Date of Award
Doctor of Philosophy (PhD)
Neurotransmission involves the release of neurotransmitters from a presynapticneuron, followed by the reuptake of the protein components of the synaptic vesicle. The basic steps of synaptic vesicle exocytosis and endocytosis have been elucidated, and a number of components of the neurotransmission machinery have been identified. The exact function of each component, however, has been difficult to ascertain as many components act in multiple steps of neurotransmission. In my thesis, I describe the identification of a mutation in the snt-1 gene, which encodes a member of the synaptotagmin family in Caenorhabditis elegans. Synaptotagmins are best known as the calcium-sensing proteins for regulated synaptic vesicle exocytosis. I examined the effects of this lesion on a number of sensory neurons and motor neurons, in order to ascertain the uniformity of the phenotype between different regions of the nervous system. I utilized known synaptic vesicle markers to visualize synaptic vesicle distribution and to quantify the effect of a snt-1 mutation in vivo. I found that snt-1 reduced synaptic clustering of the SV marker RAB-3 in multiple cell types. SNT-1 has previously been implicated in both exocytosis and endocytosis in GABAergic motor neurons of C. elegans. To extend these results, I examined the effect of SNT-1 on sensory neurons and used mutations to critically test the endocytosis-exocytosis model. To this end, I examined endocytosis and exocytosis mutants alone and in the snt-1 mutant background. Blocking exocytosis in the snt-1 mutant partially restores synaptic clustering of synaptic vesicle marker RAB-3. The suppression of the snt-1 mutant phenotype is consistent with SNT-1 playing a key role in endocytosis downstream of regulated exocytosis. The C. elegans genome contains seven identified synaptotagmin family members, of which only snt-1 has previously been studied. I characterized the phenotypes of null mutations of snt-2, snt-4, snt-5, and snt-6 in several sensory neurons, and found that some of the synaptotagmin family members affect synaptic vesicle distribution. The increased SV clustering in snt-2, snt-4, and snt- 5 mutants suggests that these synaptotagmins may promote SV exocytosis, inhibit endocytosis, or regulate the size of vesicle pools at the active zone. I also executed an analysis of a set of snt double mutants to determine which SNT family members were acting in shared or parallel pathways.
Winzenread, Laura, "An Analysis of Synaptotagmins in Caenorhabditis Elegans" (2013). Student Theses and Dissertations. 234.