Chapter 1 - Basics of epigenetics: It is more than simple changes in sequence that govern gene expression

Abstract

It is a widely accepted fact that distinction between species is defined not only by the ensemble of its genes but also more critically by how these genes are regulated such that the expression profiles change over space and time. Two major factors that determine gene expression and, in fact, a particular state of a functional cell, include genetics, the study of heritable changes in the nucleotide sequences, and epigenetics, the study of mitotically and/or meiotically heritable alterations in gene expression that are not associated with changes in the underlying DNA sequences. Here, we provide an overview about the major epigenetic mechanisms including DNA methylation, histone posttranslational modifications, chromatin modifications, and noncoding RNAs (including miRNAs and lncRNAs) that govern changes in gene expression that are actually dependent on the environment and not on the underlying gene sequence. These mechanisms are potentially reversible and play crucial roles in regulating normal growth and differentiation. Alteration in the epigenetic marks have often been linked with different disease processes; and several attempts have been made to use these epigenetic modifications as a biomarker for the identification of individuals at risk and/or suffering from a disease condition using minimally invasive techniques. Additionally, the reversible nature of these epigenetic marks offers an attractive target for therapy, and hence, several drugs that target epigenetic factors and/or the linked pathways are currently being developed and/or tested in clinical trials. These topics have been extensively discussed through the length of this chapter.