CPEB4 Knockout Mice Exhibit Normal Hippocampus-Related Synaptic Plasticity and Memory

Li-Yun Tsai,Yueh-Liang Tsou,Pei-Yi Lin,Wen-Hsuan Huang,Hsin-Jung Chou,Ta-Jen Liu,Ping-Tao Lee,Yu-Wei Chang,Yi-Shuian Huang,Michel Baudry

doi:10.1371/journal.pone.0084978

Abstract

Regulated RNA translation is critical to provide proteins needed to maintain persistent modification of synaptic strength, which underlies the molecular basis of long-term memory (LTM). Cytoplasmic polyadenylation element-binding proteins (CPEBs) are sequence-specific RNA-binding proteins and regulate translation in various tissues. All four CPEBs in vertebrates are expressed in the brain, including the hippocampal neurons, suggesting their potential roles in translation-dependent plasticity and memory. Although CPEB1 and CPEB3 have been shown to control specific kinds of hippocampus-related LTM, the role of CPEB2 and CPEB4 in learning and memory remains elusive. Thus, we generated CPEB4 knockout (KO) mice and analyzed them using several behavioral tests. No difference was found in the anxiety level, motor coordination, hippocampus-dependent learning and memory between the KO mice and their wild-type (WT) littermates. Electrophysiological recordings of multiple forms of synaptic plasticity in the Schaffer collateral pathway-CA1 neurons also showed normal responses in the KO hippocampal slices. Morphological analyses revealed that the CPEB4-lacking pyramidal neurons possessed slightly elongated dendritic spines. Unlike its related family members, CPEB1 and CPEB3, CPEB4 seems to be dispensable for hippocampus-dependent plasticity, learning and memory.

Highlights

The Cytoplasmic polyadenylation element-binding proteins (CPEBs) family of RNA-binding proteins in vertebrates contains CPEB1, CPEB2, CPEB3 and CPEB4, all of which are expressed in the brain [1] and share structure and sequence identity in the C-terminal RNA-binding domain (RBD) [2]
Using a radioactive probe against the exon 1 region, we found the presence of CPEB4 RNA in the KO brain (Figure 1C)
The reverse transcription-coupled Quantitative PCR (qPCR) (RTqPCR) assay with a set of primers spanning exon 7 and exon 8 region determined approximately 30% of CPEB4 RNA remained in the KO brain (Figure 1D), suggesting that the premature stop codon in the truncated CPEB4 transcript did not efficiently trigger non-sense-mediated RNA decay

Summary

Introduction

The CPEB family of RNA-binding proteins in vertebrates contains CPEB1, CPEB2, CPEB3 and CPEB4, all of which are expressed in the brain [1] and share structure and sequence identity in the C-terminal RNA-binding domain (RBD) [2]. Activation of N-methyl-D-aspartate (NMDA) receptors in neurons triggers calpain 2-mediated proteolysis of the repressor CPEB3, leading to translational upregulation of CPEB39s target RNAs in a polyadenylation-independent manner [2,11]. Monoubiquitination of CPEB3 by the E3 ligase, neuralized, converts CPEB3 from a repressor to an activator to promote polyadenylation-induced translation of GluA1 and GluA2 RNAs [12]. CPEB4 can promote polyadenylation and translation of RNAs required for second meiotic division in Xenopus oocytes and G2/M mitotic entry in HeLa cells [8,13]. To investigate whether the ablation of cpeb gene in vivo can recapitulate any defect identified previously using the knockdown approach or influence learning and memory, we generated the CPEB4 KO mice. Even though the dendritic spines of the KO neurons were slightly lengthened, this subtle disparity was not sufficient to cause obvious abnormalities in hippocampus-related plasticity and memory

Materials and Methods

Results

Discussion