Reactive oxygen (RO) has been identified as an important effector in ageing and lifespan determination. The specific cell types, however, in which oxidative damage acts to limit lifespan of the whole organism have not been explicitly identified. The association between mutations in the gene encoding the oxygen radical metabolizing enzyme CuZn superoxide dismutase (SOD1) and loss of motorneurons in the brain and spinal cord that occurs in the life-shortening paralytic disease, Familial Amyotrophic Lateral Sclerosis (FALS; ref. 4), suggests that chronic and unrepaired oxidative damage occurring specifically in motor neurons could be a critical causative factor in ageing. To test this hypothesis, we generated transgenic Drosophila which express human SOD1 specifically in adult motorneurons. We show that overexpression of a single gene, SOD1, in a single cell type, the motorneuron, extends normal lifespan by up to 40% and rescues the lifespan of a short-lived Sod null mutant. Elevated resistance to oxidative stress suggests that the lifespan extension observed in these flies is due to enhanced RO metabolism. These results show that SOD activity in motorneurons is an important factor in ageing and lifespan determination in Drosophila.

No abstract

Aerobic organisms possess an array of enzymatic defense mechanisms against the toxic effects of active oxygen species. These include CuZn superoxide dismutase (CuZn SOD), catalase (CAT), and glutathione peroxidase (GPOX). Insects, however, lack an independent GPOX enzyme and instead rely on the activity of the more general detoxification enzyme, glutathione-S-transferase (GST), to carry out a peroxidase function. We report here the developmental profile of GST in Drosophila melanogaster and show that GST is induced by paraquat, a known free-radical generating agent. We also report that glutathione (GSH) depletion induced by administration of buthionine sulfoximine (BSO) selectively reduces the viability of mutants lacking CuZnSOD. By measuring GST specific activity in flies carrying deficiencies for the 87B region, we confirm an earlier report that this region contains active GST-encoding genes. Finally, through a biochemical analysis of representative alleles of known lethal complementation gene. The implications of these findings to the role of GSH and GST in D. melanogaster oxygen defense are discussed.

Cu-Zn superoxide dismutase (cSOD) is an enzyme of critical importance for the inactivation of superoxide radicals generated by cellular metabolic processes. A phenotypic syndrome has been characterized for homozygotes for a null mutation of the Drosophila cSOD gene, many features of which may be relevant to current studies of cSOD mutations in mammals. However, it was possible that some of the features of this syndrome were at least partially attributable to genetic background differences between control and mutant strains. The results reported in this paper document that the previously described features of the cSOD-null phenotype, namely (i) adult sensitivity to paraquat, (ii) male sterility, (iii) female semisterility, (iv) adult life-span reduction, (v) adult hyperoxia sensitivity, (vi) larval radiation sensitivity, and (vii) developmental sensitivity to glutathione depletion, are all rescued by a cSOD+ transgene in a controlled cSOD-null genetic background. This clearly confirms that the phenotype is largely attributable to the cSOD mutation per se. We describe two new features of the cSOD-null phenotype, namely (viii) adult sensitivity to glutathione depletion, and (ix) adult sensitivity to ionizing radiation, which are ameliorated by the cSOD+ transgene. The distinct sensitivity of cSOD-deficient individuals, and the uniform resistance of the cSOD+ control strains, clearly establish the requirement for cSOD in protection against intrinsic and applied oxygen stress and set the stage for tissue-specific expression studies with the goal of elucidating the critical target(s) of damage in cSOD-deficient animals.

Restoring the rainforests of the Big Scrub is a powerful restoration symbol for the regional communities of far north coast New South Wales, but it is only a partly realized aspiration. What progress has been made in 35 years and to what extent is the aspiration achievable?