Résumé :
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Spinal muscular atrophy is a recessive disease caused by mutations in the SMN1 gene, which encodes a protein (SMN) involved in RNA processing whose absence dramatically affects the survival of motor neurons. In Man, the severity of the disease is alleviated relatively to the SMN2 gene copy number, which varies from individual to individual.SMN2 differs from SMN1 by 5 nucleotides. Only one concerns the coding sequence: it is a silent C2T transition located at nucleotide +6 in exon 7. Accordingly, SMN2 encodes the same SMN protein as SMN1. However, the C2T transition affects the definition of exon 7 making that about 90% of SMN2 mRNAs miss exon 7. Here, we show that SMN activity could be restored in SMA cells by using tricyclo-DNA (Tc-DNA) antisense oligonucleotides annealing either the exon 7 terminal stem loop (TSL) or the nearby intron 7 splice silencer (ISS) of the SMN2 pre-mRNA. RT-PCR showed that about 30% and 60% of SMN2 mRNAs were rescued after treatment with Tc-DNA analogues annealing the TSL and ISS, respectively. For Tc-DNA[ISS], SMN levels were close to normal accordingly to Western blot analysis. Finally, immuno-staining revealed that rescued SMN was properly located in nuclear gems.
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