Synapse Formation in the Zebrafish Spinal Cord

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Title: Synapse Formation in the Zebrafish Spinal Cord
Author: Easley-Neal, Courtney Nichelle, 1981-
Abstract: This dissertation describes research to elucidate the early steps in the process of synapse formation in the zebrafish spinal cord. One question is how presynaptic proteins are trafficked and recruited to nascent synapses. Previous work has suggested two possible models of presynaptic transport, either (1) most presynaptic proteins are transported together or (2) two types of transport packets, synaptic vesicle (SV) protein transport vesicles (STVs) and Piccolo-containing active zone precursor transport vesicles (PTVs), transport the necessary components separately. We tested these models using in vivo imaging in zebrafish spinal cord and found that the recruitment of at least three distinct transport packets during presynaptic assembly of a glutamatergic synapse occurs in an ordered sequence. First, STVs are stabilized at future synaptic sites, then PTVs, followed by a third transport packet type carrying Synapsin, a cytosolic protein that can tether SVs to actin. These results identify an order to the assembly of the presynaptic terminal in vivo, suggesting that a single synaptogenic interaction may precipitate the cascade of recruitment steps. We next examined the Cadm/SynCAM family of cell adhesion molecules, a family of proteins that has been shown to be able to induce synapse formation in vitro and was thought to play a role in recruitment of presynaptic proteins. As the role of these proteins in vivo was not well understood, we chose to examine the role of the cadms in zebrafish spinal cord. We found that zebrafish possess six cadm genes, and all are expressed throughout the nervous system both during development and in the adult. We then looked at the role of one of the Cadms, Cadm2a, in vivo in the zebrafish spinal cord. We found that knockdown of cadm2a significantly decreases the ability of zebrafish embryos to respond to touch. We also found that there is a significant reduction in the number of synapses, as shown by immunohistochemistry, formed between Rohon-Beard and CoPA neurons, the first two cell types in the touch response circuit. These data suggest that Cadm2a plays an important role in synapse formation in vivo. This dissertation contains both my previously published and unpublished co-authored material.
Description: xv, 102 p. : ill. (some col.)
Date: 2011-09

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