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Title

The Role of Cytoskeletal Stability in Regulating Synapse Development and Axonal Regeneration through the DLK Pathway

Date of Award

Spring 5-15-2014

Author's School

Graduate School of Arts and Sciences

Author's Department

Biology & Biomedical Sciences (Neurosciences)

Degree Name

Doctor of Philosophy (PhD)

Degree Type

Dissertation

Abstract

Proper network information processing relies on the intact axonal and synaptic function. In this work we investigate the mechanisms regulating the formation of the synapse and axonal response to injury.

During development, neurons send out axons to connect them to their distal targets. The formation of the synapse, a point of contact between the two functional units of the nervous system, is regulated by an array of genes, many of which remain unknown. Through a large-scale RNAi screen we have identified a large number of novel genes that are involved in regulating different aspects of synapse development. By separating the genes based on their function and correlating them to the phenotype that they cause we have identified a number of genes with a shared function that are involved in a particular aspect of synapse development. Notably, genes for proteasome subunits and mitotic spindle organizers are enriched in those causing defects in synaptic apposition and NMJ stability.

Genes that are involved in synapse development often also play a role in other aspects of neuronal function. We pursued the function of one particular gene that is involved in synapse development, short stop. We identify a novel allele of short stop which does not cause embryonic lethality and allows us to study the role that short stop plays in synaptic development. Mutants for short stop have a striking synapse overgrowth. This synapse phenotype is caused by the upregulation of the dual leucine zipper kinase (DLK) pathway, a MAP3K known for its role in synapse development and axon regeneration. We hypothesize that the molecular function of Short Stop as an actin-microtubule cross-linker is responsible for the DLK pathway activation in the mutant. To support this model we demonstrate that knock down of the subunits of the TCP1 complex, a chaperonin that folds actin and microtubules, also results in the upregulation of the DLK pathway. These data lead us to propose that cytoskeleton destabilization is a mechanism of DLK pathway activation. We further show that activation of this pathway in the short stop mutant is sufficient to enhance axonal response to injury.

Although the DLK pathway is a key regulator of the axonal injury response, it is still unclear how this pathway is activated during injury. We demonstrate that the DLK pathway can be activated by pharmacological disruption of the cytoskeleton, which also happens during a traumatic injury. This new mechanism allows us to manipulate the DLK pathway in the intact neuron and test the sufficiency of this pathway in axonal regeneration response. We show that activating the DLK pathway via pharmacological destabilization of the cytoskeleton is sufficient to enhance axonal regeneration after injury. These data establish a new mechanism of the DLK pathway activation and that the DLK pathway is not only required but also sufficient to turn on a pro-regenerative state in an uninjured neuron.

Language

English (en)

Chair and Committee

Aaron DiAntonio

Committee Members

Gerhild Scholz Williams, Steven Mennerick, Paul H Taghert, Valeria Cavalli, Michael Nonet

Comments

Permanent URL: https://doi.org/10.7936/K7J67DWJ

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