The dynamic turnover and functional roles of α-actinin in dendritic spines

Abstract

Excitatory synapses are located on actin-rich protrusions known as dendritic spines. α-Actinin is an actin binding protein enriched in the postsynaptic density (PSD) of excitatory synapses. Because it also binds to NMDA receptors and other PSD components, α-actinin has been proposed to link NMDA receptors and the PSD to the underlying actin cytoskeleton of the dendritic spine. Although α-actinin has been implicated in modulation of NMDA receptor activity, the cell biological function of α-actinin in neurons is unknown. We report here that α-actinin is concentrated in spines. Both the actin binding domain and the spectrin repeat region (which interacts with NMDA receptors) of α-actinin2 are required for spine targeting. In live imaging experiments, Venus-tagged α-actinin2 in dendritic spines showed faster turnover than PSD-95, as determined by fluorescent recovery after photobleaching (FRAP), and individual spines often showed marked fluctuations in α-actinin content over a time-scale of minutes. Overexpression of α-actinin2 increased the length and density of dendritic protrusions in cultured hippocampal neurons, an effect that requires the actin binding domain and the spectrin repeats of α-actinin. These results suggest that α-actinin regulates spine morphology and density.