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Biomedical subjects

F A Lints

Publications and source records attributed to F A Lints.

At least 19 recordsLinked to original sources

Novel and transgenic food crops: overview of scientific versus public perception.

Recombinant DNA technology offers opportunities to develop new products in many different fields, including agriculture and the agro-food area. Transgenic plants with improved agronomic traits currently grow in field trials and a few varieties have already reached the European market. By and large, new technologies raise both concerns and expectations and modern biotechnology is no exception. Indeed, a voluntary moratorium on experiments involving recombinant DNA molecules was called for in 1974. At the present time, although a majority of academic and industrial scientists agree that transgenic food crops pose no risk for the environment or human health, some others believe that certain applications of modern plant biotechnology are hazardous. In particular, deliberate releases of genetically modified plants are regarded as risky. There is also a disparity between expert and lay perception of r-DNA technology applications to food crops, which makes public information a difficult task. This paper aims at exposing these conflicting points of view on the agricultural applications of modern biotechnology. We also propose some recommendations pertaining to public information in Europe. It appears that consensus conferences might be a good approach to stimulate public information and public debate in Europe, although this approach has to be adapted to the cultural context of each country.

Agriculture↗

Scientific and ethical issues of preimplantation diagnosis.

Preimplantation diagnosis (PID) offers couples at high risk of having offspring affected with a genetic disorder the possibility of an early prenatal diagnosis. For many couples this approach will give the opportunity to avoid a selective termination of affected pregnancies. Substantial advances were made in PID since the report, in 1990, of the first birth obtained after PID. Yet, many technical hazards have to be solved for PID to become a standard clinical tool. The very close correlation existing between the forthcoming developments in the fields of PID and human genome mapping will improve the reliability and efficiency of genetic diagnosis. In the near future, the procedure may also become easier and safer. As a consequence, the indications for PID could be extended to other genetic defects, such as multifactorial diseases. They could also be extended to cases with no medical background, such as social gender selection or behavioural traits. In this perspective, it is now time for both the medical and scientific communities to identify the ethical issues related to these potential new indications.

Ethics, Medical↗

Selection for increased longevity in Drosophila melanogaster: reflections on new data.

In recent papers, new data were presented on the late-age reproduction experiment initiated by Luckinbill and Clare in 1981: when early- and late-reproduced lines were compared simultaneously 10 years after the end of the original experiment, differences in the mean life span are observed between the lines. Yet the conditions in which these measurements were done are highly questionable. More fundamentally, using these data, the analysis of the selection process is impossible and conclusions about the determinism of life span are debatable.

Aging↗

Realized heritability of longevity in Drosophila melanogaster.

From the data of an experiment of selection for increased longevity, a realized heritability of longevity was calculated. The low value of this heritability (3.4%) was very close to values observed in other experiments concerning Drosophila melanogaster wild strains. The error variance of the heritability estimator was calculated through the use of orthogonal contrasts. In this way, it was possible to calculate the confidence interval of the realized heritability. The amplitude of this interval was wide although the size of the sample was large. This shows the difficulty of estimating with precision the heritability of longevity from data obtained in selection experiments.

Animals↗

Life-span of Drosophila melanogaster in highly oxygenated atmospheres.

The life-span of Drosophila melanogaster males kept for their entire life in atmospheres of differing O2 concentration (21%, 30%, 40%) was measured. The life-span decreased linearly with the increase in O2 proportion. In order to test the rate of living and the threshold theories of ageing, Drosophila melanogaster males were kept for 15 days in a given atmosphere and from day 16 on in another one. The life-spans observed in these alternate conditions were very close to the values predicted by the rate of living theory and are thus not compatible with the threshold theory.

Animals↗

Hypergravity, aging and longevity in Drosophila melanogaster.

1. Drosophila melanogaster flies have been used in studies of the effect of hypergravity (HG) on aging and longevity. 2. There is no clear longevity decrease with the gravity level up to 4 g and, even at 7 g, flies still live for roughly 40 days. 3. The HG-related changes in fecundity suggest that flies counteract an increased metabolic demand. 4. Viability is barely affected in HG. 5. These results show that flies remain able to lay viable eggs and to live for a fairly long life, even at high HG levels. 6. The study of three behavioral traits affected by aging (climbing activity, pattern of movement, spontaneous locomotor activity) suggests that flies age faster in HG, while no HG effect is clearly detected at young age. 7. These results are observed at HG levels where longevity is not yet affected. 8. Results are discussed in relation with Pearl's rate of living theory (1928).

