Although a large number of experiences produce transient memory only some of them form stable long-term memory. The value of the experience and internal state of the organism plays an important role in determining this transition from short-term to long-term memory. However, how external experience and the internal state of the organism interact at a molecular level to influence memory storage is largely unknown. The synthesis of new proteins is required to form stable long-term memory. CPEB, a family of RNA-binding proteins, regulate activity-dependent protein synthesis in the neuron. In Aplysia, a specific CPEB family member, ApCPEB, is required for the persistence of activity-dependent increase in synaptic strength beyond 24 hours. In Drosophila, a CPEB family member Orb2 is required to stabilize memory beyond 12 hours. In mice and human a CPEB family member CPEB3 has been linked to episodic memory formation. These observations suggest that CPEB family members play evolutionarily conserved role in the persistence of memory. The Drosophila Orb2 gene produces two distinct primary transcripts from two different transcription start sites, encoding the Orb2A and Orb2B proteins. Mutations that selectively inactivate Orb2A protein specifically destabilize long-term memory. We have found that the Orb2A mRNA has two forms;an intron containing unspliced form that does not code for Orb2A protein (Orb2A-np) and a spliced form that codes for full length Orb2A protein (Orb2A-pc). Surprisingly, the Orb2A-np mRNA is the prevalent isoform in the adult brain and exposure to cues that form associative long-term memory in flies, such as exposure of hungry flies to sucrose and odor increases the level of protein coding spliced Orb2A-pc transcript. The Drosophila orthologue of mammalian splicing regulator Nova binds Orb2A transcript and regulates the formation of Orb2A-pc mRNA. In this proposal we intend to dissect the behavioral cues and Nova-dependent molecular mechanism that regulate the level of protein coding Orb2A transcript. We also intend to address when and how long Orb2 proteins are required for persistence of memory. We hope that an understanding of the interaction of experiences and molecules that stabilize memory would be useful to understand addictions and post traumatic syndromes, in which a single experience forms extremely stable memory. Also, we hope to gain insight into the role of regulated mRNA processing in long-lasting memory.
The proposed study intends to investigate when and how certain experience elicits stable memory. In this context we propose to study the role of Orb2-dependent protein synthesis and neuron-specific splicing regulator Nova-mediated mRNA processing in persistence of memory. These studies should provide general insights into the molecular basis of long-lasting memory.