PROJECT SUMMARY Among different RNA species, circular RNAs (circRNAs) are particularly fascinating because they are highly resistant to degradation. This novel class of RNAs is expressed in a variety of eukaryotic organisms, in different cell types including neurons, and demonstrates conservation across mammals. Furthermore, they are regulated independently of their cognate linear isoforms. Mechanistically they can function as miRNA sponges, regulate splicing and transcription, bind to RNA binding proteins. Some circRNAs possess IRES and therefore could be translated. However, whether circRNAs play a critical role in long-term memory is unknown. Thus, a deep understanding of the contribution of circRNAs to LTM is expected to provide mechanistic insights and identify novel regulators of LTM. To this end, using contextual fear memory as a model for LTM, we have carried out an unbiased analysis of expression of circRNAss from the dentate gyrus (DG) subregion of the mouse hippocampus. Preliminary analysis of differentially expressed circRNAs in DG has resulted in the identification of three different circRNAs that are upregulated (padj<0.05) in fear-conditioned animals compared to context alone or shock alone controls. These results suggest that circRNAs are subjected to transcriptional changes during learning. The central hypothesis of this proposal is that the transcriptional changes in specific circRNAs in hippocampal subregions mediate the consolidation of contextual fear memory. To test this hypothesis, we here propose to carry out unbiased analysis of temporal regulation of circRNA expression in the tri-synaptic circuitry of the hippocampus following contextual fear conditioning, and functional dissection of differentially expressed circRNAs. We anticipate that successful completion of the experiments outlined in this proposal will unravel novel roles of circRNAs mechanisms in long-term memory storage.