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R Arking

Publications and source records attributed to R Arking.

At least 19 recordsLinked to original sources
PubMed2001

Direct selection for paraquat resistance in Drosophila results in a different extended longevity phenotype.

When normal-lived Ra strain Drosophila were indirectly selected for longevity, they gave rise to long-lived La strain animals with lower oxidized protein and lipid levels that were temporally coincident with higher antioxidant activities. We wanted to determine whether it was possible to create long-lived animals by a direct selection for increased antioxidant activities. Using the same Ra strain, we selected them over 24 generations for increased resistance to paraquat. Selection was successful: the paraquat-resistant flies had a fourfold increase in their LT(50) (mean lethal time) values. Their extended longevity pattern differs from that of the La strain. The paraquat-resistant animals also have a lower level of antioxidant activity, an increased total P450 enzyme activity level, an altered pattern of energy metabolism, and a significantly lower developmental viability. We interpret these findings as suggesting that similar stress response phenotypes may be generated by different molecular mechanisms, some of which may generate very different types of extended longevity phenotypes.

Animals↗
PubMed2000

Identical longevity phenotypes are characterized by different patterns of gene expression and oxidative damage.

Some years ago we applied simultaneously an identical regime of selection for late-life reproduction to several normal-lived sister lines (Ra and Rb) so as to produce several selected long-lived sister lines (La and Lb). The long-lived La and Lb sister lines had statistically identical longevity phenotypes and paraquat resistance phenotypes; however, we noticed some statistically different responses of the two strains at the biochemical level. Extensive work with the La strain showed that transcriptional alterations in antioxidant gene expression are robustly associated with its extended longevity. We decided to critically test the assumption of phenotypic equivalence by subjecting the Lb strain to the same series of molecular assays as was the La strain. The two sister strains are characterized by significantly different mechanisms and patterns of antioxidant gene expression, antioxidant enzyme activity, and oxidative damage. We find that the Lb strain appears to depend on the transcriptional activation of different genes than does the La strain, and on a post-translational up-regulation of at least one other antioxidant defense gene. The phenotypic equivalence observed at the organism level need not hold at the molecular genetic level. This finding suggests that there is more than one molecular mechanism by which antioxidant defense genes can bring about an increased resistance to oxidative stress. The theoretical and empirical implications of these findings are discussed.

Animals↗
PubMed2000

Forward and reverse selection for longevity in Drosophila is characterized by alteration of antioxidant gene expression and oxidative damage patterns.

Patterns of antioxidant gene expression and of oxidative damage were measured throughout the adult life span of a selected long-lived strain (La) of Drosophila melanogaster and compared to that of their normal-lived progenitor strain (Ra). Extended longevity in the La strain is correlated with enhanced antioxidant defense system gene expression, accumulation of CuZnSOD protein, and an increase in ADS enzyme activities. Extended longevity is strongly associated with a significantly increased resistance to oxidative stress. Reverse-selecting this long-lived strain for shortened longevity (RevLa strain) yields a significant decrease in longevity accompanied by reversion to normal levels of its antioxidant defense system gene expression patterns and antioxidant enzyme patterns. The significant effects of forward and reverse selection in these strains seem limited to the ADS enzymes; 11 other enzymes with primarily metabolic functions show no obvious effect of selection on their activity levels whereas six other enzymes postulated to play a role in flux control may actually be involved in NADPH reoxidation and thus support the enhanced activities of the ADS enzymes. Thus, alterations in the longevity of these Drosophila strains are directly correlated with corresponding alterations in; 1) the mRNA levels of certain antioxidant defense system genes; 2) the protein level of at least one antioxidant defense system gene; 3) the activity levels of the corresponding antioxidant defense system enzymes, and 4) the ability of the organism to resist the biological damage arising from oxidative stress.

Acatalasia↗
PubMed2000

Extended longevity in Drosophila is consistently associated with a decrease in developmental viability.

