INVESTIGATING THE RELATIONSHIP BETWEEN THE ORGANIZATION OF THE MICROTUBULE CYTOSKELETON AND THE REGENERATIVE PROPERTIES OF NEURONS IN ATYPICAL CASES OF COMPOSITION AND DAMAGE.
Open Access
- Author:
- Shorey, Matthew
- Graduate Program:
- Molecular, Cellular, and Integrative Biosciences
- Degree:
- Doctor of Philosophy
- Document Type:
- Dissertation
- Date of Defense:
- August 20, 2021
- Committee Members:
- Melissa Rolls, Chair & Dissertation Advisor
Richard Ordway, Outside Unit & Field Member
Wendy Hanna-Rose, Major Field Member
Joyce Jose, Major Field Member
Melissa Rolls, Program Head/Chair - Keywords:
- Axon regeneration
Microtubule organization
Zebrafish
Dendrite regeneration
DRG regeneration - Abstract:
- Sensory neurons are irreplaceable cells that suffer damage that is both frequent and unavoidable. As such the ability of sensory neurons to regenerate is inseparable from maintenance of the sensory system that is necessary for normal function. The goal of this study is to gain additional insight into the characteristics of sensory neurons so as to be able to better anticipate their responses to damage, with the long-term goal of potentially improving regenerative outcomes. While previous work has shown that axon and dendrites rely upon different pathways to regenerate after injury, I have taken this a step further to demonstrate that not only are these pathways separate, but that they are seemingly independent can operate concurrently without interference with each other. After laser -based removal of all neurites, DA (dendritic arborization) neurons were able to regenerate distinct axonal and dendritic compartments, with proper morphology, microtubule polarity, and localization of a known neurite specific marker. This shows that data showing several types of neurons demonstrate axon injury is toxic to the dendritic arbor, that nothing is inherently compatible about the pathways governing their regeneration. I have answered questions left by previous work about the microtubule polarity of the sensory arbor of DRG sensory neurites. I have performed an optical in-vivo characterization of the microtubule polarity of intact zebrafish DRG sensory neurites and found them to have completely uniform axonal polarity throughout their entire length. I have also demonstrated the possibility that neurons with uniform plus-end-out polarity in all neurites can maintain a centralized MTOC at a developmental timepoint long after neurons with mixed polarity dendrites would be expected to have eliminated theirs, and that this is the case across multiple cell types and distant species relations. I have also shown evidence for the use of polymerizing microtubule iv minus ends as being relevant in the organization of the cytoskeleton of mature DRG sensory neurites. Axons regenerate via a molecular pathway that is conserved across both species and cell type. I have established that despite an unambiguous axonal microtubule polarity, that DRG sensory neurites in fish regenerate by a pathway that functions even with homozygous loss of function mutations to the DLK and LZK genes, which in the same species has been shown to be sufficient to abrogate motor neuron axon regeneration. In summary, I have established that the pathways by which axons and dendrites regenerate are orthogonal to each other, as well as answered decades old questions about the cytoskeletal composition of DRG sensory neurites, and shown a potential exception to the accepted model by which neurons organize their microtubule cytoskeletons and further shown that axonal microtubule polarity is not necessarily indicative of dependence on the classic axon regeneration pathway for neurites to recover after injury.