What is Meant by Epigenetics

We use the term epigenetics to denote stable changes in gene expression that are mediated via altered chromatin structure. Increasing evidence implicates epigenetic mechanisms in a wide range of neuropsychiatric phenomena, including depression.
The last 10 years have witnessed explosive advances in our understanding of how the organization of chromatin - the association of DNA with histones and vast numbers of non-histone proteins in cell nuclei - controls the expression of specific genes in all tissues, including brain. Numerous types of histone modifications, chemical changes made to these specialized nuclear proteins, as well as many other types of chemical changes in nuclei, have been shown to mediate alterations in gene expression that occur in diverse tissues in response to environmental stimuli. While many of these histone and other modifications are transient, a subset are long-lived and are believed to contribute importantly to lasting cellular plasticity. Prominent among such regulatory mechanisms are modifications of histones, along with the “writers,” “erasers,” and “readers” of these modifications. Dr. David Allis is a leading authority in this field, and has contributed to the notion that a histone code is a central determinant of a gene’s activity and its potential to be activated or repressed in response to a subsequent stimulus.
Another use of the term epigenetics is to denote mechanisms by which aspects of an individual’s experience can be passed onto his or her offspring without altering DNA sequence per se. Such trans-generational transmission of traits through epigenetics remains highly controversial.

See also:

About Depression and Its Treatments: Basics of Brain Function:
Epigenetic Mechanisms of Depression