It has proven relatively easy to select normal-lived strains of Drosophila for extended longevity in the laboratory. Long-lived strains have not been observed in the wild as yet. Of the various life-history traits that have been investigated for their role in modulating the evolution of extended longevity, none have yet shown a consistent or convincing relationship. Other than developmental time, the traits usually investigated in this regard are those associated with the adult phase of the life cycle. We assayed developmental timing and viability in six pairs of normal- and long-lived strains, four pairs of which are from previously described strains and two pairs of which are new strains that have been independently and recently selected. We find that the life-history trait most obviously associated with all our long-lived strains is a significantly reduced developmental viability, with the long-lived strains' having as much as twice the developmental lethality as do any of the normal-lived strains. The long-lived strains also pupate closer to the food, a behavior known to decrease fitness. Thus the reduced fitness of the long-lived strains appears to be due to both physiological and behavioral factors and may well explain why long lived strains are not usually found in the wild. The extension of longevity involves costs as well as benefits that, in this case, are borne by different individuals.

Animals↗
PubMed1998

Immunological confirmation of elevated levels of CuZn superoxide dismutase protein in an artificially selected long-lived strain of Drosophila melanogaster.

Oxidative stress-induced damage is a major causal factor leading to the loss of function characteristic of the aging process. Various antioxidant defenses are marshalled by the organism so as to combat this oxidative damage and delay the onset of senscence. CuZnSOD is one of the major antioxidant enzymes and has been shown to play an important role in the extended longevity of Drosophila melanogaster. Although assays exist with which to measure the CuZnSOD RNA prevalence and enzyme activity, there existed no antibodies that permitted the measurement of the actual amount of Drosophila enzyme protein present. Development of such a tool would enhance our ability to understand mechanisms of antioxidant gene expression in this organism. We have developed a polyclonal antibody against synthetic SOD peptides that is specific for Drosophila CuZnSOD as shown by Western blots. It is very sensitive when tested against native Drosophila CuZnSOD protein. Its use in our experimental system confirms the prior RNA and enzyme activity measurements that indicate that our genetically selected long-lived strain has significantly higher levels of CuZnSOD protein than does the appropriate control strain.

Animals↗
PubMed1995

Comparative biochemical and stress analysis of genetically selected Drosophila strains with different longevities.

We have performed a comparative analysis of the effects of age of reproduction on the biochemical (protein, lipid, and glycogen content) and stress resistance (ability to survive starvation, desiccation, and exogenous paraquat) parameters on 10 sister lines of five different Drosophila strains. Four pairs of these sister lines were selected under different regimens for either early or delayed reproduction; the fifth pair was maintained in a nonselected state and served as the baseline strain to which all others were compared. It is generally accepted that the early regimens give rise to short-lived phenotypes, whereas the delayed regimens give rise to long-lived phenotypes. Our results suggest that a mechanism involving lipid and starvation resistance is not operative in our long-lived strains. In addition, a mechanism involving glycogen content and desiccation resistance is only weakly supported. Finally, there is strong support for a mechanism that gives rise to enhanced paraquat resistance and therefore may involve regulatory changes in the pattern of ADS gene expression. In addition, the 15-day early age of reproduction regimen (M type) shows qualitatively similar responses to that of the late age at reproduction regimen (L type). These results suggest that correlations between biochemical traits and longevity must be interpreted with caution. We discuss possible reasons for these results, including the possibility of multiple mechanisms, each leading to a different extended longevity phenotype.

Animals↗
PubMed1995

A coordinate upregulation of antioxidant gene activities is associated with the delayed onset of senescence in a long-lived strain of Drosophila.

The extended longevity phenotype (ELP) characteristic of our selected long-lived strain of Drosophila is brought about by a delayed onset of senescence which occurs in the young (5-7 day) adult. Genetically competent animals will not express the resistance to exogenous paraquat characteristic of the ELP as adults unless they develop in a particular larval environment. This induction leads to a series of coordinated increases in their antioxidant defense system mRNA levels and in their enzyme activities. Not all genes show such changes. These increases in antioxidant gene product levels appear to be functional, as witnessed by the fact that the long-lived animals show an increase in their resistance to exogenous paraquat at that same time. Aminotriazole-induced destruction of catalase activity in the long-lived animals results in the loss of their increased resistance to paraquat. The non-induced control animals do not show such elevations in antioxidant defense system elevations, and shortly thereafter show a significant decline in their paraquat resistance followed by the subsequent loss of certain behavioral traits diagnostic of senescence.

