants also accumulated neuronal cargo at the tip of the dendrite, leading to severely reduced availability of mitochondria and synaptic vesicle precursors in normal locations. Strikingly, cargo mis-localization is not due to defects in dynein's function as a motor in cargo transport, but to its role in locally suppressing MT dynamics. Unstable looping MTs acted as cargo traps, and cargo could be restored to its endogenous sites by suppressing MT dynamics. Live imaging of axonal transport, mutant analysis and single molecule in-vitro assays suggest a model wherein an anchored dynein pool at the tip of the dendrite interacts with plus-end-out MTs to stabilize them and allow efficient retrograde transport. These results identify functional significance for neuronal MT stability and suggest a mechanism for cellular dysfunction in dynein-linked disease.

Yogev, Shaul et al. (2013) International Worm Meeting "Suppression of microtubules dynamics by DHC-1 is required for an intact cytoskeleton and efficient cargo trafficking in C. elegans dendrites."

Shen, Kang, Yogev, Shaul

[International Worm Meeting, 2013]

A hallmark of neuronal microtubules (MTs) is their stable, non-dynamic character. Yet how this stability is achieved, or what purpose it serves is not well understood. Here we show that Dynein Heavy Chain 1 (DHC-1), the main subunit of the cytoplasmic dynein retrograde motor is required to suppress MT dynamics in the dendrites of C. elegans neurons. In the absence of dhc-1, dendritic MTs are more dynamic, suggesting that their stability is decreased. Accordingly, MTs fail to fully support dendrite elongation, leading to shorter processes. More dramatically, dynamic "plus end out" MTs fail to stop at the distal dendrite tip in dhc-1 mutants, and instead loop backwards, giving rise to aberrant cytoskeletal structures. Cargo is not correctly transported through these structures, and accumulates as large ectopic puncta. Previous studies have shown that cargo accumulation at axonal tips in dhc-1 mutants is a consequence of impaired retrograde transport. However, our data indicate that the dendritic dhc-1 phenotypes are not due to a failure in minus-end directed transport. Instead, we show evidence for a model in which cortically anchored DHC-1 captures MTs, thereby stabilizing them. This capture and stabilization couples MT growth to dendrite growth, and yields a straight cytoskeleton on which cargo can be smoothly transported. Thus, our results provide both a mechanism for ensuring a stable MT cytoskeleton in dendrites and illustrate its biological significance.