Sr. Lim et Kj. Hertel, Modulation of survival motor neuron pre-mRNA splicing by inhibition of alternative 3 ' splice site pairing, J BIOL CHEM, 276(48), 2001, pp. 45476-45483
Spinal muscular atrophy is caused by the loss of functional survival motor
neuron (SMN1) alleles. A translationally silent nucleotide transition in th
e duplicated copy of the gene (SMN2) leads to exon 7 skipping and expressio
n of a nonfunctional gene product. It has been suggested that differential
SMN2 splicing is caused by the disruption of an exonic splicing enhancer. H
ere we show that the single nucleotide difference reduces the intrinsic str
ength of the 3' splice site of exon 7 2-fold, whereas the strength of the 5
' splice site of the exon 7 is not affected. Thus, a decrease in splice sit
e strength is magnified in the context of competing exons. These data sugge
st that lower levels of exon 7 definition not only reduce intron 6 removal
but, more importantly, increase the efficiency of the competing exon 7 skip
ping pathway. Antisense oligonucleotides were tested to modulate exon 7 inc
lusion, which contains the authentic translation stop codon. Oligonucleotid
es directed toward the 3' splice site of exon 8 were shown to alter SMN2 sp
licing in favor of exon 7 inclusion. These results suggest that antisense o
ligonucleotides could be used as a therapeutic strategy to counteract the p
rogression of SMA.