Fig. 5

Mechanisms of action of splice-switching antisense oligonucleotides. a Stimulating splicing factors (SF) shown in pink circles such as SR proteins binding to exon splicing enhancers (ESE) promote the inclusion of an exon, while inhibitory SF in green circles such as hnRNPs binding to intron splicing silencers (ISS) inhibit exon inclusion. When promoting outweighs inhibiting actions, exons are included to generate a full-length transcript and wild-type protein. b Antisense oligomers (AOs) annealing to ESE blocks the interaction between SF and ESE and induces targeted (i) in-frame exon skipping, thus inducing in-frame transcripts and correspondingly new protein isoforms; and (ii) out-of-frame exon skipping and disrupts the reading frame and creates premature stop codon (PTC) in a downstream exon, that may lead to nonsense-mediated mRNA decay of the targeted transcript and downregulation of the protein. (iii) AOs anneal to ISS to increase targeted exon inclusion and generate a full-length transcript and wild-type protein.