Microtubule-dependent recruitment of Staufen-Green fluorescent protein into large RNA-containing granules and subsequent dendritic transport in living hippocampal neurons

Dendritic mRNA transport and local translation at individual potentiated sy napses may represent an elegant way to form synaptic memory. Recently, we c haracterized Staufen, a double-stranded RNA-binding protein, in rat hippoca mpal neurons and showed its presence in large RNA-containing granules, whic h colocalize with microtubules in dendrites. in this paper, we transiently transfect hippocampal neurons with human Staufen-green fluorescent protein (GFP) and find fluorescent granules in the somatodendritic domain of these cells. Human Stau-GFP granules show the same cellular distribution and size and also contain RNA, as already shown for the endogenous Stau particles. In time-lapse videomicroscopy, we show the bidirectional movement of these Staufen-GFP-labeled granules from the cell body into dendrites and vice ver sa. The average speed of these particles was 6.4 mu m/min with a maximum ve locity of 24.3 mu m/min. Moreover, we demonstrate that the observed assembl y into granules and their subsequent dendritic movement is microtubule depe ndent. Taken together, we have characterized a novel, nonvesicular, microtu bule-dependent transport pathway involving RNA-containing granules;with Sta ufen as a core component. This is the first demonstration in living neurons of movement of an essential protein constituent of the mRNA transport mach inery.