ELAV-like proteins bind and stabilize C/EBP mRNA in the induction of long-term memory in Aplysia

Abstract

Long-term memory (LTM) formation is a critical survival process by which an animal retains information about prior experiences in order to guide future behavior. In the experimentally advantageous marine mollusk Aplysia, LTM for sensitization can be induced by the presentation of two aversive shocks to the animals tail. Each of these training trials recruits distinct growth factor signaling systems that promote LTM formation. Specifically, whereas intact TrkB signaling during Trial 1 promotes an initial and transient increase of the immediate early gene apc/ebp mRNA, a prolonged increase in apc/ebp gene expression required for LTM formation requires the addition of TGF{beta} signaling during Trial 2. Here we explored the molecular mechanisms by which Trial 2 achieves the essential prolonged gene expression of apc/ebp. We find that this prolonged gene expression is not dependent on de novo transcription, but that apc/ebp mRNA synthesized by Trial 1 is post-transcriptionally stabilized by interacting with the RNA-binding protein ApELAV. This interaction is promoted by p38 MAPK activation initiated by TGF{beta}. We further demonstrate that blocking the interaction of ApELAV with its target mRNA during Trial 2 blocks both the prolonged increase in apc/ebp gene expression and the behavioral induction of LTM. Collectively, our findings elucidate both when and how ELAV proteins are recruited for the stabilization of mRNA in LTM formation. Significance StatementIn the present paper we significantly extend the general field of molecular processing in LTM by describing a novel form of pre-translational processing required for LTM which relies on the stabilization of a newly synthesized mRNA by a unique class of RNA binding proteins (ELAVs). In the broad field of molecular mechanisms of transcription-dependent LTM, there are now compelling data showing that important processing can occur after transcription of a gene, but before translation of the message into protein. Although the potential importance of ELAV proteins in LTM formation has previously been reported, to date there has been no mechanistic insight into the specific actions of ELAV proteins in stabilization of mRNAs known to be critical for LTM. Our new findings thus complement and extend this literature by demonstrating when and how this post-transcriptional gene regulation is mediated in the induction of LTM.