Introduction to Epigenetics

Epigenetics is the study of inherited variations in gene expression that do not involve changes to DNA sequences. Over 200 unique cell types in a human adult have a nearly similar genomic sequence. DNA and histones undergo reversible chemical alterations that contribute greatly to cellular variety via dynamic control of global gene expression, in addition to the genomic sequence. Epigenetics is based on chemical modifications of macromolecules rather than alterations to the chromosomal sequence. Epigenetic modifications, such as DNA methylation, chromatin modifications, nucleosome placement, and changes in noncoding RNA profiles, are reversible and fundamental processes in the regulation of gene expression. Alterations in gene activity and neoplastic transformation of cells may result from epigenetic disruptions. Epigenetic alterations occur at an early stage in neoplastic growth, before the corresponding genetic alterations have actually occurred. Researchers in this area will discover information on a wide variety of topics, all grouped together under the explanatory framework of chemical changes that affect gene expression regulation. In this chapter, we provide information on epigenetics, DNA methylation, and histone modifications.