What is epigenetics?

Answers derived from an interview with Damon Lisch, Associate Professor of Botany & Plant Pathology.

What is epigenetics, and how is it inherited?

Epigenetics — where the prefix “epi” means “above” or “on” — means on top of genetics. When we study genetics in school, we mainly talk about the DNA base codes A, T, G and C. Epigenetics, however, is the study of the physical changes in how this DNA is coiled or chemically modified.

To fit within a cell, the long strands of DNA are wound around proteins called histones. Chemical tags, like an acetyl or methyl group, can be added by the cell to those histones and act as an on-or-off switch to genes. 

Epigenetic changes are heritable from every body cell to its daughters. Just as DNA is copied and passed on to daughter cells in mitosis, the epigenetic markers are also carried on to all future cells that are derived from the original. However, further epigenetic changes may occur in those daughter cells after division, making them distinct from the parent cell.

While every non-reproductive cell of an organism is genetically the same, they are able to take on different roles because of epigenetics. This is why a tree trunk appears different from leaves — they have the same DNA, but different genes are expressed and in different amounts.

When reproductive cells are formed, they go through a reprogramming phase where most epigenetic markers are erased. This way, offspring develop a different epigenome than their parents.  

How is the epigenome modified by humans, and are those modifications considered GMO?

Epigenome editing, in theory, has a lot of promise. The ability to turn genes on or off in different parts of an organism could have major impacts on health therapies and new crop varieties. This field is new and evolving quickly, and it is currently possible to use CRISPR-Cas9 systems and methyl transferases — proteins that move methyl groups on and off of histones or DNA — to artificially silence, or turn off, specific genes. 

Making reliably transmitted changes is a challenge because of reproductive cell reprogramming, during which the epigenome is largely reset. Introduced epigenetic changes are unlikely to be inherited in offspring, and those that are may be unstable and unpredictable. Eventually, scientists may be able to make epigenetic changes that are more reliable and could enhance the flexibility of gene expression.

While epigenetic engineering does not introduce DNA from other species into an organism, it is not yet known if it would be labeled and regulated as a genetically modified organism (GMO).