A role for dendritic translation of CaMKIIα mRNA in olfactory plasticity.

Local protein synthesis in dendrites contributes to the synaptic modifications underlying learning and memory. The mRNA encoding the α subunit of the calcium/calmodulin dependent Kinase II (CaMKIIα) is dendritically localized and locally translated. A role for CaMKIIα local translation in hippocampus-dependent memory has been demonstrated in mice with disrupted CaMKIIα dendritic translation, through deletion of CaMKIIα 3'UTR. We studied the dendritic localization and local translation of CaMKIIα in the mouse olfactory bulb (OB), the first relay of the olfactory pathway, which exhibits a high level of plasticity in response to olfactory experience. CaMKIIα is expressed by granule cells (GCs) of the OB. Through in situ hybridization and synaptosome preparation, we show that CaMKIIα mRNA is transported in GC dendrites, synaptically localized and might be locally translated at GC synapses. Increases in the synaptic localization of CaMKIIα mRNA and protein in response to brief exposure to new odors demonstrate that they are activity-dependent processes. The activity-induced dendritic transport of CaMKIIα mRNA can be inhibited by an NMDA receptor antagonist and mimicked by an NMDA receptor agonist. Finally, in mice devoid of CaMKIIα 3'UTR, the dendritic localization of CaMKIIα mRNA is disrupted in the OB and olfactory associative learning is severely impaired. Our studies thus reveal a new functional modality for CaMKIIα local translation, as an essential determinant of olfactory plasticity.