The effects of X-irradiation on the longevity of triploid and diploid female Drosophila melanogaster

The essential mechanisms of aging: Irreparable damage accumulation of biochemical side-reactions

Explanations on aging mechanisms have now become unexpectedly complicated. However, it is gradually accepted that 'senescence is a collective consequence of both inheritance and environment'. Based on the achievements of biological and medical research in related fields, we pinpoint in this review that although aging is mainly considered a physiological (non-pathological) process, the biochemical structure of aged organisms is deranged, or 'sick' at the molecular level. The free radical/glycation induced carbonyl stress, the key culprit to form crosslinks, has been identified to cause stable cyclic conjugates of mainly protein-based aggregates implying entropy increase (the Second Law of Thermodynamics) during aging. When combining such key aging processes with age pigment biochemistry, a general picture of aging process can be figured out, as the main clues and results are available. In this review we also propose for the first time that by focusing on 'process' rather than on 'causes' (damages), we can then get a clear view of aging mechanisms. Through rational thinking and critical analysis, we conclude that the accumulation of irreparable damages and alternations caused by spontaneous biological side-reactions seems to be the essential and profound nature of higher animals' aging mechanisms.

Transposable elements as a factor in the aging of Drosophila melanogaster

We have considered the hypothesis that transposable elements may contribute to the aging process through somatic mutation. We have presented evidence to suggest that at least two elements, Copia and 412, are capable of somatic activity in adult Drosophila tissue. A strain harboring a third transposable element, P, was produced that showed eye color mosaicism and reversion to wild phenotype (red eyes) as a result of somatic and germ line transposition. A high-fat diet, known to accelerate aging, increased the frequency of eye color mosaicism and red eyes. We induced life span shortening by artificially activating somatic transposition of P elements, and the extent of reduction in life span was similar in both sexes. These data are consistent with the notion that some aspects of the age phenotype may be caused by mutational activity of transposable elements in somatic tissues. The hypothesis is readily tested in other organisms, including humans. It offers new dimensions in the understanding and management of age-associated changes.

DNA, mutations and aging

Genetic instability is widely thought to be involved in the process of aging. Evolutionary theory suggests that aging may well result from stochastic damage to DNA. However, studies of the dynamics of accumulation of simple somatic mutations have shown that such a mechanism cannot readily account for experimental observations. A more complex mutational theory of aging is emerging which allows for interaction between mutations, for damage to epigenetic controls on gene expression, and for interaction of (epi)genetic changes with other possible molecular events contributing to aging.

Accelerated aging of the insect Drosophila melanogaster by gamma irradiations of pupae

The purpose of this study was to induce accelerated aging in the fly Drosophila melanogaster (Diptera) using free radicals, and to distinguish aging from radiation syndrome. After irradiation of 12 to 24-hour-old pupae with does of 500-2500 rad, very similar fly emergence rates were observed in control and treated populations. The life span was shortened and dose-related in mixed populations and in both virgin and mated male and female populations. Males were more radiosensitive than females. In the 500-2500 rad dose range, all the populations tested were fertile after irradiation. Young treated as pupae and control adults both displayed similar mating ability and negative geotactic responses. Their response levels decreased with time, but the decline was faster and dose-related in the treated animals. This study demonstrates that irradiation of 12 to 24-hour-old pupae with doses of 500-2500 rad induces accelerated aging, without causing serious biological damage. For example, after an irradiation with 1750 rad, the "lethal time" (LT) 50 dropped by about 30%.

Effects of U.V. radiation on the lifespan of the rotifer Asplanchna brightwelli

Groups of rotifers of the species Asplanchna brightwelli were exposed to U.V. irradiation at dosages ranging from 50 to 4800 J/m2. The lifespan of the rotifers was significantly reduced by exposure to U.V. in the range of 200 to 4800 J/m2. A logarithmic decline in lifespan was seen as the U.V. dose increased. Rotifers were most sensitive to U.V. exposure during the prereproductive stage at the beginning of their lifecycle. Exposure of rotifers to visible light following U.V. radiation provided no evidence that photoreactivation could influence lifespan in this species.