An intronic element contributes to splicing repression in spinal muscular atrophy.
The neurodegenerative disease spinal muscular atrophy is caused by mutation of the survival motor neuron 1 (SMN1) gene. SMN2 is a nearly identical copy of SMN1 that is unable to prevent disease, because most SMN2 transcripts lack exon 7 and thus produce a nonfunctional protein. A key cause of inefficient SMN2 exon 7 splicing is a single nucleotide difference between SMN1 and SMN2 within exon 7. We previously provided evidence that this base change suppresses exon 7 splicing by creating an inhibitory element, a heterogeneous nuclear ribonucleoprotein (hnRNP) A1-dependent exonic splicing silencer. We now find that another rare nucleotide difference between SMN1 and SMN2, in intron 7, potentially creates a second SMN2-specific hnRNP A1 binding site. Remarkably, this single base change does indeed create a high-affinity hnRNP A1 binding site, and base substitutions that disrupt it restore exon 7 inclusion in vivo and prevent hnRNP A1 binding in vitro. We propose that interactions between hnRNP A1 molecules bound to the exonic and intronic sites cooperate to exclude exon 7 and discuss the significance of this exclusion with respect to SMN expression and splicing control more generally.
Kashima
Tsuyoshi
T
Department of Biological Sciences, Columbia University, New York, NY 10027, USA.
Rao
Nishta
N
Manley
James L
JL
D017398:Alternative Splicing / Q000235:genetics*; D001665:Binding Sites / Q000235:genetics; D017362:Cyclic AMP Response Element-Binding Protein / Q000235:genetics*; D034441:Heterogeneous-Nuclear Ribonucleoproteins / Q000235:genetics / Q000378:metabolism*; D006801:Humans; D047468:Immunoprecipitation; D007438:Introns / Q000235:genetics*; D009134:Muscular Atrophy, Spinal / Q000235:genetics*; D009419:Nerve Tissue Proteins / Q000235:genetics*; D010957:Plasmids / Q000235:genetics; D016133:Polymerase Chain Reaction; D020641:Polymorphism, Single Nucleotide / Q000235:genetics; D016601:RNA-Binding Proteins / Q000235:genetics*; D055532:SMN Complex Proteins; D055533:Survival of Motor Neuron 1 Protein; D055540:Survival of Motor Neuron 2 Protein
D017362:Cyclic AMP Response Element-Binding Protein; D034441:Heterogeneous-Nuclear Ribonucleoproteins; 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