What do you mean, "epigenetic"?

Abstract

Interest in the field of epigenetics has increased rapidly over the last decade, with the term becoming more identifiable in biomedical research, scientific fields outside of the molecular sciences, such as ecology and physiology, and even mainstream culture. It has become increasingly clear, however, that different investigators ascribe different definitions to the term. Some employ epigenetics to explain changes in gene expression, others use it to refer to transgenerational effects and/or inherited expression states. This disagreement on a clear definition has made communication difficult, synthesis of epigenetic research across fields nearly impossible, and has in many ways biased methodologies and interpretations. This article discusses the history behind the multitude of definitions that have been employed since the conception of epigenetics, analyzes the components of these definitions, and offers solutions for clarifying the field and mitigating the problems that have arisen due to these definitional ambiguities.

Keywords: epigenetic inheritance; gene expression; maternal effects; transgenerational.

Figure 1

Imagine the expression of gene A is dependent on the expression of gene B (a transcription factor or si/piRNA perhaps). If we see variable expression in A, but no change in the sequence of gene A, we may conclude that this provides evidence for the expression of A being sequence independent and a product of epigenetics, as shown below. However, it is possible that sequence changes have occurred in gene B, producing transcriptional changes in A. This would make the expression of A dependent on the primary sequence of gene B but not the sequence of A itself. This makes the task of proving sequence independence difficult because you cannot simply look for sequence changes in the coding region of the gene in question, but must also be sure expressional changes aren’t due to mutations elsewhere on the chromosome or other places in the genome.