Expression of bovine superoxide dismutase in Drosophila melanogaster augments resistance of oxidative stress

Oxidative stress and visual system: a review

Different types of tissues respond differently to the action of oxidative stress. The visual system is very sensitive to oxidative action due to continuous exposure to light. In consideration of the growing interest of scientific studies towards various compounds endowed with antioxidant and anti-inflammatory properties, we performed a review of the literature focusing on the use of some antioxidant molecules for the treatment of conditions affecting the visual system. In this study, we focused on the ability of two antioxidant agents, the small molecule α-lipoic acid (ALA) and the enzyme superoxide dismutase (SOD), to influence the neurodegenerative physiological processes related to aging and oxidative stress affecting the ocular segment. The literature data report that ALA and SOD can protect against neurodegenerative effects both the optic nerve and retina and, if administered together, they are able to lower the levels of oxidative stress, thus preventing neurodegeneration and reducing the apoptotic process.

Amyotrophic Lateral Sclerosis Genes in Drosophila melanogaster

Amyotrophic lateral sclerosis (ALS) is a devastating adult-onset neurodegenerative disease characterized by the progressive degeneration of upper and lower motoneurons. Most ALS cases are sporadic but approximately 10% of ALS cases are due to inherited mutations in identified genes. ALS-causing mutations were identified in over 30 genes with superoxide dismutase-1 (SOD1), chromosome 9 open reading frame 72 (C9orf72), fused in sarcoma (FUS), and TAR DNA-binding protein (TARDBP, encoding TDP-43) being the most frequent. In the last few decades, Drosophila melanogaster emerged as a versatile model for studying neurodegenerative diseases, including ALS. In this review, we describe the different Drosophila ALS models that have been successfully used to decipher the cellular and molecular pathways associated with SOD1, C9orf72, FUS, and TDP-43. The study of the known fruit fly orthologs of these ALS-related genes yielded significant insights into cellular mechanisms and physiological functions. Moreover, genetic screening in tissue-specific gain-of-function mutants that mimic ALS-associated phenotypes identified disease-modifying genes. Here, we propose a comprehensive review on the Drosophila research focused on four ALS-linked genes that has revealed novel pathogenic mechanisms and identified potential therapeutic targets for future therapy.

Biomolecular Modulation of Neurodegenerative Events during Ageing

The objective is to assess the modulation of retinal and optic nerve degenerative events induced by the combination of α-lipoic acid (ALA) and superoxide dismutase (SOD) in an animal model of ageing. For this study, 24 male Wistar-Harlan strain rats were left to age for up to 24 months. One group of rats was subjected to a diet supplemented with ALA and SOD for 8 weeks, while another group was used as a positive control and not subjected to any dietary treatment. To assess the cytoprotective effects of the antioxidants, a morphological analysis was carried out on sections of retina and optic nerve head, stained with haematoxylin-eosin, followed by an analysis of the modifications to nuclear DNA detected by the TUNEL technique. The lipid peroxidation assay was used to assess the damage induced by oxidative stress at cell membrane level. The molecules involved in apoptosis mediated by oxidative stress, such as caspase-3 and inducible nitric oxide synthase, were also assayed by immunolocalization and western blot. ALA and SOD are able to counteract senile neurodegenerative deterioration to the retina and optic nerve. Indeed, the combination of these antioxidant molecules can reduce oxidative stress levels and thus prevent both nuclear degradation and subsequent cell death.

Dietary intake of Curcuma longa and Emblica officinalis increases life span in Drosophila melanogaster

Intake of food and nutrition plays a major role in affecting aging process and longevity. However, the precise mechanisms underlying the ageing process are still unclear. To this respect, diet has been considered to be a determinant of ageing process. In order to better illustrate this, we used Drosophila melanogaster as a model and fed them orally with different concentrations of two commonly used Indian medicinal plant products, Curcuma longa (rhizome) and Emblica officinalis (fruit). The results revealed significant increase in life span of Drosophila flies on exposure to both the plant products, more efficiently by C. Longa than by E. officinalis. In order to understand whether the increase in lifespan was due to high-antioxidant properties of these medicinal plants, we performed enzymatic assays to assess the SOD and catalase activities in case of both treated and control Drosophila flies. Interestingly, the results support the free radical theory of aging as both these plant derivatives show high reactive oxygen species (ROS) scavenging activities.

