Stress is an nonspecific response of the organisms to biotic and abiotic environmental changes such as temperature, climate factors and chemical compounds. Stress conditions induce in animals a complex physiological response occurring at neuroendocrine, physiological and behavioral levels that may also have consequences at population level. Adverse environmental conditions may cause long-term effects on genome stability, leading to heritable alterations in genome structure. Over the last decade, it has become evident that some stress conditions and other environmental stimuli can induce the expression and the activity of transposable elements (TEs). As their name suggests, TEs are DNA repetitive sequences having the capability to move from one location to another within the genome. In this project, the fruit fly Drosophila melanogaster (Dm) and the zebrafish Danio rerio (Dr) will be used as model species for evaluating the effects of environmental stress factors on TEs activity. The two species are particularly suitable models as they combine genetic amenability, low cost and compatible culture conditions with large-scale screenings. Beyond temperature, several types of environmental stressors due to human activity will be tested. Results will give insights on the capability of the environmental stress to act as an evolutionary force triggering genetic variability and animal adaptation. Data will also help to appreciate the effects of TEs expression on human health.
The project will contribute to identify how environmental stressors, to which organisms including humans can be exposed in the natural environment, can modulate TEs expression in both invertebrates and vertebrates. TEs can have a double effect. On one hand, they can induce deleterious mutations causing dysfunction, disease and even lethality in individuals. On the other hand, TEs can increase gene variability, making populations more able to respond adaptively to environmental changes. For this double action, results of our project can have a deep impact in many research fields.
The proposed studies will allow the scientific community to evaluate whether selected chemicals and pollutants have dangerous effects on living organisms that need to be monitored carefully. The effects of stressors will be analyzed at different developmental stages and in different tissues/organs as gonads and brains, to evaluate where and when TEs are more expressed as a result of treatments. Gonads will be particularly analysed to evaluate if also in these organs the stressors can determine an over-expression of TEs, highlighting the possibility of transmitting the induced mutations to the offspring. If a strong TEs modulation will be verified in Dr, this result will represent the cognitive base for future translational studies to humans with potential applications in terms of safety and health.
The study also has ecological relevance since the climate change may significantly affect biodiversity, causing extinction with consequent profound changes in ecosystems. Increasing temperature and other environmental stressors can induce phenotypic variations at morphological, physiological and behavioural level, that might also lead to genetic adaptations. These changes can be properly studied in organisms with short life cycles such as Dm. On the whole, the proposed investigation will contribute to better understand the effects of global warming on species survival, also providing an easy and quick way to infer the adaptive capacities of higher vertebrates, including man.
Finally, the proposed study will make a significant contribution to the advancement of knowledge on the genetic mechanisms of evolution. Various examples of apparently heritable characters acquired during the course of life are known in nature for a discussion). In order to explain these apparently lamarckian phenomena, the concepts of canalization and assimilation was proposed [24]. This hypothesis foresees the existence of pre-existing genetic variation kept hidden by the robustness of the development processes. The developmental pathway can change through the expression of a cryptic genetic variant. This variant can be selected and become heritable by an assimilation process [25]. Evidence that heat shocks induce TEs mobilization in Dm, suggest that the assimilation process is not due to the expression of a cryptic variant, but to the onset of de novo mutations through a mechanism of insertional mutagenesis. If these effects will be confirmed for different stressors and in different organisms, the increase in genetic variability due to TEs mobilization might represent a general phenomenon occurring in response to environmental changes.
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