Correction of SMN2 Pre-mRNA splicing by antisense U7 small nuclear RNAs

Mutations in one of the duplicated survival of motor neuron (SMN) genes lead to the progressive loss of motor neurons and subsequent development of spinal muscular atrophy (SMA), a common, and usually fatal, hereditary disease. Homozygous absence of the telomeric copy (SMN1) correlates with development of SMA because differential splicing of the centromeric copy (SMN2) leads to exon 7 skipping and predominantly produces a biologically inactive protein isoform. To increase exon 7 inclusion of SMN2, we have designed a series of vectors that express modified U7 snRNAs containing antisense sequences complementary to the 3' splice site of SMN exon 8. Over 20 anti-SMN U7 snRNAs were tested for their ability to promote exon 7 inclusion in the SMN2 gene. Transient expression of anti-SMN U7 snRNAs in HeLa cells modulated SMN2 splicing to approximately 70% exon 7 inclusion in a sequence-specific and dose-dependent manner. Significantly, the administration of anti-SMN U7 snRNPs results in an increase in the concentration of SMN protein. These results suggest that modulation of SMN2 pre-mRNA splicing by modified U7 snRNAs provides a promising form of gene therapy for the treatment of SMA.