Intronic < i > PAH < /i > gene mutations cause a splicing defect by a novel mechanism involving U1snRNP binding downstream of the 5 ’ splice site

In this study, we report a novel intron 11 regulatory element, which is involved in exon 11 splicing, as revealed by the investigated pathogenic effect of variants c .1199+17G>A and c.1199+20G>C, identified in PKU patients. Both mutations cause exon 11 skipping in a minigene system. RNA binding assays indicate that binding of U1snRNP70 to this intronic region is disrupted, concomitant with a slightly increased binding of inhibitors hnRNPA1/2. We have investigated the effect of deletions and point mutations, as well as overexpression of adapted U1snRNA to show that this splicing regulatory motif is important for regulation of correct splicing at the natural 5 ’ splice site. The results indicate that U1snRNP binding downstream of the natural 5’ splice site determines efficient exon 11 splicing, thus providing a basis for development of therapeutic strategies to correctPAH exon 11 splicing mutations. In this work, we expand the functional effects of non-canonical intronic U1 snRNP binding by showing that it may enhance exon definition and that, consequently, intronic mutations may cause exon skipping by a novel mechanism, where they disrupt stimulatory U1 snRNP binding close to the 5 ’ splice site. Notably, our results provide further understanding of the reported therapeutic effect of exon specific U1 snRNA for splicing mutations in disease.
Source: PLoS Genetics - Category: Genetics & Stem Cells Authors: Source Type: research