title: A negative element in SMN2 exon 7 inhibits splicing in spinal muscular atrophy.
abstract: Spinal muscular atrophy (SMA) is a relatively common neurodegenerative disease caused by homozygous loss of the survival motor neuron 1 (SMN1) gene. Humans possess a linked, nearly identical gene, SMN2, which produces a functional SMN protein but at levels insufficient to compensate for loss of SMN1 (refs. 1,2). A C/T transition at position +6 in exon 7 is all that differentiates the two genes, but this is sufficient to prevent efficient exon 7 splicing in SMN2 (refs. 2,3). Here we show that the C/T transition functions not to disrupt an exonic splicing enhancer (ESE) in SMN1 (ref. 4), as previously suggested, but rather to create an exonic splicing silencer (ESS) in SMN2. We show that this ESS functions as a binding site for a known repressor protein, hnRNP A1, which binds to SMN2 but not SMN1 exon 7 RNA. We establish the physiological importance of these results by using small interfering RNAs to reduce hnRNP A protein levels in living cells and show that this results in efficient SMN2 exon 7 splicing. Our findings not only define a new mechanism underlying the inefficient splicing of SMN2 exon 7 but also illustrate more generally the remarkable sensitivity and precision that characterizes control of mRNA splicing.
authors.affiliation: Department of Biological Sciences, Columbia University, New York, New York 10027, USA.
authors.forename: Tsuyoshi
authors.initials: T
authors.lastname: Kashima
authors.forename: James L
authors.initials: JL
authors.lastname: Manley
mesh_terms: D001483:Base Sequence; D017362:Cyclic AMP Response Element-Binding Protein; D004742:Enhancer Elements, Genetic; D005091:Exons; D006367:HeLa Cells; D000076245:Heterogeneous Nuclear Ribonucleoprotein A1; D034481:Heterogeneous-Nuclear Ribonucleoprotein Group A-B / Q000378:metabolism; D006801:Humans; D008957:Models, Genetic; D009134:Muscular Atrophy, Spinal / Q000235:genetics* / Q000378:metabolism; D009419:Nerve Tissue Proteins / Q000235:genetics*; D012313:RNA / Q000235:genetics / Q000378:metabolism; D034622:RNA Interference; D012326:RNA Splicing / Q000235:genetics*; D016601:RNA-Binding Proteins; D055532:SMN Complex Proteins; D037941:Silencer Elements, Transcriptional; D055533:Survival of Motor Neuron 1 Protein; D055540:Survival of Motor Neuron 2 Protein; D014162:Transfection
chemical_list: D017362:Cyclic AMP Response Element-Binding Protein; D000076245:Heterogeneous Nuclear Ribonucleoprotein A1; D034481:Heterogeneous-Nuclear Ribonucleoprotein Group A-B; 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; D012313:RNA