Recent evidence implicates glutamatergic synapses as key pathogenic sites in psychiatric disorders. Common and rare variants in the ANK3 gene, encoding ankyrin-G, have been associated with bipolar disorder (BD), schizophrenia (SZ), autism spectrum disorders (ASD) and intellectual disability (ID). While a number of studies suggested that ankyrin-G plays a role in neuronal function beyond its well-characterized actions at the axon initial segment, its functions in mammalian glutamatergic synapses have not been investigated. Our preliminary studies show for the first time that ankyrin-G is integral to AMPAR-mediated synaptic transmission and to the maintenance of spine morphology. Using super-resolution microscopy we found that ankyrin-G forms distinct nanodomain structures within the spine head and neck. At these sites, it differentially modulates mushroom spine structure and function. Neuronal activity promotes ankyrin-G accumulation in distinct spine subdomains, where it differentially regulates activity-dependent spine structural plasticity. Our preliminary findings implicate subsynaptic nanodomains containing a major psychiatric risk molecule as having location- specific functions, and opens novel directions for basic and translational investigation of psychiatric risk molecules. The functions of ankyrin-G in spines of glutamatergic synapses in the brain have not yet been investigated. In this proposal we will use super-resolution and in vivo two-photon microscopy, in combination with biochemical, electrophysiological, molecular, and mouse model approaches, to test the hypotheses that different ankyrin-G isoforms play differential and integral roles in dendritic spine maintenance and glutamatergic synaptic transmission and plasticity. We will test these hypothesis in the following Aims: 1) Regulation of glutamatergic postsynaptic structure and function by ankyrin-G isoforms; 2) Mechanisms of regulation of postsynaptic ankyrin-G in spiny synapses; 3) Regulation of spiny synapse remodeling and function by ankyrin-G isoforms in the intact brain.