Chapter 1 - Introduction to Epigenetics

Abstract

Epigenetic modifications are defined as stable and heritable alterations in gene expression and cellular function without changes to the original DNA sequence. Since 1942, when C.H. Waddington first used the term epigenetics to depict a phenomenon that genetics could not explain, the knowledge in this field has soared and evolved into a branch of science with well-understood molecular mechanisms. The well-recognized epigenetic mechanisms comprise DNA methylation, histone modification, and noncoding RNAs (ncRNAs). DNA methylation is a genetically programmed modification that involves the addition of a methyl group onto the position 5′ of a pyrimidine ring on cytosines (5mC). It is referred to as the “fifth base” and mediated by DNA methyltransferases (DNMTs). In addition, posttranslational modifications on the tails of core histones can switch a favorable or unfavorable chromatin status for gene transcription. The roles of ncRNAs in regulation of gene expression are sophisticated. However, it is believed that ncRNAs are important epigenetic regulators in cell differentiation, especially microRNAs (miRNAs) and long noncoding RNAs (lncRNAs). With the advancement of technology, a growing body of evidence indicated the role of epigenetics in development and disease. In this chapter, we make an introduction to the function and mediation of the three main epigenetic mechanisms and their association with skin diseases.