NON-IONOTROPIC NMDA RECEPTOR FUNCTIONS OF GLUN2B SHAPE EARLY CORTICAL DEVELOPMENT

Neurodevelopment depends on precisely coordinated molecular mechanisms that regulate neuronal migration, synaptogenesis, and circuit assembly. NMDA receptors (NMDARs) are central to these processes, yet their early developmental functions, particularly those independent of ion flux, remain poorly understood. This project investigates the role of the GluN2B subunit and its intracellular C-terminal domain (CTD) in early brain development. Developmental expression analyses using RT-PCR and public transcriptomic datasets reveal that GluN2B is expressed very early in the mouse cortex, with a sharp increase around birth, coinciding with peak synaptogenic periods. Using super-resolution STORM microscopy, we show that endogenous GluN2B-containing NMDARs form nanoscale membrane clusters in cortical neurons as early as DIV4, preceding the formation of excitatory synapses. Functional perturbation of GluN2B expression reduces synapse maturation in vitro, indicating a critical role for GluN2B in early circuit formation. We further analyzed a patient-derived truncating variant of the GluN2B CTD (Y1004*), associated with severe neurodevelopmental disorders with confocal and super-resolution microscopy techniques. Although these mutant receptors display normal surface expression and preserved ionotropic properties, they show altered membrane dynamics, reduced synaptic anchoring, and a redistribution toward extrasynaptic compartments. CTD truncation also induces conformational changes in the GluN1 subunit, consistent with impaired non-ionotropic NMDAR signaling. These findings identify GluN2B-dependent NMDAR clustering and CTD-mediated non-ionotropic signaling as key determinants of early neurodevelopment and highlight their relevance for GRIN-related disorders.