Aging↗
PubMed1995

Selection for increased longevity in Drosophila melanogaster: a reply to Lints.

An important tool in the genetic analysis of longevity and aging in Drosophila melanogaster is the use of strains selected directly for late-age reproduction and indirectly for extended longevity. Following some initial failures to select for extended longevity, there are now a number of laboratories which have successfully selected for long life, using the techniques of late-age reproduction as well as selection for stress resistance. Baret and Lints [Gerontology 1993;39:252-259] have recently cast doubt on the reality of a number of these selected strains, including our own, suggesting that the difference in longevity between the long-lived and normal-lived strains disappears when the data are examined as a function of the number of days after the beginning of the selection experiment instead of as a function of the number of generations. With regard to our selected lines, they based their analysis on a subset of the published data dealing with these strains, and which covered 21 generations, or 40 months, of selection. We now present data for over 70 generations, or 155 months, of selection and maintenance. The Baret-Lints hypothesis makes two strong predictions, namely that (1) the longevity difference between the several strains should disappear when the data are replotted according to their fashion, and (2) there should be no other significant biological difference between the strains. Our data falsifies both of these predictions. The Baret-Lints hypothesis is flawed and should be disregarded.(ABSTRACT TRUNCATED AT 250 WORDS)

Animals↗
PubMed1993

Genetic and environmental factors regulating the expression of an extended longevity phenotype in a long lived strain of Drosophila.

We have demonstrated that the expression of the ELP in our strains is the outcome of a genetically determined, environmentally modulated, event dependent, developmental process. Given the appropriate genetic and environmental conditions, we observe an early acting temporal progression of alterations in specific gene activity patterns which appear to give rise to functional phenotypic changes. The observed patterns are consistent with the interpretations drawn from our chromosome substitution and biomarker experiments. The interaction of specific environmental and genetic factors is sufficient to explain the observed plasticity of longevity in our L strain. Independently derived long lived strains may have altered different combinations of physiological mechanisms so as to give rise to a statistically equivalent ELP. Theoretically based conclusions obtained from only one set of sister strains may be difficult to extrapolate to other strains. Future work will involve the experimental verification of the genetic-environmental circuitry discussed here, using novel molecular genetic techniques to define, characterize, and isolate the genes involved in the expression of the ELP.

Animals↗
PubMed1993

Chromosomal localization and regulation of the longevity determinant genes in a selected strain of Drosophila melanogaster.

A controlled chromosome substitution experiment was performed on a strain (NDC-L) selected for long life to determine if the genes responsible for the extended-longevity phenotype could be localized to any particular chromosome(s). All 27 different possible combinations of the three major chromosomes of Drosophila melanogaster were constructed and longevities were determined on 3875 individual animals of both sexes and analysed. The results are statistically significant and demonstrate that mean longevity is specified primarily by recessive genes on the third chromosome (c3). The extended longevity phenotype (ELP) is only expressed in those lines which are homozygous for the NDC-L type c3. Loci on the first (c1) and second (c2) chromosomes interact, both positively (c1) and negatively (c2), respectively, such that c1 represses c2 which in turn represses c3. The ELP is fully expressed in the mutual presence and mutual absence of c1 and c2. The significance of these results is discussed in the context of broader categories of molecular genetic mechanisms suggested previously to be involved in the modulation of longevity in Drosophila.

Animals↗
PubMed1993

Larval regulation of adult longevity in a genetically-selected long-lived strain of Drosophila.