Superoxide dismutase1 levels in North Indian population with age-related macular degeneration

Aim. The aim of the study was to estimate the levels of superoxide dismutase1 (SOD1) in patients of age-related macular degeneration (AMD) and examine the role of oxidative stress, smoking, hypertension, and other factors involved in the pathogenesis of AMD. Methods. 115 AMD patients and 61 healthy controls were recruited for this study. Serum SOD1 levels were determined by ELISA and were correlated to various risk factors. Logistic regression model of authenticity, by considering SOD1 as independent variable, has been developed along with ROC curve. Results. The SOD1 levels were significantly higher in AMD patients as compared to those of the controls. The difference was not significant for wet and dry AMD. However, the difference was significant between wet AMD subtypes. Nonsignificance of the Hosmer-Lemeshow goodness of fit statistic (χ² = 10.516, df = 8, P = 0.231) indicates the appropriateness of logistic regression model to predict AMD. Conclusion. Oxidative stress in AMD patients may mount compensatory response resulting in increased levels of SOD1 in AMD patients. To predict the risk of AMD on the basis of SOD1, a logistic regression model shows authenticity of 78%, and area under the ROC curve (0.827, P = .0001) with less standard error of 0.033 coupled with 95% confidence interval of 0.762–0.891 further validates the model.

Detection, distribution and characterization of novel superoxide dismutases from Yersinia enterocolitica Biovar 1A

BACKGROUND

Superoxide dismutases (SODs) cause dismutation of superoxide radicals to hydrogen peroxide and oxygen. Besides protecting the cells against oxidative damage by endogenously generated oxygen radicals, SODs play an important role in intraphagocytic survival of pathogenic bacteria. The complete genome sequences of Yersinia enterocolitica strains show presence of three different sod genes. However, not much is known about the types of SODs present in Y. enterocolitica, their characteristics and role in virulence and intraphagocytic survival of this organism.

METHODOLOGY/PRINCIPAL FINDINGS

This study reports detection and distribution of the three superoxide dismutase (sodA, sodB and sodC) genes in 59 strains of Y. enterocolitica and related species. The majority (94%) of the strains carried all three genes and constitutive expression of sodA and sodB was detected in 88% of the strains. Expression of sodC was not observed in any of the strains. The sodA, sodB and sodC genes of Y. enterocolitica were cloned in pET28a (+) vector. Recombinant SodA (82 kDa) and SodB (21 kDa) were expressed as homotetramer and monomer respectively, and showed activity over a broad range of pH (3.0-8.0) and temperature (4-70°C). SodA and SodB showed optimal activity at 4°C under acidic pH of 6.0 and 4.0 respectively. The secondary structures of recombinant SodA and SodB were studied using circular dichroism. Production of YeSodC was not observed even after cloning and expression in E. coli BL21(DE3) cells. A SodA(-) SodB(-) Escherichia coli strain which was unable to grow in medium supplemented with paraquat showed normal growth after complementation with Y. enterocolitica SodA or SodB.

CONCLUSIONS/SIGNIFICANCE

This is the first report on the distribution and characterization of superoxide dismutases from Y. enterocolitica. The low pH optima of both SodA and SodB encoded by Y. enterocolitica seem to implicate their role in acidic environments such as the intraphagocytic vesicles.

