Human egg fertilization triggers a flow of genetic activity. After 1 day, the single cell becomes two, after 2 days there are four cells, after 3 days there are eight, and so it continues. Now, for the first time, scientists at the famous Karolinska Instiutet in Sweden have mapped the genetic activity that accompanies this early stage of embryo growth.
The international study found novel insights into the regulation of early embryonic development in humans. The study is the first to map all the genes that are activated in the first few days of embryo development from the point of fertilization; a discovery the researchers said was akin to finding the "ignition key" that switches on human development.
While there are approximately 23,000 human genes, the order in which genes are activated following fertilization has been a mystery until now. The team found that on the second day after fertilization only 32 of the 23,000 human genes were switched on. By the third day, the number of active genes rises to 129. Seven of these active genes had not been previously identified.
Most genes carry the instructions for making proteins. There are a number of repeated sequences in our DNA that were initially thought to be ‘junk’ DNA but were later discovered to be regulating the genes that code for proteins.
The new genes the researchers found appear to interact with the so-called ‘junk’ DNA, and this interaction is essential for triggering early embryo development. This could have far reaching consequences for future research in reprogramming cells into so-called pluripotent stem cells, which have the potential to treat a range of diseases, as well as in the treatment of infertility.
New research has also shown that it is not the aging of the eggs themselves but aging of their environment that appears to reduce older women's chances of conceiving through IVF (in vitro fertilization). The researchers found that retrieving eggs from the ovaries earlier than in conventional IVF led to increased production of good quality embryos and higher success rates.