Epigenetics: from the past to the present

ABSTRACT The definition of epigenetics is still under intense debate; however, its concept has evolved since it was originally introduced in 1939 by Conrad Hal Waddington as a way to reconcile antagonistic views between the school of preformationism and the school of epigenesis. The characterization of a large number of phenomena that diverge from the dogmas of classical genetics, and the discovery of the molecular mechanisms through which these phenomena occur, has given rise to a new area of study with important implications for biological sciences. Interactions between the environment and the DNA through modifications on the chromatin are not only responsible for the expression of a normal phenotype, these may be involved in the development of various pathologies. The epigenome, as the bridge between the genome and the phenotype, is no doubt one of the most interesting current ideas in genetics and is so revolutionary that it may change our present notions about inheritance and evolution. In this review, we made a compilation of the most important events in the history of epigenetics, its implications and some perspectives to the future. Abbreviations: DNA: deoxyribonucleic acid; RNA: ribonucleic acid; DNMT: DNA methyltransferase; MBP: methyl-CpG-binding proteins; HAT: histone acetyltransferase; HDAC: histone deacetylase; SAM: S-adenosyl methionine; ncRNA: non-coding RNA; rRNA: ribosomal RNA; miRNA: microRNA; siRNA: small interfering RNA; piRNA: Piwi-interacting RNA; XiRNA: X-inactivation RNA; lncRNA: long non-coding RNA; GR: glucocorticoid receptor; IGF2: insulin-like growth factor II; HPA: hypothalamic–pituitary–adrenal; TSA: trichostatin A; LINE: long interspersed nuclear elements; LOI: loss of genomic imprinting; MAS: McCune–Albright syndrome; AS: Angelman syndrome; PWS: Prader–Willi syndrome; FDA: Food and Drug Administration; AHEAD: International Human Epigenome Project; HEP: Human Epigenome Project; TMG: thiomethyl-β-D-galactoside