Epigenetics and transgenerational effects of toxic stress in the water flea Daphnia magna
Vandegehuchte, M. (2010). Epigenetics and transgenerational effects of toxic stress in the water flea Daphnia magna. PhD Thesis. Ghent University. Faculty of Bioscience Engineering: Ghent. ISBN 9789059893733. x, 196 pp.
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Document type: Dissertation
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| Abstract |
Epigenetics is the study of mitotically or meiotically heritable changes in gene function that occur without a change in the DNA sequence. Epigenetic changes can be triggered by environmental factors and associated changes in gene expression often lead to phenotypic modifications. Epigenetic alterations can sometimes be transferred to subsequent generations, even when the external factor which induced the epigenetic change is no longer present in these generations. From an ecotoxicological point of view, this mechanism could make populations experience the effects of their ancestors’ exposure to a certain concentration of a chemical, with implications for the environmental risk assessment of chemicals. DNA methylation, an important epigenetic mechanism, was detected and quantified in Daphnia magna. This revealed a DNA methylation level of 0.22% to 0.35% for adult daphnids in standard conditions, which is much lower than in humans, but comparable to the level in some invertebrates. In the F1 generation offspring of F0 generation Zn exposed daphnids, a slight but significant decrease in DNA methylation was observed. This demonstrated that environmental conditions can affect DNA methylation in D. magna. However, this effect did not propagate into the next generation (F2). The effect of zinc exposure during one or more generations on gene transcription in daphnids was studied using custom cDNA microarrays. This was done for the exposed daphnids, but also for their non-exposed offspring. In both groups, the transcription of a large number of genes was affected by the zinc exposure. Certain transcription patterns suggested an effect of reduced DNA methylation on gene transcription. A stable transgenerational epigenetic effect on gene transcription, however, was not observed. To investigate whether DNA methylation as epigenetic mark in D. magna is affected by exposure to substances known to affect DNA methylation in mammals, daphnids were exposed to five different chemicals. Vinclozolin and 5-azacytidine were shown to induce DNA hypomethylation in the first exposed generation (F0). Only with 5-azacytidine was this effect transferred to the two subsequent non-exposed generations, coinciding with a significantly reduced juvenile growth. These results demonstrate the possibility of transgenerational inheritance of environment-induced epigenetic effects in non-exposed subsequent generations of D. magna. |
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