PROJECT SUMMARY / ABSTRACT Understanding the mechanisms that underlie learning and memory formation has been a goal of modern neuroscience. Moreover, investigating these processes is of critical importance to determine how they go awry in neurological disorders. Arc is an immediate early gene (IEG) that is dynamically expressed in response to learning and genetic ablation of this gene in rodents leads to severe long-term memory deficits. Recently, the Shepherd lab discovered that Arc evolved from an ancient Ty3 retrotransposon and has maintained its virus-like properties. In particular, Arc protein is capable of self-assembling into virus-like capsids that can encapsidate genetic material. These capsids can be transferred between neurons in extracellular vesicles (EVs) and deliver nucleic acids in the process, similar to retroviruses. However, the function of Arc mediated intercellular communication and the role of virus-like capsids in memory formation is entirely unknown. My current work has demonstrated that 1) Arc capsids are assembled and released from neurons during long-term potentiation (LTP) through direct interaction with I-BAR protein IRSp53. 2) EV transferred Arc reduces surface AMPA receptor levels via translation of delivered Arc mRNAs. Together, these results suggest that Arc mediates a novel form of intercellular synaptic plasticity through a virus-like signaling mechanism. The synaptic mechanisms of memory storage are poorly understood. Furthermore, why evolution exploited viral machinery to alter synaptic strength is unknown. This research plan will focus on how Arc’s virus-like properties have been co-opted to encode learned experiences and store information. To date, I have combined molecular and biochemical assays with various imaging techniques to elucidate how the Arc virus contributes to memory formation. I have used a novel Arc reporter system that dually labels both nascent Arc protein and mRNA to visualize Arc trafficking and release from living neurons during LTP. I have demonstrated that transferred Arc mRNA is translated in recipient neurons to induce AMPAR loss. The precise mechanisms governing how Arc virus-like signaling alters recipient cell function has yet to be determined. During the F99 phase, I propose to determine the intracellular trafficking and kinetics of Arc mediated viral signaling. In Aim 1.1, I will determine the intracellular trafficking of transferred Arc protein and mRNA. In Aim 1.2, I will determine the kinetics of transferred Arc EV uptake and AMPAR loss. During the K00 phase, I will study how activity-dependent release of extracellular vesicles alters the neuronal circuits that store memories. I hypothesize that neurons encoding learned experiences release EVs in an activity-dependent manner to shape the neuronal circuitry that will store memories. To test this, I will combine my current in vitro skillset with behavioral paradigms, the development of novel molecular tools, imaging techniques, ...