Epigenetics Modifications - Introduction

Introduction to Epigenetics Modifications

Epigenetics is the study of heritable traits that do not involve changes to their underlying DNA sequence. Epigenetic signals within the cell modulate particular transcriptional states (epigenetic states) necessary for the cell to "remember" previous stimulus events, including developmental signals and environmental changes (1). The molecular foundation of epigenetic signalling is the remodeling of chromatin, which occurs through a combination of (a) post-translational modification of amino acids in histone proteins, and (b) DNA methylation. The interplay between chromatin remodeling and other signaling molecules such as transcription factors and non-coding RNA controls the level and pattern of transcription from chromatin necessary to generate a given epigenetic state in the cell (2). The classic examples of epigenetic processes are cellular differentiation and maintenance of cell identity through multiple cell divisions over the lifetime of a multi-cellular organism (3).

Epigenetic signals can be divided into two main categories, cis- and trans-. Trans-epigenetic states are primarily self-propagating transcriptional states maintained via feedback loops and transcription factor (TF) networks (4). For example, if an external stimulus causes a TF to activate its own transcription, the result is a (trans) epigenetic state that becomes self-sustaining when the stimulus is removed, and continues after cell division. Small RNAs (sRNAs) also sometimes function as trans-epigenetic signals (5). Trans-epigenetic states are often found in prokaryotes and single-celled eukaryotes, where they support cellular memory.

Fig 1 : Modification : dC Analogs