Eggs created from human skin cells and then fertilised

Egg cells have been created from human skin cell DNA, which have then been fertilised with sperm to create embryos.

Human embryos containing DNA from skin cells have been created by researchers at Oregon Health and Science University (OHSU), Portland, Oregon. The embryos were created by removing the nucleus of an egg cell and replacing it with the nucleus of a skin cell, as described in the publication in Nature Communications. The chromosome pairs were encouraged to separate and one of each pair was removed. These eggs were then fertilised with sperm to create an embryo.

'We know it works in nature, but we don't fully understand how chromosomes pair and separate correctly. Now we're trying to recapitulate that in vitro, and it's incredibly challenging,' said Paula Amato, professor of obstetrics and gynaecology at OHSU and co-corresponding author of the study.

Somatic cell nuclear transfer was pioneered as a technique for cloning in the 1990s, resulting in the creation of Dolly the sheep (see BioNews 1131). However, the embryos created contained 23 pairs of chromosomes from the donor nucleus, rather than one chromosome in each pair being derived from the sperm cell. The generation of human egg cells with somatic cell DNA and 23 single chromosomes, rather than 23 pairs, is novel. This requires an extra step where one chromosome from each pair is removed, leaving the remaining halves of the pair to be matched with the corresponding chromosomes from the sperm cell during fertilisation.

This proved challenging, with many modified eggs having the wrong number or combination of chromosomes, meaning that a viable embryo could not be created. In the study, 82 eggs were created, with nine percent progressing to blastocyst stage.

'The bottom line is that we're kind of halfway there, but still not exactly where we need to be,' said Professor Shoukhrat Mitalipov, director of the Centre for Embryonic Cell and Gene Therapy at OHSU and co-corresponding author of the study. However, he added, 'Eventually, I think that's where the future will go because there are more and more patients that cannot have children.'

While the success rate is low, this work shows it is possible to create egg cells containing 23 chromosomes using somatic cell DNA. This could allow for women who do not have viable eggs, either through age or other reasons such as cancer treatments, as well as same-sex couples, to become genetic parents. However, as the researchers themselves admit, perfecting the technique and establishing its safety in patients will be challenging next steps.

Professor Richard Anderson, chair of clinical reproductive science at the University of Edinburgh and trustee of PET (the Progress Educational Trust) said: 'The ability to generate new eggs would be a major advance, and this study shows that the genetic material from skin cells can be used to generate an egg-like cell with the right number of chromosomes to be fertilised and develop into an early embryo. There will be very important safety concerns, but this study is a step towards helping many women have their own genetic children.'