Regulators of Synaptic Vesicle Docking and Priming

Synaptic vesicle priming is dependent on the assembly of SNARE (soluble-N- ethylmaleimide-sensitive factor attachment receptor) complexes formed between Synaptobrevin, SNAP-25 and Syntaxin. The subsequent calcium-dependent release of primed vesicles requires the recruitment of the calcium-sensor, Synaptotagmin, a protein also implicated in endocytosis. As a consequence, proteins that regulate SNARE complex formation or stabilization can profoundly alter the synaptic strength. This thesis focuses on four SNARE interacting proteins, Snapin, Synaptotagmin, VPS- 39 as well as Tomosyn, and explores their neuronal function by primarily using high pressure freezing/ freeze substitution (HPF/FS) electron microscope (EM) combined with other techniques. Specifically, the results presented in this thesis establish that Snapin stabilizes the SNARE complex to promote fusion in a Synaptotagmin- independent manner in C. elegans, that C. elegans VPS-39 alters Syntaxin conformation to enable fusogenic SNARE complex assembly, and that Drosophila Tomosyn functions as an important effector in the cAMP signaling pathway.