The nature and mechanism of superoxide production by the electron transport chain: Its relevance to aging

Most biogerontologists agree that oxygen (and nitrogen) free radicals play a major role in the process of aging. The evidence strongly suggests that the electron transport chain, located in the inner mitochondrial membrane, is the major source of reactive oxygen species in animal cells. It has been reported that there exists an inverse correlation between the rate of superoxide/hydrogen peroxide production by mitochondria and the maximum longevity of mammalian species. However, no correlation or most frequently an inverse correlation exists between the amount of antioxidant enzymes and maximum longevity. Although overexpression of the antioxidant enzymes SOD1 and CAT (as well as SOD1 alone) have been successful at extending maximum lifespan in Drosophila, this has not been the case in mice. Several labs have overexpressed SOD1 and failed to see a positive effect on longevity. An explanation for this failure is that there is some level of superoxide damage that is not preventable by SOD, such as that initiated by the hydroperoxyl radical inside the lipid bilayer, and that accumulation of this damage is responsible for aging. I therefore suggest an alternative approach to testing the free radical theory of aging in mammals. Instead of trying to increase the amount of antioxidant enzymes, I suggest using molecular biology/transgenics to decrease the rate of superoxide production, which in the context of the free radical theory of aging would be expected to increase longevity. This paper aims to summarize what is known about the nature and mechanisms of superoxide production and what genes are involved in controlling the rate of superoxide production.

Thioredoxin, oxidative stress, cancer and aging

The Free Radical or Oxidative Stress Theory of Aging is one of the most popular theories in aging research and has been extensively studied over the past several decades. However, recent evidence using transgenic/knockout mice that overexpress or down-regulate antioxidant enzymes challenge the veracity of this theory since the animals show no increase or decrease in lifespan. These results seriously call into question the role of oxidative damage/stress in the aging process in mammals. Therefore, the theory requires significant modifications if we are to understand the relationship between aging and the regulation of oxidative stress. Our laboratory has been examining the impacts of thioredoxins (Trxs), in the cytosol and mitochondria, on aging and age-related diseases. Our data from mice that are either up-regulating or down-regulating Trx in different cellular compartments, that is, the cytosol or mitochondria, could shed some light on the role of oxidative stress and its pathophysiological effects. The results generated from our lab and others may indicate that: 1) changes in oxidative stress and the redox state in the cytosol, mitochondria or nucleus might play different roles in the aging process; 2) the role of oxidative stress and redox state could have different pathophysiological consequences in different tissues/cells, for example, mitotic vs. post-mitotic; 3) oxidative stress could have different pathophysiological impacts in young and old animals; and 4) the pathophysiological roles of oxidative stress and redox state could be controlled through changes in redox-sensitive signaling, which could have more diverse effects on pathophysiology than the accumulation of oxidative damage to various molecules. To critically test the role of oxidative stress on aging and age-related diseases, further study is required using animal models that regulate oxidative stress levels differently in each cellular compartment, each tissue/organ, and/or at different stages of life (young, middle and old) to change redox sensitive signaling pathways.

Healthy aging - insights from Drosophila

Human life expectancy has nearly doubled in the past century due, in part, to social and economic development, and a wide range of new medical technologies and treatments. As the number of elderly increase it becomes of vital importance to understand what factors contribute to healthy aging. Human longevity is a complex process that is affected by both environmental and genetic factors and interactions between them. Unfortunately, it is currently difficult to identify the role of genetic components in human longevity. In contrast, model organisms such as C. elegans, Drosophila, and rodents have facilitated the search for specific genes that affect lifespan. Experimental evidence obtained from studies in model organisms suggests that mutations in a single gene may increase longevity and delay the onset of age-related symptoms including motor impairments, sexual and reproductive and immune dysfunction, cardiovascular disease, and cognitive decline. Furthermore, the high degree of conservation between diverse species in the genes and pathways that regulate longevity suggests that work in model organisms can both expand our theoretical knowledge of aging and perhaps provide new therapeutic targets for the treatment of age-related disorders.

