Human egg fertilization sparks a cascade 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 have mapped the genetic activity that accompanies this early stage of embryo growth.

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The study shows that on the second day after fertilization, only 32 of the 23,000 human genes are switched on.

The international study, led by the Karolinska Institutet in Sweden, is published in the journal Nature Communications.

"Our results provide novel insights into the regulation of early embryonic development in humans," reports senior author Outi Hovatta, a professor of clinical science, intervention and technology.

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 that is akin to finding the "ignition key" that switches on human development, according to one of the researchers.

While there are approximately 23,000 human genes, the order in which genes are activated following fertilization has been a mystery until now.

Prof. Hovatta and colleagues hope the results will open a number of research avenues, such as discovering new treatments for infertility and other diseases.

Researchers identify new genes activated shortly after fertilization

The team found that on the second day after fertilization, only 32 of the 23,000 human genes are 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. Prof. Hovatta explains how this might be useful for future research:

"We identified novel factors that might be used in reprogramming cells into so-called pluripotent stem cells for possible treatment of a range of diseases, and potentially also in the treatment of infertility."

Meanwhile, Medical News Today has learned of a new IVF approach that older women may find more successful. The researchers behind the new development discovered that it is not 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.