Translation of dendritic mRNA following global and focal induction of long-term potentiation.

Abstract

Long-term potentiation (LTP) is the biological basis for learning and memory. In the hippocampus, LTP can be induced readily and maintained for hours to weeks. The persistent phase of LTP in hippocampal CA1 neurons requires protein synthesis. Some mRNAs are transported into dendrites, where an inhibitory complex containing the proteins CPEB and 4E-BP1 prevents their translation until intracellular signals cause the complex to unbind, allowing protein synthesis to proceed. Although many dendritic mRNAs have been identified, the time course and biochemical mechanism of translation initiation remains unclear. I hypothesized that dendritically repressed mRNAs are translated in the dendrites of CA1 neurons following a globally delivered LTP-inducing stimulus. I created a fluorescent reporter molecule and showed that chemical means of inducing LTP caused a rapid and transient increase in dendritic protein synthesis, dependent on CPEB binding and 4E-BP1 activation, and prevented by NMDA receptor antagonists and translation inhibitors anisomycin or rapamycin. I then focused on the spatial profile of translation relative to the site of LTP initiation. I hypothesized that, when a single spine receives a stimulus sufficient to induce late phase LTP, new protein and phosphorylated intracellular mediators would be observed only in the stimulated spine. I used microphotolysis of caged glutamate in an attempt to induce spine-specific LTP and created a second, novel reporter construct with limited diffusion to test this hypothesis. Unfortunately, these attempts were unsuccessful. Nevertheless, my findings support the idea that induction of LTP triggers de-repression of dendritic mRNAs and dendritic synthesis of new proteins.