Human activities impact the natural environment in many ways, including by modifying landscape and seascape, increasing pollution, and contributing to global warming. Stress is a non-specific 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 behavioural 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 in the genome. In this project, the fruitfly Drosophila melanogaster (Dm) will be used as model species for evaluating the effects of environmental stress factors on TEs expression and mobility. Dm is a particularly suitable model as it combines genetic amenability, low cost and compatible culture conditions with large-scale screenings. Beyond temperature, a type of environmental stressor 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 clarify how environmental stressors, to which organisms including humans can be exposed in the natural environment, can modulate TEs expression. TEs can have a double effect. On one hand, they can induce deleterious mutations causing dysfunction, disease and even lethality in individuals. It has been shown that various forms of cancer are associated with the presence of TEs within sensitive genes (38 for a review). 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 at transgenerational level. Gonads will be particularly analyzed 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.
This research also has ecological relevance since 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 behavioral 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 understanding 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 ([39] for a discussion). In order to explain these apparently Lamarckian phenomena, the concepts of canalization and assimilation were proposed [40]. 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 [41]. 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 an insertional mechanism of mutagenesis. If these effects and the modulation of the stress response will be demonstrated in different populations, the increase in genetic variability due to TEs mobilization might represent a general phenomenon occurring in response to environmental changes.