β-Catenin regulates excitatory postsynaptic strength at hippocampal synapses

The precise contribution of the cadherin–␤-catenin synapse adhe- sion complex in the functional and structural changes associated with the pre- and postsynaptic terminals remains unclear. Here we report a requirement for endogenous ␤-catenin in regulating synaptic strength and dendritic spine morphology in cultured hippocampal pyramidal neurons. Ablating ␤-catenin after the ini- tiation of synaptogenesis in the postsynaptic neuron reduces the amplitude of spontaneous excitatory synaptic responses without a concurrent change in their frequency and synapse density. The normal glutamatergic synaptic response is maintained by postsyn- aptic ␤-catenin in a cadherin-dependent manner and requires the C-terminal PDZ-binding motif of ␤-catenin but not the link to the actin cytoskeleton. In addition, ablating ␤-catenin in postsynaptic neurons accompanies a block of bidirectional quantal scaling of glutamatergic responses induced by chronic activity manipulation. In older cultures at a time when neurons have abundant dendritic spines, neurons ablated for ␤-catenin show thin, elongated spines and reduced proportion of mushroom spines without a change in spine density. Collectively, these findings suggest that the cad- herin–␤-catenin complex is an integral component of synaptic strength regulation and plays a basic role in coupling synapse function and spine morphology.