Inhibition of CPEB3 ribozyme elevates CPEB3 protein expression and polyadenylation of its target mRNAs, and enhances object location memory

Abstract

A self-cleaving ribozyme that maps to an intron of the cytoplasmic polyadenylation element binding protein 3 (CPEB3) gene is thought to play a role in human episodic memory, but the underlying mechanisms mediating this effect are not known. We tested the activity of the murine sequence and found that the ribozymes self-scission half-life matches the time it takes an RNA polymerase to reach the immediate downstream exon, suggesting that the ribozyme-dependent intron cleavage is tuned to co-transcriptional splicing of the CPEB3 mRNA. Our studies also reveal that the murine ribozyme modulates maturation of its harboring mRNA in both cultured cortical neurons and the hippocampus: inhibition of the ribozyme using an antisense oligonucleotide leads to increased CPEB3 protein expression, which enhances polyadenylation and translation of localized plasticity-related target mRNAs, and subsequently strengthens hippocampal-dependent long-term memory. These findings reveal a previously unknown role for self-cleaving ribozyme activity in regulating experience-induced co-transcriptional and local translational processes required for learning and memory. Significance StatementCytoplasmic polyadenylation-induced translation is one of the key steps for regulating protein synthesis and neuroplasticity in the hippocampus. The CPEB3 ribozyme is a highly conserved mammalian self-cleaving catalytic RNA with unknown biological roles. In this study, we investigated how the intronic ribozyme affects the CPEB3 mRNA maturation and translation, and its subsequent effect on memory formation. Our findings show that the ribozyme activity is anti-correlated with CPEB3 mRNA splicing: inhibition of the ribozyme results in higher mRNA and protein levels, which contribute to long-term memory. Our studies offer new insights into the role of the CPEB3 ribozyme in neuronal translational control for the activity-dependent synaptic functions that underlie long-term memory and demonstrate a novel biological role for self-cleaving ribozymes.