Loss of CaV1.3 RNA editing enhances mouse hippocampal plasticity, learning, and memory.

L-type CaV1.3 calcium channels are expressed on the dendrites and soma of neurons, and there is a paucity of information about its role in hippocampal plasticity. Here, by genetic targeting to ablate CaV1.3 RNA editing, we demonstrate that unedited CaV1.3ΔECS mice exhibited improved learning and enhanced long-term memory, supporting a functional role of RNA editing in behavior. Significantly, the editing paradox that functional recoding of CaV1.3 RNA editing sites slows Ca2+-dependent inactivation to increase Ca2+ influx but reduces channel open probability to decrease Ca2+ influx was resolved. Mechanistically, using hippocampal slice recordings, we provide evidence that unedited CaV1.3 channels permitted larger Ca2+ influx into the hippocampal pyramidal neurons to bolster neuronal excitability, synaptic transmission, late long-term potentiation, and increased dendritic arborization. Of note, RNA editing of the CaV1.3 IQ-domain was found to be evolutionarily conserved in mammals, which lends support to the importance of the functional recoding of the CaV1.3 channel in brain function.

Tissue-selective restriction of RNA editing of CaV1.3 by splicing factor SRSF9.

Adenosine DeAminases acting on RNA (ADAR) catalyzes adenosine-to-inosine (A-to-I) conversion within RNA duplex structures. While A-to-I editing is often dynamically regulated in a spatial-temporal manner, the mechanisms underlying its tissue-selective restriction remain elusive. We have previously reported that transcripts of voltage-gated calcium channel CaV1.3 are subject to brain-selective A-to-I RNA editing by ADAR2. Here, we show that editing of CaV1.3 mRNA is dependent on a 40 bp RNA duplex formed between exon 41 and an evolutionarily conserved editing site complementary sequence (ECS) located within the preceding intron. Heterologous expression of a mouse minigene that contained the ECS, intermediate intronic sequence and exon 41 with ADAR2 yielded robust editing. Interestingly, editing of CaV1.3 was potently inhibited by serine/arginine-rich splicing factor 9 (SRSF9). Mechanistically, the inhibitory effect of SRSF9 required direct RNA interaction. Selective down-regulation of SRSF9 in neurons provides a basis for the neuron-specific editing of CaV1.3 transcripts.

RNA editing of ion channels and receptors in physiology and neurological disorders.

Adenosine-to-inosine (A-to-I) RNA editing is a post-transcriptional modification that diversifies protein functions by recoding RNA or alters protein quantity by regulating mRNA level. A-to-I editing is catalyzed by adenosine deaminases that act on RNA. Millions of editing sites have been reported, but they are mostly found in non-coding sequences. However, there are also several recoding editing sites in transcripts coding for ion channels or transporters that have been shown to play important roles in physiology and changes in editing level are associated with neurological diseases. These editing sites are not only found to be evolutionary conserved across species, but they are also dynamically regulated spatially, developmentally and by environmental factors. In this review, we discuss the current knowledge of A-to-I RNA editing of ion channels and receptors in the context of their roles in physiology and pathological disease. We also discuss the regulation of editing events and site-directed RNA editing approaches for functional study that offer a therapeutic pathway for clinical applications.