Expression of multiple copies of mitochondrially targeted catalase or genomic Mn superoxide dismutase transgenes does not extend the life span of Drosophila melanogaster

The simultaneous overexpression of multiple copies of Mn superoxide dismutase (SOD) and ectopic catalase (mtCat) transgenes in the mitochondria of the fruit fly, Drosophila melanogaster, was shown previously to diminish the life span. The hypothesis tested in this study was that this effect was due primarily to the presence of one or the other transgene. An alternative hypothesis was that both transgenes have additive, negative effects. Crosses were performed between five pairs of transgenic lines containing single-copy insertions of mtCat, Mn SOD, or P element vector control transgenes at unique loci, and the life spans of progeny containing two mtCat, Mn SOD, or vector insertions were determined. Increasing amounts of mitochondrial catalase activity tended to be associated with decreases in mean life span. Overexpression of two copies of the genomic Mn SOD transgene had no effect on life span. The results do not support the hypothesis that enhanced mitochondrial SOD or catalase activity promotes longevity in flies.

Update on the oxidative stress theory of aging: does oxidative stress play a role in aging or healthy aging?

The oxidative stress theory of aging predicts that manipulations that alter oxidative stress/damage will alter aging. The gold standard for determining whether aging is altered is life span, i.e., does altering oxidative stress/damage change life span? Mice with genetic manipulations in their antioxidant defense system designed to directly address this prediction have, with few exceptions, shown no change in life span. However, when these transgenic/knockout mice are tested using models that develop various types of age-related pathology, they show alterations in progression and/or severity of pathology as predicted by the oxidative stress theory: increased oxidative stress accelerates pathology and reduced oxidative stress retards pathology. These contradictory observations might mean that (a) oxidative stress plays a very limited, if any, role in aging but a major role in health span and/or (b) the role that oxidative stress plays in aging depends on environment. In environments with minimal stress, as expected under optimal husbandry, oxidative damage plays little role in aging. However, under chronic stress, including pathological phenotypes that diminish optimal health, oxidative stress/damage plays a major role in aging. Under these conditions, enhanced antioxidant defenses exert an "antiaging" action, leading to changes in life span, age-related pathology, and physiological function as predicted by the oxidative stress theory of aging.

Is there more to aging than mitochondrial DNA and reactive oxygen species?

With the aging of the population, we are seeing a global increase in the prevalence of age-related disorders, especially in developed countries. Chronic diseases disproportionately affect the older segment of the population, contributing to disability, a diminished quality of life and an increase in healthcare costs. Increased life expectancy reflects the success of contemporary medicine, which must now respond to the challenges created by this achievement, including the growing burden of chronic illnesses, injuries and disabilities. A well-developed theoretical framework is required to understand the molecular basis of aging. Such a framework is a prerequisite for the development of clinical interventions that will constitute an efficient response to the challenge of age-related health issues. This review critically analyzes the experimental evidence that supports and refutes the Free Radical/Mitochondrial Theory of Aging, which has dominated the field of aging research for almost half a century.

Superoxide dismutase is regulated by LAMMER kinase in Drosophila and human cells

LAMMER kinases (also known as CDC-2-like or CLKs) are a family of dual specificity serine/threonine protein kinases that are found in all sequenced eukaryotic genomes. In the fission yeast, Schizosaccharomyces pombe, the LAMMER kinase gene, Lkh1, positively regulates the expression of the antioxidant defense genes, superoxide dismutase 1 (sod1+, CuZn-SOD) and catalase (ctt1+, CAT). We have shown that mutations in the Drosophila LAMMER kinase gene, Darkener of apricot (Doa), protect against the decrease in life span caused by the reactive oxygen species (ROS) generator paraquat, and at the same time show an increase in cytoplasmic (CuZn-Sod or SOD1) and mitochondrial superoxide dismutase (Mn-Sod or SOD2) protein levels and activity. The siRNA-mediated knock down of the human LAMMER kinase gene, CLK-1, in HeLa and MCF-7 human cell lines leads to an increase in both SOD1 activity and mRNA transcript levels. These data suggest that SOD1 is negatively regulated by LAMMER kinases in Drosophila and human cell lines and that this regulation may be conserved during evolution.