Aging↗

Selection for increased longevity in Drosophila melanogaster: a new interpretation.

The study of the genetic determination of longevity in Drosophila melanogaster has made use of the technique of late-age reproduction. At low larval density, that indirect selection showed no effect. At high larval density, however, increased mean life-span in lines reproduced at late age was observed. When these last data are examined as a function of the number of days after the beginning of the experiment, instead of as a function of generations, the difference in life-span between early and late lines at high larval density disappears. The erratic evolutions of mean longevities in all the experiments here described may be attributed to unexplained variations in life-span previously observed in a 4-year experiment. Considering the time lag between the measurement of a given generation in early and late lines, the experiments of reproduction at late age cannot demonstrate the genetic determinism of longevity.

Aging↗

Hypergravity and aging in Drosophila melanogaster. 4. Climbing activity.

Drosophila melanogaster flies climb up the sides of their vial after having been submitted to a mechanical stimulation; that ability is impaired at older ages. The climbing activity (CLI) of flies kept at various gravity levels (1, 3 and 5 g) has been measured throughout life, in cross-sectional studies. Hypergravity had no effect on CLI at young age, but older flies kept in hypergravity displayed lower scores than flies kept at 1 g. Results are discussed in relation with the hypothesis of increased aging rate in hypergravity.

Aging↗

Hypergravity and aging in Drosophila melanogaster. 5. Patterns of movement.

The paths of young, middle-aged and old Drosophila melanogaster flies, kept at various gravity levels (1-5 g) throughout life, have been recorded in a cross-sectional study. Aging flies exhibit more sinuous paths and do not move as far away from their release point as younger ones. These age-related changes in the patterns of movement are expressed at younger ages in flies submitted to hypergravity. As for the climbing activity experiment, the patterns of movement do not clearly vary with the gravity level at young age. Results are discussed in relation to the hypothesis of increased aging rate in hypergravity.

Aging↗

Hypergravity and aging in Drosophila melanogaster. 6. Spontaneous locomotor activity.

The spontaneous locomotor activity (SLA) of Drosophila melanogaster flies kept at various gravity levels (1-5 g) was recorded in both longitudinal and cross-sectional experiments. No gravity level effect could be detected in the longitudinal one, probably because these flies were allowed (for technical reasons) to rest at 1 g for 15% of their life. By contrast, flies kept at 5 g in the cross-sectional experiment had lower SLA scores at middle and old age than both 1 and 3 g-kept flies. The results of this series of experiments on hypergravity (HG) effects on three forms of locomotor activity (climbing activity, patterns of movement and SLA) allow to conclude that aging is accelerated in HG, even if no longevity decrease could be detected in the 1-4 g range.

Aging↗

Unexplained variations in life span of the Oregon-R strain of Drosophila melanogaster over a four-year period.

The life span of samples of the Oregon-R strain of Drosophila melanogaster was observed, every fourth week, during a four-year period. Large variations, most probably non-random, were observed at both 25 and 21 degrees C. The possible causes of these variations have been searched for, yet no definite conclusion can be reached. The implications of these results for Drosaphila quantitative genetic research are stressed.

Animals↗

The rate of living theory revisited.

A rereading of The Rate of Living [Pearl, University of London Press, London 1928] shows that Pearl's thoughts about the meaning of inheritance and heredity, about the relations of between and within populations measurements and about the ways in which life span should be measured are unclear. New ways in which the theory should, eventually, be tested are suggested and the genetic implications of these suggested experimental ways are given. A review is made, mainly in insects, accessorily in rodents, of the different manners in which the theory has been essayed, namely by relating life span with temperature, rate of energy expenditure, growth rate and activity. It is concluded that the theory rests on a weak theoretical basis and even on a series of highly nonplausible assumptions and that, furthermore, the evidence experimentally accumulated is, with a few odd exceptions, not in favor of the theory.

