Decreased mitochondrial RNA levels without accumulation of mitochondrial DNA deletions in aging Drosophila melanogaster

Variegated expression of Hsp22 transgenic reporters indicates cell-specific patterns of aging in Drosophila oenocytes

The cytoplasmic chaperone gene Hsp70 and the mitochondrial chaperone gene Hsp22 are upregulated during normal aging in Drosophila in tissue-general patterns. In addition, Hsp22 reporters are dramatically upregulated during aging in a subset of the oenocytes (liver-like cells). Hsp22 reporter expression varied dramatically between individual oenocytes and between groups of oenocytes located in adjacent body segments, and was negatively correlated with accumulation of age pigment, indicating cell-specific and cell-lineage-specific patterns of oenocyte aging. Conditional transgenic systems were used to express 88 transgenes to search for trans-regulators of the Hsp70 and Hsp22 reporters during aging. The wingless gene increased tissue-general upregulation of both Hsp70 and Hsp22 reporters. In contrast, the mitochondrial genes MnSOD and Hsp22 increased expression of Hsp22 reporters in the oenocytes and decreased accumulation of age pigment in these cells. The data suggest that cell-specific and cell lineage-specific patterns of mitochondrial malfunction contribute to oenocyte aging.

Oxidative stress is not a major contributor to somatic mitochondrial DNA mutations

The accumulation of somatic mitochondrial DNA (mtDNA) mutations is implicated in aging and common diseases of the elderly, including cancer and neurodegenerative disease. However, the mechanisms that influence the frequency of somatic mtDNA mutations are poorly understood. To develop a simple invertebrate model system to address this matter, we used the Random Mutation Capture (RMC) assay to characterize the age-dependent frequency and distribution of mtDNA mutations in the fruit fly Drosophila melanogaster. Because oxidative stress is a major suspect in the age-dependent accumulation of somatic mtDNA mutations, we also used the RMC assay to explore the influence of oxidative stress on the somatic mtDNA mutation frequency. We found that many of the features associated with mtDNA mutations in vertebrates are conserved in Drosophila, including a comparable somatic mtDNA mutation frequency (∼10(-5)), an increased frequency of mtDNA mutations with age, and a prevalence of transition mutations. Only a small fraction of the mtDNA mutations detected in young or old animals were G∶C to T∶A transversions, a signature of oxidative damage, and loss-of-function mutations in the mitochondrial superoxide dismutase, Sod2, had no detectable influence on the somatic mtDNA mutation frequency. Moreover, a loss-of-function mutation in Ogg1, which encodes a DNA repair enzyme that removes oxidatively damaged deoxyguanosine residues (8-hydroxy-2'-deoxyguanosine), did not significantly influence the somatic mtDNA mutation frequency of Sod2 mutants. Together, these findings indicate that oxidative stress is not a major cause of somatic mtDNA mutations. Our data instead suggests that somatic mtDNA mutations arise primarily from errors that occur during mtDNA replication. Further studies using Drosophila should aid in the identification of factors that influence the frequency of somatic mtDNA mutations.

Aging perturbs 26S proteasome assembly in Drosophila melanogaster

Aging is associated with loss of quality control in protein turnover. The ubiquitin-proteasome pathway is critical to this quality control process as it degrades mutated and damaged proteins. We identified a unique aging-dependent mechanism that contributes to proteasome dysfunction in Drosophila melanogaster. Our studies are the first to show that the major proteasome form in old (43-47 days old) female and male flies is the weakly active 20S core particle, while in younger (1-32 days old) flies highly active 26S proteasomes are preponderant. Old (43-47 days) flies of both genders also exhibit a decline (approximately 50%) in ATP levels, which is relevant to 26S proteasomes, as their assembly is ATP-dependent. The steep declines in 26S proteasome and ATP levels were observed at an age (43-47 days) when the flies exhibited a marked drop in locomotor performance, attesting that these are "old age" events. Remarkably, treatment with a proteasome inhibitor increases ubiquitinated protein levels and shortens the life span of old but not young flies. In conclusion, our data reveal a previously unknown mechanism that perturbs proteasome activity in "old-age" female and male Drosophila most likely depriving them of the ability to effectively cope with proteotoxic damages caused by environmental and/or genetic factors.

