Epigenetic effects on the embryo as a result of periconceptional environment and assisted reproduction technology

The early embryonic environment has been shown to be remarkably influential on the developing organism, despite the relative brevity of this developmental stage. The cells of the zygote and cleavage-stage embryo hold the potential to form all cell lineages of the embryonic and extra-embryonic tissues, with gradual fate restriction occurring from the time of compaction and blastocyst formation. As such, these cells carry with them the potential to influence the phenotype of all successive cell types as the organism grows, differentiates and ages. The implication is, therefore, that sublethal adverse conditions which alter the developmental trajectory of these cells may have long-term implications for the health and development of the resulting offspring. One confirmed mechanism for the translation of environmental cues to phenotypic outcome is epigenetic modification of the genome to modulate chromatin packaging and gene expression in a cell- and lineage-specific manner. The influence of the periconceptional milieu on the epigenetic profile of the developing embryo has become a popular research focus in the quest to understand the effects of environment, nutrition and assisted reproduction technology on human development and health.The environment to which a developing embryo is exposed can have a significant influence on the long-term health and risk of disease of the resulting offspring. This is because the cells of the early embryo have the potential to form all the cells of the adult body, therefore any adverse environments experienced by these cells can have downstream effects on many tissues or organs. One mechanism through which the environment can impact on the embryo is to alter the way gene expression is controlled. Modifications to the DNA or the way in which it is packaged within the cells can affect whether individual genes are accessible to the proteins required to activate or silence their expression. In some cases, gene expression change can simply result in plasticity in the development of the embryo. In other cases, these genes could be essential for development and so the consequences are more significant. One of the only ways to study the effects of the embryonic environment in human is by retrospective analysis of maternal dietary effects during gestation or indirectly in assisted reproduction populations. Therefore, animal studies in which environmental and nutritional conditions can be controlled with greater accuracy help us to identify specific aspects of the human embryo environment and their influence on long-term development.