The intracellular signaling mechanisms instructing synapse development remain incompletely understood. Our work has shown that SynCAMs have signaling roles and we are elucidating these pathways. Analyzing synaptic changes in vivo, we have applied proteomic studies of synapses in mouse models with altered synaptogenesis to dissect signaling pathways. One example is our identification of the GTPase activator Farp1 as a novel postsynaptic protein that acts downstream of SynCAM adhesion and Semaphorin/Plexin signaling to promote synapse number and dendrite differentiation. We continue to elucidate how signaling pathways are integrated to control dendrite and synapse development.