Epigenetics: of mice and men and women.
This is the second of two posts on epigenetics. In the first I was critical of using epigenetics to explain the transgenerational transmission of trauma. In this post I am less critical, but the epigenetics of trauma remains a research project in its early stages. The ACE test (adverse childhood experience), available now, is a better use of epigenetics.
The epigenetic scaffold
It used to be thought that the chemical scaffold that surrounded the DNA double-helix was unimportant. Today scientists recognize its importance. This scaffold is called the epigenome (epi from the Greek for above), and is composed of proteins and other chemicals. The scaffold chemically tells a gene whether to turn on or off. A gene that is turned off is like no gene at all. Experience in the world effects the epigenome, which means that the experience of trauma, or more accurately susceptibility to trauma, can be genetically transmitted in the same way other traits, such as hair color, are genetically transmitted.
Two mechanisms are particularly important for gene silencing. DNA methylation and histone modification. DNA methylation is the best-known example of a mitotically (referring to cell division) heritable epigenetic modification. (Ennis, loc 354). Unlike DNA methylation, most scientists thought that histone modification patterns weren’t copied directly to the new chromosomes produced during mitosis (cell division). However, a study by Susan Strome showed that some of the original strand’s modified histones are passed to the newly forming strand during DNA replication (Ennis, loc 354, 422). Other studies have confirmed this result.
It seems clear that epigenetic changes brought about by experiences such as trauma may be transmitted to subsequent generation during the process of reproduction. Whatever else is discovered about the epigenome, it is no longer makes sense to distinguish sharply between nature and nurture. Still, we should not become overenthusiastic. Strome’s study was done with worms; most are done with mice or rats.
