Survival motor neuron 2 pre-mRNA exon 7 splice-regulatory region

The Survival motor neuron 2 (SMN2) pre-mRNA exon 7 splice-regulatory region is a complex set of cis-acting elements that govern the inclusion of exon 7 during the processing of SMN2 transcripts. In patients with Spinal Muscular Atrophy (SMA), the loss of the SMN1 gene leaves them dependent on the SMN2 gene, which predominantly produces a truncated, non-functional protein due to a critical C-to-T transition that promotes exon 7 skipping (Lefebvre et al., 1995; Lorson et al., 1999). This regulatory region contains both exonic and intronic elements, most notably the Intronic Splicing Silencer N1 (ISS-N1), which serves as a primary inhibitory checkpoint (Singh et al., 2006). Therapeutic intervention at this site aims to redirect splicing to include exon 7, thereby restoring the production of full-length, functional SMN protein. This is achieved through antisense oligonucleotides that sequester inhibitory sequences or small molecules that stabilize the splicing machinery at weak splice sites (Hua et al., 2011; Ratni et al., 2018). Successfully targeting this region has transformed the clinical landscape for SMA, providing the first disease-modifying treatments for this previously fatal neurodegenerative disorder. These therapies demonstrate the landmark potential of RNA-targeted approaches to correct genetic defects at the transcript level.

Other names

ISS-N1Intronic splicing silencer N1SMN2 exon 7 splicing regulatory elementSMN2 intron 7 splicing silencerSMN2 pre-mRNA exon 7 regulatory region

Drugs targeting this region function by modulating the alternative splicing of SMN2 pre-mRNA. Antisense oligonucleotides like nusinersen bind to the intronic splicing silencer N1 (ISS-N1) to prevent the binding of negative splicing factors such as hnRNP A1/A2 (Singh et al., 2006). Small molecules like risdiplam and branaplam stabilize the interaction between the U1 small nuclear ribonucleoprotein (snRNP) and the 5' splice site of exon 7, as well as the exonic splicing enhancer 2 (ESE2), to promote exon inclusion (Ratni et al., 2018; Sivaramakrishnan et al., 2017).