Caldendrin Directly Couples Postsynaptic Calcium Signals to Actin Remodeling in Dendritic Spines

Compartmentalization of calcium-dependent plasticity allows for rapid actin remodeling in dendritic spines. However, molecular mechanisms for the spatio-temporal regulation of filamentous actin (F-actin) dynamics by spinous Ca2+-transients are still poorly defined. We show that the postsynaptic Ca2+ sensor caldendrin orchestrates nano-domain actin dynamics that are essential for actin remodeling in the early phase of long-term potentiation (LTP). Steep elevation in spinous [Ca2+]i disrupts an intramolecular interaction of caldendrin and allows cortactin binding. The fast on and slow off rate of this interaction keeps cortactin in an active conformation, and protects F-actin at the spine base against cofilin-induced severing. Caldendrin gene knockout results in higher synaptic actin turnover, altered nanoscale organization of spinous F-actin, defects in structural spine plasticity, LTP, and hippocampus-dependent learning. Collectively, the data indicate that caldendrin-cortactin directly couple [Ca2+]i to preserve a minimal F-actin pool that is required for actin remodeling in the early phase of LTP. •Calcium binding relieves intra-molecular inhibition of caldendrin•Caldendrin binding activates cortactin and promotes F-actin stabilization in spines•Caldendrin depletion results in loss of stable F-actin and spine plasticity deficits•Caldendrin directly couples [Ca2+]i to the stabilization of F-actin in synapses Activity-dependent remodeling of the actin cytoskeleton is essential for synaptic plasticity. Mikhaylova et al. describe a novel molecular mechanism directly translating the initial calcium influx into coordinated rearrangement of spinous actin filaments at the nanoscale in dendritic spines.