Identification and Analysis of Protein Complexes Mediating Synapse Formation

Thomas Biederer, Department of Neuroscience, Tufts University

Synapse formation is a decisive step in the development of neuronal networks. Alterations in this process affect synaptic plasticity, which is associated with changes in human behavior, learning, and addiction. Despite its importance for the central nervous system, only now the signals that initiate new synapses are being determined. Importantly, a synaptic adhesion molecule that induces new presynaptic terminals was recently identified. This protein, SynCAM 1, acts through homo- and heterophilic interaction of its extracellular domain across the synaptic cleft. Our objective is to identify the protein complexes that create pre- and postsynaptic specializations. The central hypothesis of this application is that SynCAM proteins induce the formation of presynaptic terminals. Our rationale is that this property will allow defining the protein complexes that assemble during synapse formation and maintenance. Using proteomic approaches, two specific aims will be pursued. First, the composition of synaptic plasma membranes under conditions of decreased synapse formation will be determined in genetically modified mouse models. Here, proteins signaling the induction of synapses are expected to be reduced in fractions of synaptic plasma membranes prepared from brains exhibiting impaired synaptogenesis, facilitating their identification. The SynCAM knockout mouse models required for these studies are available in our research group. This approach will determine the proteins that control synapse number and signal in synapse formation in the brain. Second, synaptic SynCAM adhesion complexes will be affinity-purified to identify their composition through proteomic approaches and to analyze their properties with biophysical techniques. This will yield insight into the molecular composition of synapse-organizing protein complexes.