Phenotypic effects of familial amyotrophic lateral sclerosis mutant Sod alleles in transgenic Drosophila

A subset of patients suffering from familial amyotrophic lateral sclerosis (FALS) exhibit point mutations in the gene encoding Cu-Zn superoxide dismutase [superoxide:superoxide oxidoreductase, EC (SOD)]. The human wild-type and five FALS Sod mutant transgenes were introduced into the fruit fly, Drosophila melanogaster, in a Cu-Zn Sod null background. Sod null flies had dramatically decreased life span, glutathione and methionine content, fertility, locomotor activity, and resistance to hyperoxic stress, compared with wild-type controls. All of these phenotypic manifestations were rescued fully by a single human wild-type allele, expressing 5-10% of wild-type SOD activity. Full recovery of wild-type life span was also observed when human mutant and wild-type alleles were placed together in the fly Sod null background. The FALS Sod mutations alone caused a recessive phenotype, usually involving low or undetectable levels of SOD activity, in which: (i) full restoration of the wild-type phenotype was observed among young adults, and (ii) older adults exhibited a sudden increase in oxidative stress, accompanied by physiological impairment of abrupt onset, and followed by premature death. Thus, the minimal SOD activity associated with the FALS Sod mutations appears to determine longevity, not by chronically increasing oxidative stress, but by limiting the time in which a viable redox environment can be maintained. However, the dominant gain of function by mutant SOD, which occurs in human patients and in the transgenic mouse model of FALS, is not observed in Drosophila.

Prolongation of life in an experimental model of aging in Drosophila melanogaster

(R)-Deprenyl, the archetypical monoamine oxidase-B inhibitor, has been shown to increase life-span in a number of species. Although many theories for this effect have been suggested, for example, an increase in superoxide dismutase (SOD) activity, the mechanism of action has yet to be elucidated. To investigate this phenomenon, we have examined the effects of (R)-deprenyl, and some aliphatic propargylamines, in an experimental aging model in Drosophila melanogaster. Both wild-type Oregon-R type flies, as well as a SOD knock-out mutant strain were used. Flies obtained from a series of paired mates were divided equally among treatment groups. In all studies, flies were treated for the duration of life following adult emergence. The aging model consists of substitution of sucrose with galactose in the regular food media of the flies. Initial experiments confirmed that such a substitution resulted in a significant (p < 0.01, Breslow test) reduction in mean and maximal life-span of flies, an effect not due to nutrient deprivation. Inclusion of (R)-deprenyl and the aliphatic propargylamines in the media, at average daily doses in the range 0.5-1 ng/fly/day, led to a significant increase in mean and maximal life-span of galactose-treated, but not control flies. This effect was seen in both wild-type and mutant flies.

FLP recombinase-mediated induction of Cu/Zn-superoxide dismutase transgene expression can extend the life span of adult Drosophila melanogaster flies

Yeast FLP recombinase was used in a binary transgenic system ("FLP-OUT") to allow induced overexpression of catalase and/or Cu/Zn-superoxide dismutase (Cu/ZnSOD) in adult Drosophila melanogaster. Expression of FLP recombinase was driven by the heat-inducible hsp70 promoter. Once expressed, FLP catalyzed the rearrangement and activation of a target construct in which expression of catalase or Cu/ZnSOD cDNAs was driven by the constitutive actin5C promoter. In this way a brief heat pulse (120 or 180 min, total) of young adult flies activated transgene expression for the rest of the life span. FLP-OUT allows the effects of induced transgene expression to be analyzed in control (no heat pulse) and experimental (heat pulse) populations with identical genetic backgrounds. Under the conditions used, the heat pulse itself always had neutral or slightly negative effects on the life span. Catalase overexpression significantly increased resistance to hydrogen peroxide but had neutral or slightly negative effects on the mean life span. Cu/ZnSOD overexpression extended the mean life span up to 48%. Simultaneous overexpression of catalase with Cu/ZnSOD had no added benefit, presumably due to a preexisting excess of catalase. The data suggest that oxidative damage is one rate-limiting factor for the life span of adult Drosophila. Finally, experimental manipulation of the genetic background demonstrated that the life span is affected by epistatic interactions between the transgene and allele(s) at other loci.

