Abstract
Alternative splicing is a finely regulated mechanism in eukaryotes that allows increasing the complexity of the proteome and diversifying cellular functions. In human genes, recognition of authentic splice sites by the spliceosome is challenged by the high number of exons and the presence of large introns as observed in the 2.2 megabase long DMD gene containing 79 exons. In addition to the already known cis sequences and trans factors, it has been reported that the exon junction complex (EJC) contributes to the maintenance of transcriptome integrity. The deposition of the complex composed of four core proteins (eIF4A3, Y14, Magoh and MLN51) 24 nucleotides upstream of each exon-exon junction represses the occurrence of spurious re-splicing events. During my thesis, I studied the role of EJC in the splicing of the muscle isoform (Dp427m) of the DMD gene which includes all 79 exons and of the ubiquitous isoform (Dp71) characterized by multiple alternative splicing in the brain, using RNAi and targeted RNA-Seq approaches in human cell lines. We have shown that decreasing the expression level of EJC factors deregulates the splicing of exons 68 to 78 in the 3' region of the transcripts in a similar manner in both isoforms and that the associated ASAP/PSAP complexes are also involved in the control of the splicing of exons 71 and 78, whose inclusion level is highly regulated according to tissue and/or developmental stage. We also observed that decreased expression of eIF4A3 prevents the initiation of myoblast differentiation into myotubes. Thus, our data show that the EJC contributes to the fidelity of splicing of exons encoding the C-terminal domain of dystrophin, a protein-protein interaction domain essential for the structural and signaling functions of dystrophin, and also plays a role in myogenic differentiation.