Alternative splicing of Mef2c promoted by Fox-1 during neural differentiation in P19 cells.

Mef2c protein is one of the MADS-box type transcription factors involved in muscular differentiation and synaptic formation. Previously, it has been reported that the Mef2c gene is responsible for three alternative splicing regulations. Here, we investigated the alternative splicing variants of Mef2c during neural differentiation of P19 cells and during cardio muscular differentiation of P19 clone 6 (P19CL6). We detected that two Mef2c mRNA isoforms, using exon α1 with and without the γ region at exon 10, are mainly produced in immature P19 cells. Remarkably, Mef2c isoforms containing exon ß specifically appeared in the neural cell stage. Because most transcripts contain exon ß in the neural cell stage and in the brain, this suggests that the alternative splicing of exon ß is highly regulated. Among known regulators, Fox-1 was specifically expressed in the neural cell stage in correlation with Mef2c exon ß. Fox-1 promoted exon ß inclusion in transfection experiments using Mef2cß minigene. Moreover, we found that the promotion required RNA-binding activity of Fox-1 and GCAUG sequence located in adjacent intron of exon ß. Taken together, our results suggest that Fox-1, expressed specifically in the neural cell stage, promoted Mef2c exon ß inclusion via the GCAUG.

Neuron-specific splicing.

During pre-mRNA splicing events, introns are removed from the pre-mRNA, and the remaining exons are connected together to form a single continuous molecule. Alternative splicing is a common mechanism for the regulation of gene expression in eukaryotes. More than 90% of human genes are known to undergo alternative splicing. The most common type of alternative splicing is exon skipping, which is also known as cassette exon. Other known alternative splicing events include alternative 5' splice sites, alternative 3' splice sites, intron retention, and mutually exclusive exons. Alternative splicing events are controlled by regulatory proteins responsible for both positive and negative regulation. In this review, we focus on neuronal splicing regulators and discuss several notable regulators in depth. In addition, we have also included an example of splicing regulation mediated by the RBFox protein family. Lastly, as previous studies have shown that a number of splicing factors are associated with neuronal diseases such as Alzheime's disease (AD) and Autism spectrum disorder (ASD), here we consider their importance in neuronal diseases wherein the underlying mechanisms have yet to be elucidated.