The SynCAM Family of Cell Adhesion Molecules Function Redundantly to Shape the Excitatory Synapse
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Functional characterization of synaptic proteins is often precluded by compensation not only among converging signaling pathways but also between structurally and functionally similar genes. One such gene family, the synaptic cell adhesion molecules (SynCAMs), contains four nearly identical members of which SynCAM1-3 are highly localized to excitatory synapses. SynCAMs have been demonstrated to have a clear synaptogenic potential when ectopically presented, either artificially or by overexpression, to developing neurons both in vitro and in vivo. Despite these observations, conflicting reports from gain- and loss-of-function experiments prevent the development of a cohesive functional model for SynCAMs in excitatory synapse formation. To overcome potential SynCAM functional redundancy and simultaneously compare effects of SynCAM knockdown and overexpression in cultured rat hippocampal neurons, I developed a tool for efficient multi-gene knockdown using artificial microRNAs. I then applied this tool with a novel analysis method which I call Mosaic Expression with Differentially Localized Reporters (MEDLR). Using MEDLR, I uncover novel synaptic phenotypes due to SynCAM1-3 knockdown which suggest SynCAM1-3 function redundantly through postsynapse-specific mechanisms to regulate excitatory synapse number and size. This dissertation contains both published and unpublished co-authored material.