Recombinant Probes Reveal Dynamic Localization of CaMKIIα within Somata of Cortical Neurons

In response to NMDA receptor stimulation, CaMKII alpha moves rapidly from a diffuse distribution within the shafts of neuronal dendrites to a clustered postsynaptic distribution. However, less is known about CaMKII alpha localization and trafficking within neuronal somata. Here we use a novel recombinant probe capable of labeling endogenous CaMKII alpha in living rat neurons to examine its localization and trafficking within the somata of cortical neurons. This probe, which was generated using an mRNA display selection, binds to endogenous CaMKII alpha at high affinity and specificity following expression in rat cortical neurons in culture. In similar to 45% of quiescent cortical neurons, labeled clusters of CaMKII alpha 1-4 mu m in diameter were present. Upon exposure to glutamate and glycine, CaMKII alpha clusters disappeared in a Ca2+-dependent manner within seconds. Moreover, minutes after the removal of glutamate and glycine, the clusters returned to their original configuration. The clusters, which also appear in cortical neurons in sections taken from mouse brains, contain actin and disperse upon exposure to cytochalasin D, an actin depolymerizer. In conclusion, within the soma, CaMKII localizes and traffics in a manner that is distinct from its localization and trafficking within the dendrites.