Our previous work has shown that the major genes involved in the expression of the extended-longevity phenotype are located on the third chromosome. Furthermore, their expression is negatively and positively influenced by chromosomes 2 and 1, respectively. In this report we show that the expression of the extended-longevity phenotype is dependent on the larval environment. A controlled chromosome substitution experiment was carried out using a strain selected for long life (L) and its parent (R) strain. Twenty different combinations of the three major chromosomes were conducted and their longevities were determined under both high (HD) and low (LD) larval density conditions. The extended-longevity phenotype was only expressed under HD conditions. The chromosome interactions were not apparent under LD conditions. Density-shift experiments delineate a critical period for expression of the extended-longevity phenotype, extending from 60 h after egg laying (AEL) to 96 h AEL, during which the developing animal must be exposed to HD conditions if the extended-longevity phenotype is to be expressed. The change from HD to LD conditions is accompanied by statistically significant increases in body weight. The possible role of a dietary restriction phenomenon is examined and the implications of these findings discussed. It is now apparent, however, that the extended-longevity phenotype in Drosophila is a developmental genetic process.

Animals↗
PubMed1991

Elevated paraquat resistance can be used as a bioassay for longevity in a genetically based long-lived strain of Drosophila.

A long-lived (L) strain of Drosophila melanogaster, derived from a normal-lived (R) strain by artificial selection, has a significantly different adult longevity. Previous work has shown that 1) the two strains age in the same manner, 2) the major genes responsible for much of the L strain's extended longevity are located on the 3rd chromosome, and 3) the extended longevity phenotype is significantly modulated by the larval environment. In this report, we investigate the resistance of the L and R strains to the lethal effects of dietary paraquat. We show that, within the limitations of our described chromosomal and environmental manipulations, the extended longevity phenotype always accompanies the phenotype of elevated paraquat resistance. In addition, reversed selection applied to the L strain results in the simultaneous decrease of both life span and paraquat resistance. Thus, the presence or absence of the latter phenotype may be used as a bioassay for the presence or absence of the extended longevity phenotype, without any necessary implication of causality. Use of this bioassay should greatly speed up the genetic analysis of this system by allowing us to identify long-lived animals at a young age. Finally, we show that the age-related loss of elevated paraquat resistance in both strains precedes all the other age-related functional decrements which we have previously noted in this system.

Animals↗
PubMed1990

Genetic alteration of normal aging processes is responsible for extended longevity in Drosophila.

The first step in a genetic analysis of aging is to identify and characterize the genetic mutants and their controls that will be used. Such mutants or strains are initially identified by their effect on the life span. Yet many genetic interventions are known to have some effect on the life span without necessarily affecting the aging process. It is therefore necessary to prove that one is actually dealing with an aging mutant before one draws strong inferences from the data. Casarett's rules provide an operational test for doing so, relying as they do on the comparison of aging bio-markers in the experimental and reference strains. We show that our previously described genetically based long-lived NDC-L strain and its normal-lived NDC-R control strain differ only in the chronological age of expression of two behavioral and three physiological functional age biomarkers. They do not differ in the sequence or the physiological age of expression of these biomarkers. These two strains comply with the Casarett rules and thereby comprise a valid tool with which to conduct a comparative genetic analysis of aging. The implications of the available data are discussed, including the possibility that aging in these strains of Drosophila melanogaster may be the result of a multiphasic developmental process.

Aging↗
PubMed1989

Patterns of amino acid incorporation in long-lived genetic strains of Drosophila melanogaster.

This study examined the age-dependent alterations in the in vivo incorporation of labeled amino acids into protein during the adult life spans of males and females obtained from genetically based long-lived and control strains of Drosophila melanogaster. All four groups tested showed significant decreases (ca. 50%) in the uptake of labeled amino acids as a function of age. Each of the four groups had their own characteristic temporal pattern of functional decrement. Both the long-lived and the control females have similar patterns of amino acid incorporation, but the onset of these changes is delayed by 10 to 20 days in long-lived animals. These alterations in protein synthesis appear to be related to corresponding changes in the female fecundity patterns of each strain. The male patterns differ from one another and from the female patterns, but they both show periods of high fluctuation early in life followed by a terminal period of relatively low and constant synthesis. These data are consistent with the view that the overall alterations in the longevity of these two strains are likely due to changes in the timing of particular events in the adult life cycle.

Aging↗
PubMed1989

Review of genetic investigations into the aging processes of Drosophila.

