For the first time, scientists were able to see some of the earliest genetic mutations in human development.
Using whole genome sequencing, they wound back time on cell samples from adults and revealed what took place in the genome when they were still microscopic embryos.
It turns out, our first two cells contribute to our development in very different ways.
The mutations appear in two forms: the hereditary ones we receive them from our parents and can be found in almost every cell of the body, and the acquired (or somatic) mutations that can appear at any stage of a person’s life, including the first days when the embryo is just starting to split into multiple cells.
Somatic mutations are not always causing problems, but sometimes they can sometimes lead to cancer and other diseases, and also they do not live in every cell.
So far, our understanding of somatic mutations that appear in the earliest stages of life was not exactly precise, because we were not able to observe them in real time. But now, researchers have discovered a way to follow these mutations from their first appearance.
To do this, the research team analyzed samples of blood and tissue from 279 people with breast cancer, which allowed them to test whether the mutations were present in both normal blood and tissue, as well as in surgically removed tumour samples.
Because this type of cancer is developed from a single cell, the somatic mutation would either be present in every tumor cell or nowhere, which gives an indication to its possible origins.
By monitoring and comparing the spread of different mutations in different tissue ssamples, scientists have confirmed the existence of 163 mutations that have appeared within the first few cell divisions of the persons embryonic development.
Once identified, the researchers used mutations from the first, second and third divisions of the fertilised egg to calculate which proportion of adult cells resulted from each of the first two cells in the embryo. They found that these first two cells contribute differently to the whole body. One cell gives rise to about 70 % of the adult body tissues.
Basically, the mutations are “archeological traces” of embryonic development in our other adult tissues, so if you find a way to find and interpret them, we can better understand the human embryology.