For the 1st time, all Genes Activated in 1st few days of a Fertilized Human Egg Mapped

Mitosis, stage four (stock image). At the start of an individual’s life there is a single fertilized egg cell. One day after fertilization there are two cells, after two days four, after three days eight and so on, until there are billions of cells at birth. The order in which our genes are activated after fertilization has remained one of the last uncharted territories of human development. Credit: © Tatiana Shepeleva / Fotolia

The fertilized egg gene mapping provides an in-depth understanding of early embryonic development in humans – and scientists now hope that the results will help finding for example new therapies against infertility and genetic disease. There are ~23,000 human genes in total. In the current study, scientists found that only 32 of these genes are switched on 2 days after fertilization, and by day 3 there are 129 activated genes. 7 of the genes found and characterized had not been discovered previously.

“These genes are the ‘ignition key’ that is needed to turn on human embryonic development. It is like dropping a stone into water and then watching the waves spread across the surface,” says principal investigator Juha Kere, professor at the Department of Bio-sciences and Nutrition at Karolinska Institutet and also affiliated to the SciLifeLab facility.

The researchers had to develop a new way of analyzing the results in order to find the new genes. Most genes code for proteins but there are a number of repeated DNA sequences that are often considered to be so-called ‘junk DNA’, but are in fact important in regulating gene expression. They show the newly identified genes can interact with the ‘junk DNA’, and that this is essential to the start of development.

“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,” says Outi Hovatta, professor at Karolinska Institutet’s Department of Clinical Science, Intervention and Technology, and a senior author. http://ki.se/en/news/study-reveals-the-genetic-start-up-of-a-human-embryo