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 alpha 1 with and without the gamma region at exon 10, are mainly produced in immature P19 cells. Remarkably, Mef2c isoforms containing exon beta specifically appeared in the neural cell stage. Because most transcripts contain exon beta in the neural cell stage and in the brain, this suggests that the alternative splicing of exon beta is highly regulated. Among known regulators, Fox-1 was specifically expressed in the neural cell stage in correlation with Mef2c exon beta. Fox-1 promoted exon beta inclusion in transfection experiments using Mef2c beta minigene. Moreover, we found that the promotion required RNA-binding activity of Fox-1 and GCAUG sequence located in adjacent intron of exon beta. Taken together, our results suggest that Fox-1, expressed specifically in the neural cell stage, promoted Mef2c exon beta inclusion via the GCAUG.