Molecular dissection of ALS-associated toxicity of SOD1 in transgenic mice using an exon-fusion approach.
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.
Deng
Han-Xiang
HX
Davee Department of Neurology and Clinical Neurosciences, Northwestern University Feinberg School of Medicine, Chicago, IL 60611, USA. h-deng@northwestern.edu
Han-Xiang
Deng
D
Jiang
Hujun
H
Hujun
Jiang
J
Fu
Ronggen
R
Ronggen
Fu
F
Zhai
Hong
H
Hong
Zhai
Z
Shi
Yong
Y
Yong
Shi
S
Liu
Erdong
E
Erdong
Liu
L
Hirano
Makito
M
Makito
Hirano
H
Dal Canto
Mauro C
MC
Mauro
C Dal Canto
CD
Siddique
Teepu
T
Teepu
Siddique
S
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
D018389:Codon, Nonsense; D012333:RNA, Messenger; C000606290:SOD1 protein, human; C000606291:Sod1 protein, mouse; D013482:Superoxide Dismutase; D000072105:Superoxide Dismutase-1