New protein synthesis is known to be required for the consolidation of memories, yet existing methods to block translation lack spatiotemporal precision and cell-type specificity, preventing investigation of cell-specific contributions of protein synthesis. Here, we developed a combined knock-in mouse and chemogenetic approach for cell type-specific and drug-inducible protein synthesis inhibition (ciPSI) that enables rapid and reversible phosphorylation of eIF2α, leading to inhibition of general translation by 50% in vivo. We use ciPSI to show that targeted protein synthesis inhibition pan-neuronally and in excitatory neurons in lateral amygdala (LA) impaired long-term memory. This could be recovered with artificial chemogenetic activation of LA neurons, though at the cost of stimulus generalization. Conversely, genetically reducing phosphorylation of eIF2α in excitatory neurons in LA enhanced memory strength, but reduced memory fidelity and behavioral flexibility. Our findings provide evidence for a cell-specific translation program during consolidation of threat memories. Users may view, print, copy, and download text and data-mine the content in such documents, for the purposes of academic research, subject always to the full Conditions of use:

To survive in a dynamic environment, animals need to identify and appropriately respond to stimuli that signal danger 1 . Survival also depends on suppressing the threat-response during a stimulus that predicts absence of threat, i.e. safety 2 – 5 . Understanding the biological substrates of emotional memories in which animals learn to flexibly execute defensive responses to a threat-predictive cue and a safety cue is critical for developing treatments for memory disorders such as PTSD 5 . A key brain area for processing and storing threat memories is the centrolateral amygdala (CeL), which is an important node in the neuronal circuit mediating defensive responses 6 – 9 . Here, we applied intersectional chemogenetic strategies in CeL inhibitory neurons (INs) to block cell-type-specific translation programs that are sensitive to depletion of eukaryotic initiation factor 4E (eIF4E) and phosphorylation of eukaryotic initiation factor 2α (p-eIF2α), respectively. We show that de novo translation in CeL Somatostatin-expressing (SOM) INs is necessary for long-term storage of conditioned-threat response whereas de novo translation in CeL protein kinase Cδ (PKCδ)-expressing INs is necessary for conditioned-response inhibition to a safety cue. Our results provide new insight into the role of de novo protein synthesis in distinct CeL inhibitory neuron populations during consolidation of long-term memories.

Malignant tumors of the central nervous system (CNS) are the 10th most frequent cause of cancer mortality. Despite the strong malignancy of some such tumors, oncogenic mutations are rarely found in classic members of the RAS family of small GTPases. This raises the question as to whether other RAS family members may be affected in CNS tumors, excessively activating RAS pathways. The RAS-related subfamily of GTPases is that which is most closely related to classical Ras and it currently contains 3 members: RRAS, RRAS2 and RRAS3. While R-RAS and R-RAS2 are expressed ubiquitously, R-RAS3 expression is restricted to the CNS. Significantly, both wild type and mutated RRAS2 (also known as TC21) are overexpressed in human carcinomas of the oral cavity, esophagus, stomach, skin and breast, as well as in lymphomas. Hence, we analyzed the expression of R-RAS2 mRNA and protein in a wide variety of human CNS tumors and we found the R-RAS2 protein to be overexpressed in all of the 90 CNS cancer samples studied, including glioblastomas, astrocytomas and oligodendrogliomas. However, R-Ras2 was more strongly expressed in low grade (World Health Organization grades I-II) rather than high grade (grades III-IV) tumors, suggesting that R-RAS2 is overexpressed in the early stages of malignancy. Indeed, R-RAS2 overexpression was evident in pre-malignant hyperplasias, both at the mRNA and protein levels. Nevertheless, such dramatic changes in expression were not evident for the other two subfamily members, which implies that RRAS2 is the main factor triggering neural transformation.

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