An exonic enhancer is required for inclusion of an essential exon in the SMA-determining gene SMN.
The survival motor neuron genes, SMN1 and SMN2, encode identical proteins; however, only homo- zygous loss of SMN1 correlates with the development of spinal muscular atrophy (SMA). We have previously shown that a single non-polymorphic nucleotide difference in SMN exon 7 dramatically affects SMN mRNA processing. SMN1 primarily produces a full-length RNA whereas SMN2 expresses dramatically reduced full-length RNA and abundant levels of an aberrantly spliced transcript lacking exon 7. The importance of proper exon 7 processing has been underscored by the identification of several mutations within splice sites adjacent to exon 7. Here we show that an AG-rich exonic splice enhancer (ESE) in the center of SMN exon 7 is required for inclusion of exon 7. This region functioned as an ESE in a heterologous context, supporting efficient in vitro splicing of the Drosophila double-sex gene. Finally, the protein encoded by the exon-skipping event, Delta7, was less stable than full-length SMN, providing additional evidence of why SMN2 fails to compensate for the loss of SMN1 and leads to the development of SMA.
Lorson
C L
CL
Department of Dermatology, New England Medical Center and Tufts University School of Medicine, Boston, MA 02111, USA.
Androphy
E J
EJ
D017398:Alternative Splicing / Q000235:genetics; D001483:Base Sequence; D017362:Cyclic AMP Response Element-Binding Protein; D004742:Enhancer Elements, Genetic / Q000235:genetics*; D005091:Exons / Q000235:genetics*; D006801:Humans; D008969:Molecular Sequence Data; D009134:Muscular Atrophy, Spinal / Q000235:genetics*; D009419:Nerve Tissue Proteins / Q000235:genetics*; D016601:RNA-Binding Proteins; D055532:SMN Complex Proteins; D055533:Survival of Motor Neuron 1 Protein; D055540:Survival of Motor Neuron 2 Protein; 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; D055533:Survival of Motor Neuron 1 Protein; D055540:Survival of Motor Neuron 2 Protein