Regulation of Memory by the microRNA/RISC Pathway

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PROJECT SUMMARY/ABSTRACT One of the remaining mysteries of neuroscience is how memories are stored for periods of days, weeks or years. It has been known for some time that the formation of stable memory requires protein synthesis, a feature of memory common to vertebrates and invertebrates. Protein synthesis localized to the synapse is of special interest because it might confer selective synaptic change and the stable modification of a neural circuit. But how protein synthesis is deployed across the nervous system and contributes to the formation of a particular memory is unclear. We have used fluorescent reporter constructs to visualize synaptic protein synthesis in Drosophila that form a long-term memory. The association of an odor with electric shock was correlated with local protein synthesis that displayed features of synaptic specificity, and the induction of mRNA transport to synaptic regions. These features of memory appeared to be controlled by the RNA- Induced Silencing Complex (RISC) in a pathway involving RISC regulation by the Proteasome. A RISC component, Armitage, was found to be ubiquitinated and degraded in a Proteasome-dependent fashion, evidently contributing to the release of synaptic protein synthesis from RISC suppression. These observations raise a number of questions of importance to understanding the mechanisms underlying memory. Can we build a fine-grained neural map of where protein synthesis occurs as a particular memory forms? Can we build a map of where the regulation of protein synthesis is required? What are the temporal characteristics of synaptic protein synthesis and how are they related to the maintenance of a synapse in a stable new state? We have only begun to understand the role and biochemistry of the RISC pathway at the synapse, but as an evident regulator of these events, we believe this understanding will illuminate the biochemical and cellular mechanisms underlying memory. The strong potential of this study to make clinical contributions should not be overlooked, as it is evident that these mechanisms operate at mammalian and human synapses. This study will likely identify new targets for therapeutic efforts to aid patients with disorders of memory (for example, Alzheimer's Disease) and synaptic activity (for example, epilepsy).