Scientists in Britain have snipped a "master gene" out of human embryos in an experiment that could lead to better fertility treatments and galvanise stem cell medicine.
This latest experiment, led by researchers at London's Francis Crick Institute, is the first in which scientists used genome-editing technology to investigate the function of a particular gene in human embryos, according to an institute release.
After an egg is fertilised, it divides for around seven days until some of the cells cluster together to form a blastocyst, which goes on to become the embryo, while other cells will go on to form the placenta.
The research found fewer than a fifth of the test embryos reached the blastocyst stage without Oct4. The work suggests that a protein called OCT4 has additional roles in human embryos compared with those of mice.
The research was conducted by the Francis Crick Institute, who applied for permission to begin gene editing back in September 2015.
"It may take many years to achieve such an understanding, our study is just the first step", said Niakan.
They used genome "scissors" called CRISPR-Cas9 to snip out a gene called OCT4 from fertilised eggs.
Strict rules make it illegal to allow such a modified human embryo to develop beyond 14 days or be implanted. The majority were donated by couples who had completed their family, and wanted their surplus embryos to be used for research.
In the United Kingdom, strict ethical guidelines are in place for the use of eggs, sperm and embryos in research, regulated by the Human Fertilization and Embryo Authority.
In addition Oct4 seems to be closely linked to the generation of embryonic stem cells - "mother" cells in the early embryo with the potential to become any kind of tissue in the body. "Pluripotent" stem cells, which can be derived from human embryos, can form any type of tissue in the body and scientists use stem cell technology to create tissue that can fix damage or replace missing structures in the body. The researchers plan further work with CRISPR to find out exactly what genes OCT4 controls in the different cell types.
Director of the Crick Institute, Sir Paul Nurse, denied that this was the case. This could then improve IVF treatments for infertile couples and also help doctors understand why so many pregnancies fail.
Dr Kay Elder, the study co-author from the Bourn Hall Clinic, has said: "Successful IVF treatment is crucially dependent on culture systems that provide an optimal environment for healthy embryo development. There are critical differences in the levels and resulting developmental capacity of these embryos when essential genes are mutated", said Helen Claire O'Neill, programme director of reproductive science and women's health at University College London, who was not involved in the study.
"This is basic research which is providing us with a foundation of knowledge about early human development".
It is controversial because, say critics, it evokes a future in which humans can order "designer" babies with specific features, perhaps even intelligence. Funding was mainly provided by the UK Medical Research Council, Wellcome and Cancer Research UK.