CaMKII alpha 3 ' untranslated region-directed mRNA translocation in livingneurons: Visualization by GFP linkage

The CaMKII alpha mRNA extends into distal hippocampal dendrites, and the 3' untranslated region (3'UTR) is sufficient to mediate this localization. We labeled the 3'UTR of the CaMKII alpha mRNA in hippocampal cultures by usin g a green fluorescent protein (GFP)/MS2 bacteriophage tagging system. The C aMKII alpha 3'UTR formed discrete granules throughout the dendrites of tran sfected cells. The identity of the fluorescent granules was verified by in situ hybridization. Over 30 min time periods these granules redistributed w ithout a net increase in granule number; with depolarization there is a ten dency toward increased numbers of granules in the dendrites. These observat ions suggest that finer time resolution of granule motility might reveal ch anges in the motility characteristics of granules after depolarization. So that motile granules could be tracked, shorter periods of observation were required. The movements of motile granules can be categorized as oscillator y, unidirectional anterograde, or unidirectional retrograde. Colocalization of CaMKII alpha 3'UTR granules and synapses suggested that oscillatory mov ements allowed the granules to sample several local synapses. Neuronal depo larization increased the number of granules in the anterograde motile pool. Based on the time frame over which the granule number increased, the trans location of granules may serve to prepare the dendrite for mounting an adeq uate local translation response to future stimuli. Although the resident po ol of granules can respond to signals that induce local translation, the nu mber of granules in a dendrite might reflect its activation history.