Drosophila Orb2 targets genes involved in neuronal growth, synapse formation, and protein turnover

Abstract

In the study of long-term memory, how memory persists is a fundamental and unresolved question. What are the molecular components of the long-lasting memory trace? Previous studies in Aplysia and Drosophila have found that a neuronal variant of a RNA-binding protein with a self-perpetuating prion-like property, cytoplasmic polyadenylation element binding protein, is required for the persistence of long-term synaptic facilitation in the snail and long-term memory in the fly. In this study, we have identified the mRNA targets of the Drosophila neuronal cytoplasmic polyadenylation element binding protein, Orb2. These Orb2 targets include genes involved in neuronal growth, synapse formation, and intriguingly, protein turnover. These targets suggest that the persistent form of the memory trace might be comprised of molecules that maintain a sustained, permissive environment for synaptic growth in an activated synapse.protein synthesis | synaptic plasticity | memory

RNA-binding profiles of Drosophila CPEB proteins Orb and Orb2

“…As expected from previous studies, the binding sites of Drosophila CPEB proteins (26,27) are located preferentially in 3′ UTR regions: 22.5% of all Orb2-bound and 37% of all Orbbound reads are located in 3′ UTR regions, although this genomic feature only covers 3.4% of the fly genome (6.6× and 10.8× enrichment, respectively) ( Fig. 2A).…”

“…Other reports suggest that both CPEB1 and CPEB4 recognize and control at least partially overlapping sets of mRNA targets and bind the same motif (23)(24)(25). Although a small number of fly Orb2 mRNA targets was described (26), the authors could not identify the bound sequence unambiguously. Thus, the full spectrum of fly CPEB targets is largely unknown, with previous studies characterizing only a limited number of interacting mRNAs (26)(27)(28).…”

“…Orb2 mRNA is expressed endogenously in S2 cells [average reads per kilobase of transcript per million reads mapped (RPKM) = 8.5; n = 2], and more than 90% of their transcriptome is detectable (RPKM >1) in the neuronal and gonad tissues, which express CPEB proteins in vivo (SI Analysis) (31). This expression and the fact that S2 cells allow Orb2-mediated translational suppression (26) suggest that S2 cells constitute a suitable system for investigating the transcriptomewide Orb2-binding profile. Importantly, in S2 cells the overexpressed Orb2A exists in the form of protein clusters, reflecting its endogenous propensity to aggregate (Fig.…”

“…Although a small number of fly Orb2 mRNA targets was described (26), the authors could not identify the bound sequence unambiguously. Thus, the full spectrum of fly CPEB targets is largely unknown, with previous studies characterizing only a limited number of interacting mRNAs (26)(27)(28). Elucidation of the RNA-binding specificity of Orb2 and the identification of its mRNA targets is essential to understand the role of downstream effectors in local translation-dependent processes, including LTM formation.…”

Long-term memory consolidation: The role of RNA-binding proteins with prion-like domains

“…The translation of target mRNAs is suppressed when either of the 2 isoforms are expressed in S2 cells that lack endogenous Orb2, clearly indicating a role for Orb2 in mRNA repression. 149 Taken together, the results indicate that Orb2 is required for the maintenance of long-term memory through a mechanism that requires its N-terminal domain as well as its ability to regulate translation of mRNAs required for stable alteration of activated synapses.…”