Lower intracellular hydrogen peroxide levels in cells overexpressing CuZn-superoxide dismutase

Transfection of V79 Chinese hamster cells produced clones in which CuZn-superoxide dismutase (CuZn-SOD) activities were 2.2- to 3. 5-fold higher than in the parental cells. An overall reduction of antioxidant enzyme activities and both total and oxidized glutathione levels had been found in these clones. Aconitase activities in these cells were determined to indirectly measure the O2- steady-state levels. As expected, in cells overexpressing CuZn-SOD, both total and cytosolic aconitase activities have increased. Because these clones showed reduced oxidized glutathione contents, it is unlikely that they present higher H2O2 steady-state levels as a consequence of the higher SOD levels. This was confirmed by measuring H2O2 steady-state levels in cells by flow cytometric analysis of 2',7'-dichlorofluorescein diacetate-treated cells. Despite the decreased antioxidant defenses, three of the clones overexpressing CuZn-SOD showed reduced H2O2 steady-state levels. These reduced H2O2 steady-state levels were found even when the cells were treated with the O2- generator 2,3-dimethoxy-1, 4-naphthoquinone. These data provide in vivo support for the hypothesis proposed by Liochev and Fridovich [Liochev, S. I. & Fridovich, I. (1994) Free Radical Biol. Med. 16, 29-33] that O2- dismutation prevents the formation of higher H2O2 levels by other reactions.

Muscle-specific expression of Drosophila hsp70 in response to aging and oxidative stress

Induction of Drosophila hsp70 protein was detected during aging in flight muscle and leg muscle in the absence of heat shock, using an hsp70-specific monoclonal antibody, and in transgenic flies containing hsp70-beta-galactosidase fusion protein reporter constructs. While hsp70 and reporter proteins were induced during aging, hsp70 message levels were not, indicating that aging-specific induction is primarily posttranscriptional. In contrast, hsp22 and hsp23 were found to be induced during aging at the RNA level and with a broader tissue distribution. The same muscle-specific hsp70 reporter expression pattern was observed in young flies mutant for catalase (H2O2:H2O2 oxidoreductase, EC 1.11.1.6). In catalase (cat) hypomorphic lines where flies survived to older ages, the time course of hsp70 reporter expression during aging was accelerated, and the initial and ultimate levels of expression were increased. The hsp70 reporter was also induced in young flies mutant for copper/zinc superoxide dismutase (superoxide:superoxide oxidoreductase, EC 1.15.1.1). Taken together, the results suggest that aging-specific hsp70 expression may be a result of oxidative damage.

Characterization of the manganese superoxide dismutase cDNA and gene from the human parasite Onchocerca volvulus

The manganese-containing superoxide dismutase (MnSOD) is a major component of the cellular defence mechanisms against the toxic effects of the superoxide radical. Within the framework of studies on anti-oxidant enzymes and their protective role in the human parasitic nematode Onchocerca volvulus, sequences encoding the MnSOD were isolated and examined in this study. Degenerate primers were designed based upon conserved regions of MnSOD sequences from other organisms, and were used in PCR on reverse-transcribed O. volvulus total RNA and genomic DNA to identify partial cDNA and genomic DNA fragments encoding the O. volvulus MnSOD (OvMnSOD). The genomic DNA PCR product was used to screen an O. volvulus adult worm lambda unizap II cDNA library and the nucleotide sequence of the longest clone determined. The complete 5'-end of the OvMnSOD cDNA was obtained using the rapid amplification of cDNA ends (RACE) procedure with O. volvulus total RNA and was found to possess a spliced leader sequence at the 5'-terminus. The deduced primary sequence encodes a 25 kDa protein, which has the conserved residues required for enzyme activity and metal binding. The 24 N-terminal amino acids encoded by the OvMnSOD cDNA comprise a putative mitochondrial transit peptide. The OvMnSOD gene was also isolated from an O. volvulus adult worm lambda fix II genomic library, a restriction map was constructed and the nucleotide sequence determined. The OvMnSOD gene was found to possess five exons and four introns with consensus splice-site junctions. Potential regulatory elements were identified in the 5' genomic flanking sequence. Southern-blot analysis with total worm genomic DNA indicates a single-copy gene, with a restriction pattern consistent with that of the isolated gene.

