Microtubule Supported Trafficking of Synaptic Vesicle Precursors and Recycling Synaptic Vesicles

Abstract

Synaptic Vesicles are critical components for synaptic communication in the nervous system. The proteins associated with synaptic vesicles that enable their functionality must be continuously produced, transported to necessary locations, and then eventually removed for degradation to ensure healthy function throughout the lifetime of the neuron. The microtubule cytoskeleton has long been known to support motion of many components within the cell, and filamentary actin has been shown to support local motion of synaptic vesicles between presynapses in an activity dependent manner. However, questions remained as to the level of microtubule-based synaptic vesicle motion.

This dissertation presents results showing the mechanistic effects of the microtubule cytoskeleton on axonal cargo, as microtubule ends must be navigated by synaptic vesicle precursors delivering vital synaptic vesicle proteins to the presynapse. Further, our results show that synaptic vesicles also utilize the microtubule cytoskeleton. This microtubule supported motion allows for directional differences in motion due to the microtubule polarization within the axon. Directional differences are observed near functioning presynapses, as recently recycled vesicles are less likely to be captured by a presynapse when moving at higher speeds towards the cell body. A model of motion including differential capture probability among vesicles supported by different cytoskeletal networks is laid out and shown to support a net retrograde flux that supports healthy turnover of synaptic vesicle proteins.

Chapter 2 provides background information on the biological elements and concepts underlying my research. This presents essential topics needed to understand what was studied, the results of the experiments, and the context of the results within the larger landscape of research. Chapter 3 then sets the stage with open questions in the field upon which my research sheds new light. Chapter 4 explains the methods and materials used to experimentally study synaptic vesicles and synaptic vesicle precursors. This chapter will build on the background information provided with specific information about how these elements are studied. Chapter 5 contains the experimental results and computational models based on those results. Finally, Chapter 6 contains discussion of the results, as well as an extended discussion of their meaning within the larger context of the field, along with further questions yet to be answered.