Epigenetic diseases

Author: B. Horsthemke
Submitted: Tuesday 14th of September 2010 05:08:18 PM
Submitted by: egf
Educational levels: expert, qc3



One of the most fascinating processes in biology is the development of a fertilized egg into a complete organism. More than 2,000 years ago, the Greek philosopher Aristotle proposed that development proceeds through a set of new structures that are not present in the fertilized egg. He called this process "epigenesis". In the middle ages, scientists rejected this idea and believed that adult structures are preformed in the sperm. By careful experiments, however, Harvey (1651) und Wolff (1759 and 1768/69) could demonstrate that the preformation theory was wrong and that the epigenetic theory was right. Nevertheless, the mechanisms underlying the epigenetic process remained obscure for a very long time. In the 1940s, the British biologist Conrad Hal Waddington introduced genetics into embryology and founded the field of epigenetics. He coined the word "epigenetics" by fusing the words "epigenesis" and "genetics" and defined the new field as "the branch of biology that studies the causal interactions between genes and their products which bring the phenotype into being". He discovered that development is characterized by canalisation and plasticity, which are two sides of the same coin. Canalisation refers to the fact that minor changes in the genome or environment do not change the developmental trajectory of an organism, i.e. development is robust. Plasticity refers to the fact that at certain susceptible periods, the developmental trajectory can be changed by the environment to produce a different outcome, i.e. a genotype can have two or more phenotypes. Studies in the past twenty years have revealed the molecular mechanisms underlying canalisation and plasticity. These studies have shown that development proceeds through epigenetic states that are mitotically stable, but potentially reversible. At present, we recognize four epigenetic inheritance systems that account for this metastability: Structural inheritance, autoregulatory feed back loops, RNA-based inheritance, and chromatin marks.


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B. Horsthemke. Epigenetic diseases. EUROGENE portal. September 2010. online: http://eurogene.open.ac.uk/content/epigenetic-diseases



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