Aging↗

Hypergravity and ageing in Drosophila melanogaster. 1. Fecundity.

In Drosophila melanogaster daily fecundity has been recorded throughout life of flies kept at various gravity levels (1-5 g). Hypergravity (HG) did not decrease total fecundity but modified its expression during life. The 1 g group could be opposed to the various HG groups, i.e. a clear regression of the various fecundity items on the HG level could not be disclosed. Results are discussed in relation with Pearl's rate of living theory.

Aging↗

Hypergravity and ageing in Drosophila melanogaster. 2. Longevity.

Longevity of Drosophila melanogaster flies was observed at various gravity levels in three different breeding conditions of decreasing quality. A slight longevity decrease was observed in the 1-4 g range of the two best conditions. In the third one, a large decrease was observed in all hypergravity groups. Longevity decreased at 5 g in the first two groups (no data collected for the third one). Results are discussed in relation with Pearl's rate-of-living theory.

Aging↗

Hypergravity and ageing in Drosophila melanogaster. 3. Viability.

The viability of Drosophila melanogaster was measured in three conditions: (1) of eggs from parents living at different gravity levels (1-5 g), developed at 1 g; (2) of eggs from parents living at 1 g, developed at different gravity levels, and (3) of eggs developed at the gravity at which their parents were kept. Hypergravity (HG) decreased viability to a low extent in all three cases (75% of emergence in the worst case). The effects of keeping parent flies in HG and of growing their offspring in HG were not cumulative. The results are discussed in relation with Pearl's rate of living theory.

Aging↗

Reproductive fitness and longevity in Drosophila melanogaster.

It has been suggested that senescence could have evolved by selection of genes with beneficial effects early in life and detrimental ones later in life (pleiotropy theory of the evolution of senescence). To test that theory, the egg production of 322 females of the Oregon strain of Drosophila melanogaster was recorded daily throughout their life. At the individual level, no relation could be detected between early components of fitness and longevity. For the time being it appears that there are no unequivocal reasons to accept the pleiotropy theory of the evolution of senescence.

Aging↗

Developmental temperature and life span in Drosophila melanogaster. I. Constant developmental temperature: evidence for physiological adaptation in a wide temperature range.

The concept of an inverse relationship between life span of adult Drosophila and their developmental temperature is probably the result of an unwarranted generalization. Rather, in a wild-type laboratory strain the present study revealed a plateau phase in this relationship between 16 and 29 degrees C in which life span of both male and female flies was roughly independent of developmental temperature. Below and above this range, life span dropped drastically, development being impossible below 12 and above 32.5 degrees C. Simultaneous study of growth characteristics showed that the plateau phase corresponded to a 'physiological' range of developmental temperature, development being apparently disturbed outside that range. Within that physiological range, the growth rate of the flies varied varied 2-fold, while life span remained constant corroborating our previous conclusion that growth rate per se does not determine life span.

Adaptation, Physiological↗

Developmental temperature and life span in Drosophila melanogaster. II. Oscillating temperature.

Alternating developmental temperature within the viable range 13-33 degrees C, with increasing amplitude around a mean value of 23 degrees C but constant period (2 days, a 1 day/1 day rhythm), resulted in increased duration of development, decreased body weight and decreased growth rate of both male and female flies. Life span of female flies also decreased with increasing amplitude of temperature of oscillation but that of males increased (compared to that at the mean temperature) at moderate temperature amplitude. Variation of the period of oscillation (from a rhythm of 6 h/6 h up to 2 days/2 days) with constant amplitude (23 +/- 5 degrees C), on the other hand, did not affect either duration of development or body weight of the flies. However, life span of the females only was unaffected but that of males was increased (above that at mean constant temperature 23 degrees C) at the fast oscillation patterns (6 h/6 h and 1 day/1 day). Finally, life span of both sexes was positively correlated with growth rate in the constant period/varying amplitude case, whereas in previous studies variation of growth rate in the same range by other means showed a biphasic or an invariant pattern of life span dependence on growth rate. These results are in agreement with the hypothesis of epigenetic influence on life span by alternating developmental temperature and corroborate the previous conclusion that growth rate per se does not determine life span.

Animals↗