Activity-dependent dendritic translation in CNS neurons is important for the synapse-specific provision of proteins that may be necessary for strengthening of synaptic connections. A major rate-limiting factor during protein synthesis is the availability of eukaryotic translation initiation factor 4E (eIF4E), an mRNA 5'-cap-binding protein. In this study we show by fluorescence in situ hybridization (FISH) that the mRNA for eIF4E is present in the dendrites of cultured rat hippocampal neurons. Under basal culture conditions, 58.7 +/- 11.6% of the eIF4E mRNA clusters localize with or immediately adjacent to PSD-95 clusters. Neuronal activation with KCl (60 mM, 10 min) very significantly increases the number of eIF4E mRNA clusters in dendrites by 50.1 and 74.5% at 2 and 6 h after treatment, respectively. In addition, the proportion of eIF4E mRNA clusters that localize with PSD-95 increases to 74.4 +/- 7.7% and 77.8 +/- 7.6% of the eIF4E clusters at 2 and 6 h after KCl treatment, respectively. Our results demonstrate the presence of eIF4E mRNA in dendrites and an activity-dependent increase of these clusters at synaptic sites. This provides a potential mechanism by which protein translation at synapses may be enhanced in response to synaptic stimulation.
Animals ; Cells, Cultured ; Dendrites/*metabolism ; Eukaryotic Initiation Factor-4E/genetics/*metabolism ; Hippocampus/*cytology ; Immunohistochemistry ; In Situ Hybridization, Fluorescence ; Microscopy, Confocal ; Neurons/cytology/*physiology ; Potassium Chloride/pharmacology ; Protein Biosynthesis ; RNA, Messenger/genetics/*metabolism ; Rats ; Rats, Sprague-Dawley ; Synapses ; *Up-Regulation