Figure 1.

Engineered U1 Was Able to Reduce Exon Skipping, But Failed to Prevent Intron Retention

Schematic drawings show parts of the pre-mRNA of exon 5-intron 5-exon 6 of BBS1 and summarize the observed splice variants of BBS1. The splice donor site is underlined. Capital letters denote exonic bases and small letters represent intronic bases. The BBS1 gene mutation c.479G > A (red letter) locates to the last base of exon 5 and causes both exon 5 skipping (220 bp) and intron 5 retention (373 bp) in BBS1 transcripts. Residual levels of correctly spliced BBS1 transcripts (267 bp) were detectable in untreated patient-derived fibroblast cells using RT-PCR analyses and agarose gel electrophoresis. U1 snRNA was engineered to show full complementarity to the mutated splice donor site in BBS1 (green drawing, complementary base pairs: GGUcacucu). Upon treatment of the patient-derived fibroblasts with the engineered U1, exon 5 skipping can be reverted and increased amounts of correctly spliced BBS1 transcripts were detected (green arrow). In contrast, the intron 5 retention remained unchanged by the U1 treatment. kb, kilo bases; bp, base pairs.