Arc mRNA Docks Precisely at the Base of Individual Dendritic Spines Indicating the Existence of a Specialized Microdomain for Synapse-Specific mRNA Translation

Arc (aka Arg 3.1) is induced by neural activity and learning experience. Arc mRNA is rapidly exported into dendrites where it localizes near activated synapses. By imaging green fluorescent protein (GFP)-tagged mRNA in living neurons in culture, we show that fusion transcripts containing the Arc 3'UTR (untranslated region) localize with remarkable precision in a microdomain at the base of dendritic spines. Transcripts with the Arc 3'UTR that encode a reporter protein rather than Arc show precise localization. Localization persists in the presence of translation inhibitors, indicating that localization does not require ongoing translation. Similarly, polyribosome complexes remained stably positioned at spine bases in brain tissue treated with the translation inhibitor (puromycin) that releases ribosomes from mRNA. Single particle tracking revealed that Arc mRNA particles positioned at spine bases exhibited highly constrained submicron movements. These observations imply the existence of a microdomain at the spine base where Arc mRNA docks in association with a previously unknown mRNA-binding structural element. J. Comp. Neurol. 520:3105-3119, 2012. (C) 2012 Wiley Periodicals, Inc.