Compensatory redistribution of neuroligins and N-cadherin following deletion of synaptic β1-integrin

Abstract

β1‐containing integrins are required for persistent synaptic potentiation in hippocampus and regulate hippocampal‐dependent learning. Based largely on indirect evidence, there is a prevailing assumption that β1‐integrins are localized at synapses, where they contribute to synapse adhesion and signaling, but this has not been examined directly. Here we investigate the fine localization of β1‐integrin in adult mouse hippocampus using high‐resolution immunogold labeling, with a particular emphasis on synaptic labeling patterns. We find that β1‐integrins localize to synapses in CA1 and are concentrated postsynaptically. At the postsynaptic membrane, β1‐integrins are found more commonly clustered near active zone centers rather than at the peripheral edges. In mice harboring a conditional deletion of β1‐integrins, labeling for N‐cadherin and neuroligins increases. Western blots show increased levels of N‐cadherin in total lysates and neuroligins increase selectively in synaptosomes. These data suggest there is a dynamic, compensatory adjustment of synaptic adhesion. Such adjustment is specific only for certain cell adhesion molecules (CAMs), because labeling for SynCAM is unchanged. Together, our findings demonstrate unequivocally that β1‐integrin is an integral synaptic adhesion protein, and suggest that adhesive function at the synapse reflects a cooperative and dynamic network of multiple CAM families. J. Comp. Neurol. 520:2041–;2052, 2012. © 2011 Wiley Periodicals, Inc.