The field has progressed to the point where a genetic investigation of the aging processes in Drosophila can be viewed as constituting both a serious and a feasible research program. There now exists at least one single gene mutant which yields an accelerated aging phenotype, at least two single gene null mutants affecting enzymes implicated in regulating the aging process and resulting in premature death, and at least two strains created by artificial selection which produce extended-longevity phenotypes. In addition, genes such as adh have an indirect and interactive effect upon the animal's longevity and might also play an important role in the genetic regulation of this process. Although far from complete, some essential tools are now in place and are being used to answer some of the questions posed by Martin. Of the several theories put forth to explain aging in Drosophila, it appears as if the data best uphold the free radical and the protein synthesis/gene expression theories. It is entirely possible that these two theories are complementary aspects of a broader underlying process. The genetic mechanisms controlling these physiological processes clearly do so in concert with certain environmental factors. The net effect of their interactions may be the decreased synthetic and repair ability of the cell as suggested by Lamb and by Webster. It is probably true that aging and longevity are multicausal phenotypes. Our only hope of understanding such a complex phenotype is to dissect it genetically, one (or a few) genes at a time under rigidly controlled conditions. Thorough genetic description of each system will be the prerequisite to their molecular analysis. This will likely result in multiple explanations, ideally one for each system. Yet these multiple molecular genetic explanations may well enable us to see some commonality underlying the aging process in this organism. The fact that several different lines of evidence appear to be converging on a small number of theoretical explanations is an encouraging sign. We should also be heartened by the extraordinary increase in our knowledge of embryonic development in Drosophila as a result of just such a strategy. And we should not forget that the homeotic mutants which now play such a large role in the deciphering of embryogenesis were once classified as "complex loci" and that the then-accepted explanations gave no hint of the underlying molecular relationships. For now it is fair to conclude that aging in Drosophila may be viewed as a genetically-determined, environmentally-modulated, event-dependent process.(ABSTRACT TRUNCATED AT 400 WORDS)

Aging↗
PubMed1988

Metabolic rates in genetically based long lived strains of Drosophila.

The goal of these experiments was to determine if the increased longevity characteristics of our genetically selected long lived line of Drosophila could be attributed to metabolic differences. The data shows an inverse relationship between life span and temperature for both the long lived (L) and normal (R) strains; however, the higher longevity of the L strain relative to the R strain is not affected by these treatments. Therefore, the genetic factors unique to the L strain do not affect the same processes affected by the temperature treatments. A second set of experiments detected a linear relationship between the MDMR (mean daily metabolic rate) and the ambient adult temperature. However, at each temperature, the MDMR of either strain was statistically equivalent; a finding which demonstrates that an increased life span depends on something other than conservation of calories. A third set of experiments looked at the metabolic efficiency of the two strains and were not able to detect any statistically significant differences. The two strains appear to expend approximately equivalent numbers of calories per day in an approximately equivalent manner. These data are interpreted in the context both of a previously postulated genetic switch mechanism believed responsible for initiating the onset of senescence, and of contemporary reinterpretations of the "rate of living" theory which implicates the essential role of various anti-oxidant defense systems.

Aging↗
PubMed1987

Successful selection for increased longevity in Drosophila: analysis of the survival data and presentation of a hypothesis on the genetic regulation of longevity.

Long lived strains of Drosophila melanogaster have been generated via 25 generations of artificial selection. The mean and the maximum lifespans have been increased both absolutely as well as relative to the controls. The mean lifespan of the selected line now exceeds the maximum lifespan of the controls. The data shows that this increase is entirely accounted for by a genetically based delay in the onset of senescence. Identification and analysis of biomarker data involving reproductive functions supports this interpretation and leads to a suggestion of the processes involved in the lifespan extension. This increase in the duration of the pre-senescent period is under both genetic and environmental control. Senescence itself is not under genetic control and appears to occur stochastically. Selection for decreased longevity was unsuccessful, supporting the concept of a minimum species specific lifespan. A testable hypothesis regarding the biphasic mode of gene regulation of senescence is presented in which a gene-environment interaction takes place in larval life that results in a temporal reprogramming of other, presumably structural, genes which act in adult life at a time prior to the onset of senescence.

Aging↗