Age-associated decline in mitochondrial respiration and electron transport in Drosophila melanogaster

The principal objective of the present study was to identify specific alterations in mitochondrial respiratory functions during the aging process. Respiration rates and the activities of electron transport chain complexes were measured at various ages in mitochondria isolated from thoraces of the fruit fly, Drosophila melanogaster, which consist primarily of flight muscles. The rates of state 3 respiration (ADP-stimulated), RCRs (respiratory control ratios) and uncoupled respiration rates decreased significantly as a function of age, using either NAD+- or FAD-linked substrates; however, there were no differences in state 4 respiration (ADP-depleted) rates. There was also a significant age-related decline in the activity of cytochrome c oxidase (complex IV), but not of the other mitochondrial oxidoreductases examined. Exposure of mitochondria isolated from young flies to low doses of KCN or NaAz (sodium azide), complex IV inhibitors, decreased cytochrome c oxidase activity and increased the production of H2O2. Collectively, these results support the hypothesis that impairment of mitochondrial respiration may be a causal factor in the aging process, and that such impairment may result from and contribute to increased H2O2 production in vivo.

Age-related RNA decline in adult Drosophila melanogaster

We investigated the correlation between age and total RNA levels in long-lived and control lines of Drosophila melanogaster. Total RNA was extracted at 10 ages from 1-63 days posteclosion from 3 inbred lines, with replication. Three different methods of RNA quantitation gave highly correlated estimates. Total RNA declined substantially with age, exhibiting a dramatic drop in the first few days of adult life. We find no evidence for a causal relationship between adult longevity and total RNA levels, since long-lived and control lines exhibited similar patterns of age-related RNA decline. These observations suggest that the dramatic decline in total RNA that occurs early in adult life does not explain the twofold differences in life span between lines. The pattern of age-specific decline coincides with published observations on age-specific metabolic rates, and suggests that 14-day-old flies are functionally senescent.

Drosophila melanogaster and the future of 'evo-devo' biology in space. Challenges and problems in the path of an eventual colonization project outside the earth

Space exploration, especially its future phase involving the International Space Station (ISS) makes possible the study of the effects on living systems of long-term expositions to such a strange environment. This phase is being initiated when Biological Sciences are crossing a no-return line into a new territory where the connection between phenotype and genotype may be finally made. We briefly review the paradoxical results obtained in Space experiments performed during the last third of the XX Century. They reveal that simple unicellular systems sense the absence of gravity changing their cytoskeletal organization and the signal transduction pathways, while animal development proceeds unaltered in these conditions, in spite of the fact that these processes are heavily involved in embryogenesis. Longer-term experiments possible in the ISS may solve this apparent contradiction. On the other hand, the current constraints on the scientific use of the ISS makes necessary the development of new hardware and the modification of current techniques to start taking advantage of this extraordinary technological facility. We discuss our advances in this direction using one of the current key biological model systems, Drosophila melanogaster. In addition, the future phase of Space exploration, possibly leading to the exploration and, may be, the colonization of another planet, will provide the means of performing interesting evolutionary experiments, studying how the terrestrial biological systems will change in their long-term adaptation to new, very different environments. In this way, Biological Research in Space may contribute to the advancement of the new Biology, in particular to the branch known as "Evo-Devo". On the other hand, as much as the Space Adventure will continue involving human beings as the main actors in the play, long-term multi-generation experiments using a fast reproducing species, such as Drosophila melanogaster, capable of producing more than 300 generations in 15 years, the useful life foreseen for ISS, will be important. Among other useful information, they will help in detecting the possible changes that a biological species may undergo in such an environment, preventing the uncontrolled occurrence of irreversible deleterious effects with catastrophic consequences on the living beings participating in this endeavour.

Evaluation of differential gene expression during behavioral development in the honeybee using microarrays and northern blots

BACKGROUND

The honeybee (Apis mellifera) has been used with great success in a variety of behavioral studies. The lack of genomic tools in this species has, however, hampered efforts to provide genome-based explanations for behavioral data. We have combined the power of DNA arrays and the availability of distinct behavioral stages in honeybees to explore the dynamics of gene expression during adult development in this insect. In addition, we used caffeine treatment, a procedure that accelerates learning abilities in honeybees, to examine changes in gene expression underlying drug-induced behavioral modifications.

RESULTS

Spotted microarrays containing several thousand cDNAs were interrogated with RNAs extracted from newly emerged worker bees, experienced foragers and caffeine-treated bees. Thirty-six differentially expressed cDNAs were verified by northern blot hybridization and characterized in silico by sequencing and database searches. Experienced foragers overexpressed royal jelly proteins, a putative imaginal disc growth factor, a transcriptional regulator (Stck) and several enzymes, including alpha-glucosidases, aminopeptidases and glucose dehydrogenase. Naive workers showed increased expression of members of the SPARC and lectin families, heat-shock cognate proteins and several proteins related to RNA translation and mitochondrial function. A number of novel genes overexpressed in both naive and experienced bees, and genes induced by caffeine, have also been identified.

CONCLUSIONS

We have shown the usefulness of this transcriptome-based approach for gene discovery, in particular in the context of the efficacy of drug treatment, in a model organism in which routine genetic techniques cannot be applied easily.