Phenotypic rescue by a bovine transgene in a Cu/Zn superoxide dismutase-null mutant of Drosophila melanogaster

Null mutants for Cu/Zn superoxide dismutase (CuZnSOD) in Drosophila melanogaster are male sterile, have a greatly reduced adult life span, and are hypersensitive to paraquat. We have introduced a synthetic bovine CuZnSOD transgene under the transcriptional control of the D. melanogaster 5C actin promoter into a CuZnSOD-null mutant of D. melanogaster. This was carried out by P-element-mediated transformation of the Drosophila-bovine CuZnSOD transgene into a CuZnSOD+ recipient strain followed by genetic crossing of the transgene into a strain carrying the CuZnSOD-null mutation, cSODn108. The resulting transformants express bovine CuZnSOD exclusively to about 30% of normal Drosophila CuZnSOD levels. Expression of the Drosophila-bovine CuZnSOD transgene in the CuZnSOD-null mutant rescues male fertility and resistance to paraquat to apparently normal levels. However, adult life span is restored to only 30% of normal, and resistance to hyperoxia is 90% of that found in control flies. This striking differential restoration of pleiotropic phenotypes could be the result of a threshhold of CuZnSOD expression necessary for normal male fertility and resistance to the toxicity of paraquat or hyperoxia which is lower than the threshold required to sustain a normal adult life span. Alternatively, the differential rescue of fertility, resistance to active oxygen, and life span might indicate different cell-specific transcriptional requirements for these functions which are normally provided by the control elements of the native CuZnSOD gene but are only partly compensated for by the transcriptional control elements of the actin 5C promoter.

Phenotypic rescue by a bovine transgene in a Cu/Zn superoxide dismutase-null mutant of Drosophila melanogaster

Null mutants for Cu/Zn superoxide dismutase (CuZnSOD) in Drosophila melanogaster are male sterile, have a greatly reduced adult life span, and are hypersensitive to paraquat. We have introduced a synthetic bovine CuZnSOD transgene under the transcriptional control of the D. melanogaster 5C actin promoter into a CuZnSOD-null mutant of D. melanogaster. This was carried out by P-element-mediated transformation of the Drosophila-bovine CuZnSOD transgene into a CuZnSOD+ recipient strain followed by genetic crossing of the transgene into a strain carrying the CuZnSOD-null mutation, cSODn108. The resulting transformants express bovine CuZnSOD exclusively to about 30% of normal Drosophila CuZnSOD levels. Expression of the Drosophila-bovine CuZnSOD transgene in the CuZnSOD-null mutant rescues male fertility and resistance to paraquat to apparently normal levels. However, adult life span is restored to only 30% of normal, and resistance to hyperoxia is 90% of that found in control flies. This striking differential restoration of pleiotropic phenotypes could be the result of a threshhold of CuZnSOD expression necessary for normal male fertility and resistance to the toxicity of paraquat or hyperoxia which is lower than the threshold required to sustain a normal adult life span. Alternatively, the differential rescue of fertility, resistance to active oxygen, and life span might indicate different cell-specific transcriptional requirements for these functions which are normally provided by the control elements of the native CuZnSOD gene but are only partly compensated for by the transcriptional control elements of the actin 5C promoter.