Activation of a cryptic 5′ splice site reverses the impact of pathogenic splice site mutations in the spinal muscular atrophy gene
Del Rio-Malewski, Jose Bruno
Spinal muscular atrophy (SMA) is caused by deletions or mutations of the Survival Motor Neuron 1 (SMN1) gene coupled with predominant skipping of SMN2 exon 7. The only approved SMA treatment is an antisense oligonucleotide that targets the intronic splicing silencer N1 (ISS-N1), located downstream of the 5′ splice site (5′ss) of exon 7. Here, we describe a novel approach to exon 7 splicing modulation through activation of a cryptic 5′ss (Cr1). We discovered the activation of Cr1 in transcripts derived from SMN1 that carries a pathogenic G-to-C mutation at the first position (G1C) of intron 7. We show that Cr1-activating engineered U1 snRNAs (eU1s) have the unique ability to reprogram pre-mRNA splicing and restore exon 7 inclusion in SMN1 carrying a broad spectrum of pathogenic mutations at both the 3′ss and 5′ss of the exon 7. Employing a splicing-coupled translation reporter, we demonstrate that mRNAs generated by an eU1-induced activation of Cr1 produce full-length SMN. Our findings underscore a wider role for U1 snRNP in splicing regulation and reveal a novel approach for the restoration of SMN exon 7 inclusion for a potential therapy of SMA.
This article is published as Singh, Natalia N., José Bruno Del Rio-Malewski, Diou Luo, Eric W. Ottesen, Matthew D. Howell, and Ravindra N. Singh. "Activation of a cryptic 5′ splice site reverses the impact of pathogenic splice site mutations in the spinal muscular atrophy gene." Nucleic acids research 45, no. 21 (2017): 12214-12240. doi: 10.1093/nar/gkx824. Posted with permission.