Long-term memory (LTM) formation is a critical survival process by which an animal retains information about prior experiences 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 animal's 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 TGFβ 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 TGFβ. 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. Stabilization of a transiently expressed immediate early gene mRNA by a repeated training trial may therefore serve as a "filter" for learning, permitting only specific events to cause lasting transcriptional changes and behavioral LTM.

SIGNIFICANCE STATEMENT: In the present paper, we significantly extend the general field of molecular processing in long-term memory (LTM) by describing a novel form of pretranslational processing required for LTM, which relies on the stabilization of a newly synthesized mRNA by a class of RNA binding proteins (ELAVs). 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, the specific actions of ELAV proteins during LTM formation remained to be understood. 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.

长期记忆 (LTM) 形成是一个关键的生存过程，动物通过该过程保留有关先前经历的信息以指导未来的行为。在实验上有利的海洋软体动物Aplysia 中，可以通过对动物尾部进行两次厌恶性电击来诱导 LTM 致敏。这些训练试验中的每一个都招募了促进 LTM 形成的不同生长因子信号系统。具体而言，而试验1期间完好TrkB信号促进立即早期基因的初始和瞬时增加APC / EBP的mRNA，在延长的增加APC / EBPLTM 形成所需的基因表达需要在试验 2 期间添加 TGFβ 信号传导。在这里我们探讨了试验 2 实现apc/ebp基本延长基因表达的分子机制。我们发现这种延长的基因表达不依赖于从头转录，但试验 1 合成的apc/ebp mRNA 通过与 RNA 结合蛋白 ApELAV 相互作用而在转录后稳定。这种相互作用是由 TGFβ 启动的 p38 MAPK 激活促进的。我们进一步证明，在试验 2 期间阻断 ApELAV 与其靶 mRNA 的相互作用可以阻断apc/ebp的延长增加LTM 的基因表达和行为诱导。总的来说，我们的研究结果阐明了何时以及如何招募 ELAV 蛋白以稳定 LTM 形成中的 mRNA。因此，通过重复训练试验稳定瞬时表达的即时早期基因 mRNA 可以作为学习的“过滤器”，仅允许特定事件引起持久的转录变化和行为 LTM。

意义陈述：在本文中，我们通过描述 LTM 所需的一种新的翻译前处理形式，显着扩展了长期记忆 (LTM) 中分子处理的一般领域，该形式依赖于新合成的 mRNA 的稳定性。 RNA 结合蛋白 (ELAV)。现在有令人信服的数据表明，重要的加工可以发生在基因转录之后，但在信息翻译成蛋白质之前。尽管之前已经报道了 ELAV 蛋白在 LTM 形成中的潜在重要性，但 ELAV 蛋白在 LTM 形成过程中的具体作用仍有待了解。因此，我们的新发现通过证明在 LTM 的诱导中何时以及如何介导这种转录后基因调控来补充和扩展该文献。