title: Molecular dissection of ALS-associated toxicity of SOD1 in transgenic mice using an exon-fusion approach.
abstract: Mutations in Cu,Zn superoxide dismutase (SOD1) are associated with amyotrophic lateral sclerosis (ALS). Among more than 100 ALS-associated SOD1 mutations, premature termination codon (PTC) mutations exclusively occur in exon 5, the last exon of SOD1. The molecular basis of ALS-associated toxicity of the mutant SOD1 is not fully understood. Here, we show that nonsense-mediated mRNA decay (NMD) underlies clearance of mutant mRNA with a PTC in the non-terminal exons. To further define the crucial ALS-associated SOD1 fragments, we designed and tested an exon-fusion approach using an artificial transgene SOD1(T116X) that harbors a PTC in exon 4. We found that the SOD1(T116X) transgene with a fused exon could escape NMD in cellular models. We generated a transgenic mouse model that overexpresses SOD1(T116X). This mouse model developed ALS-like phenotype and pathology. Thus, our data have demonstrated that a 'mini-SOD1' of only 115 amino acids is sufficient to cause ALS. This is the smallest ALS-causing SOD1 molecule currently defined. This proof of principle result suggests that the exon-fusion approach may have potential not only to further define a shorter ALS-associated SOD1 fragment, thus providing a molecular target for designing rational therapy, but also to dissect toxicities of other proteins encoded by genes of multiple exons through a 'gain of function' mechanism.
authors.affiliation: Davee Department of Neurology and Clinical Neurosciences, Northwestern University Feinberg School of Medicine, Chicago, IL 60611, USA. h-deng@northwestern.edu
authors.forename: Han-Xiang
authors.initials: HX
authors.lastname: Deng
authors.forename: Deng
authors.initials: D
authors.lastname: Han-Xiang
authors.forename: Hujun
authors.initials: H
authors.lastname: Jiang
authors.forename: Jiang
authors.initials: J
authors.lastname: Hujun
authors.forename: Ronggen
authors.initials: R
authors.lastname: Fu
authors.forename: Fu
authors.initials: F
authors.lastname: Ronggen
authors.forename: Hong
authors.initials: H
authors.lastname: Zhai
authors.forename: Zhai
authors.initials: Z
authors.lastname: Hong
authors.forename: Yong
authors.initials: Y
authors.lastname: Shi
authors.forename: Shi
authors.initials: S
authors.lastname: Yong
authors.forename: Erdong
authors.initials: E
authors.lastname: Liu
authors.forename: Liu
authors.initials: L
authors.lastname: Erdong
authors.forename: Makito
authors.initials: M
authors.lastname: Hirano
authors.forename: Hirano
authors.initials: H
authors.lastname: Makito
authors.forename: Mauro C
authors.initials: MC
authors.lastname: Dal Canto
authors.forename: C Dal Canto
authors.initials: CD
authors.lastname: Mauro
authors.forename: Teepu
authors.initials: T
authors.lastname: Siddique
authors.forename: Siddique
authors.initials: S
authors.lastname: Teepu
mesh_terms: D000595:Amino Acid Sequence / Q000235:genetics; D000690:Amyotrophic Lateral Sclerosis / Q000201:enzymology* / Q000235:genetics* / Q000473:pathology; D000818:Animals; D019677:Artificial Gene Fusion / Q000379:methods*; D018389:Codon, Nonsense; D004252:DNA Mutational Analysis; D004195:Disease Models, Animal; D005091:Exons; D006801:Humans; D051379:Mice; D008822:Mice, Transgenic; D020871:RNA Stability; D012333:RNA, Messenger / Q000378:metabolism; D017384:Sequence Deletion; D013482:Superoxide Dismutase / Q000235:genetics* / Q000378:metabolism*; D000072105:Superoxide Dismutase-1
chemical_list: D018389:Codon, Nonsense; D012333:RNA, Messenger; C000606290:SOD1 protein, human; C000606291:Sod1 protein, mouse; D013482:Superoxide Dismutase; D000072105:Superoxide Dismutase-1