Towards the end of World War II, the Dutch Hunger Winter was the worst of all, causing a higher rate of casualties than one could have imagined. But it was for the living pregnant women in the worst conditions, and most importantly, their situation had a life-altering impact on the newborns. As per later research, women pregnant during the famine gave birth to overweight children more than regular. And this is what researchers term epigenetic inheritance.
The thinking goes like this, – because mothers were starving during the famine, it automatically quieted the gene in the unborn child, capable of the body’s fat burning. When they reached middle age, these children were more prone to higher triglyceride and cholesterol levels. And most often suffered from higher chances of cardiovascular disease, diabetes, obesity, and schizophrenia. Further research did reveal the children had a particular chemical mark or an epigenetic signature – on one of their genes that underwent possible mutations.
What is Epigenetic Inheritance?
For long, researchers had believed that the epigenome of a new embryo had no relation with the past. But certain epigenetic tags do continue passing down from one generation to the next, known as epigenetic inheritance.
The study of epigenetics is about cells controlling gene-specific activities without altering the DNA sequence. It describes factors beyond the genetic code and how modifications get done over DNA, muting certain genes in the next generation.
There are two types of epigenetic modification sentencing the DNAs to adequate change.
In DNA methylation, methyl groups containing three hydrogen atoms and one carbon atom come attached with DNA building blocks. The gene with methyl groups can no longer produce protein and gets turned off or silenced.
Histones are available in the form of structural proteins within the cell nucleus. DNA wraps around histones offering the ultimate shape to the chromosome. The addition or removal of chemical groups (namely acetyl or methyl groups) controls the shape of histone.
The addition of the wrong gene or failure to add the particular histone or gene leads to abnormal genetic activity. These are known as epigenetic errors and are the common cause of genetic disorders. Conditions like degenerative disorders, cancers, and metabolic disorders are all related to wrong gene attachment or gene mutes.
The Study Of Epigenetic Inheritance On Mice
A study in 2013 did highlight the concept of intergenerational trauma associated with scent. Here the team went on with their research over lab mice, blowing acetophenone – the scent of cherry blossom through the cage gap of adult male mice while zapping their foot with electric current simultaneously. The process was on repeat multiple times until the male mice started associating the smell of cherry blossom with pain.
Shortly after such a conditioning event, the male mice were bred with females. And the pups were all jumpy and nervous when exposed to the smell of cherry blossom. The team separated the pups from the birth parents to erase chances that the children were learning to fear the smell of cherry blossom from their parents. And the kids were raised by new mice couples who were never conditioned to such smell.
However, to the surprise, the grand pups of the traumatized males also had heightened sensitivity to the scent. The mice were not sensitive to any smell other than cherry blossom, indicating epigenetic inheritance of that scent.
The research team linked sensitivity towards the cherry blossom scent with epigenetic modifications in the sperm DNA of the traumatized mice. They did find chemical markers on the DNA of a certain gene related to the olfactory bulb between the brain and the nose. This was involved in sensing the smell of the cherry blossom. Also, the pups’ brains were dissected, where a greater number of neurons could detect the cherry blossom scent compared to the normal mice. The second and third generations of conditioned mice were not usually frightened by the scent but had higher sensitivity.
Thus bringing to light how important it is to study epigenetic inheritance. A subtle experience of trauma by one generation can lead to the other generations becoming highly sensitive. Even though the fear is absent, it is the sensitivity and the feeling of perplexity that the later generation has to deal with.