Regulation of murine survival motor neuron (Smn) protein levels by modifying Smn exon 7 splicing.
Proximal spinal muscular atrophy (SMA) is caused by mutations in the survival motor neuron gene (SMN1). In humans, two nearly identical copies of SMN exist and differ only by a single non-polymorphic C-->T nucleotide transition in exon 7. SMN1 contains a 'C' nucleotide at the +6 position of exon 7 and produces primarily full-length SMN transcripts, whereas SMN2 contains a 'T' nucleotide and produces high levels of a transcript that lacks exon 7 and a low level of full-length SMN transcripts. All SMA patients lack a functional SMN1 gene but retain at least one copy of SMN2, suggesting that the low level of full-length protein produced from SMN2 is sufficient for all cell types except motor neurons. The murine Smn gene is not duplicated or alternatively spliced. It resembles SMN1 in that the critical exon 7 +6 'C' nucleotide is conserved. We have generated Smn minigenes containing either wild-type Smn exon 7 or an altered exon 7 containing the C-->T nucleotide transition to mimic SMN2. When expressed in cultured cells or transgenic mice, the wild-type minigene produced only full-length transcripts whereas the modified minigene alternatively spliced exon 7. Furthermore, Smn exon 7 contains a critical AG-rich exonic splice enhancer sequence (ESE) analogous to the human ESE within SMN exon 7, and subtle mutations within the mESE caused a variation in Smn transcript levels. In summary, we show for the first time that the murine Smn locus can be induced to alternatively splice exon 7. These results demonstrate that SMN protein levels can be varied in the mouse by the introduction of specific mutations at the endogenous Smn locus and thereby lay the foundation for developing animals that closely 'resemble' SMA patients.
DiDonato
C J
CJ
Ottawa Health Research Institute and The University of Ottawa Center for Neuromuscular Disease, Ottawa, Ontario K1H 8L6, Canada.
Lorson
C L
CL
De Repentigny
Y
Y
Simard
L
L
Chartrand
C
C
Androphy
E J
EJ
Kothary
R
R
D017398:Alternative Splicing; D000818:Animals; D001482:Base Composition / Q000235:genetics; D001483:Base Sequence; D019556:COS Cells; D002460:Cell Line; D017362:Cyclic AMP Response Element-Binding Protein; D004742:Enhancer Elements, Genetic / Q000235:genetics; D005091:Exons / Q000235:genetics*; D005786:Gene Expression Regulation; D006367:HeLa Cells; D006801:Humans; D051379:Mice; D008822:Mice, Transgenic; D008969:Molecular Sequence Data; D009154:Mutation; D009419:Nerve Tissue Proteins / Q000235:genetics* / Q000378:metabolism; D010957:Plasmids / Q000235:genetics; D012313:RNA / Q000235:genetics / Q000378:metabolism; D016601:RNA-Binding Proteins; D020133:Reverse Transcriptase Polymerase Chain Reaction; D055532:SMN Complex Proteins; D012689:Sequence Homology, Nucleic Acid; D055533:Survival of Motor Neuron 1 Protein; D055540:Survival of Motor Neuron 2 Protein; D014018:Tissue Distribution; D014158:Transcription, Genetic; D014407:Tumor Cells, Cultured
D017362:Cyclic AMP Response Element-Binding Protein; D009419:Nerve Tissue Proteins; D016601:RNA-Binding Proteins; D055532:SMN Complex Proteins; C526471:SMN1 protein, human; C526477:SMN2 protein, human; C526472:Smn1 protein, mouse; D055533:Survival of Motor Neuron 1 Protein; D055540:Survival of Motor Neuron 2 Protein; D012313:RNA