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Amyotrophic lateral sclerosis is neurodegenerative disease characterized by late-onset, loss of motor neurons, paralysis, and eventual death. SOD1 is a free radical scavenger that normally resides in the cytoplasm, nucleus, and intermembrane space of the mitochondria. Mutations in SOD1, a ubiquitously expressed free-radical scavenger, are one cause of ALS. Degeneration of motor neurons is thought to be triggered by aggregation of mutant SOD1 followed by propagation to adjacent cells though cell-cell contacts. Here, we present immunohistochemical findings on tissues of a Drosophila melanogaster expressing mutant dsod1 alleles at the endogenous locus. Aggregate-specific antibodies were used to assess the presence of aggregates in salivary gland tissues and the CNS for mutant and wildtype sod1 alleles. Immunocytochemistry revealed the presence of large cytoplasmic aggregates near the nuclei of larval salivary glands of dsod1G85R/G85R mutants and in the salivary glands and CNS of dsod1H48R/H48R mutants. Aggregation phenotypes occurred with partial penetrance and penetrance did not increase with age. Furthermore, because both dsod1G85R/G85R and dsod1H48R/H48R mutants exhibit lethal phenotypes with complete penetrance, our data suggest a lack of correlation between the presence of visible aggregates and toxicity.

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