- Video report by ITV News Science Correspondent Alok Jha
Pioneering British scientists have discovered the key role played by a fertility "master gene" that could shed new light on the causes of infertility and miscarriage and improve the chances of people who want to have a baby using IVF.
Scientists at London's Francis Crick Institute discovered the vital role the Oct4 gene played in a viable pregnancy through editing DNA in human embryo - otherwise known as gene-editing.
This is the first time that genome editing has been used to study gene function in human embryos, which could help scientists to better understand the biology of early development in humans.
The research is controversial as it involves altering "germ line" genes in embryos that could be inherited by future generations.
The study, published in the journal Nature, found Oct4 appeared to be necessary for an embryo to become a blastocyst, a tiny ball of 200 cells that develops a week after conception and marks a key point in embryonic growth.
The research found fewer than a fifth of the test embryos reached the blastocyst stage without Oct4.
Only when an embryo successfully reaches the blastocyst stage does it stand any chance of implanting in the womb.
Strict rules govern fertility science.The Francis Crick Institute team was only given the go-ahead to conduct the research by the Human Fertilisation and Embryology Authority fertility regulator last year.
The research focused on the first seven days of development after fertilisation and none of the embryos were grown past seven days.
The scientists, who studied 41 human embryos donated by IVF patients, used the gene-editing tool Crispr/Cas9 to make precise cuts in DNA and deactivate Oct4.
The research also revealed 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.
So-called "pluripotent" stem cells whose fate can be manipulated in the laboratory could one day help the tens of thousand of genetic illnesses that have so far been beyond the reach of medical science.
Dr Kathy Niakan, who led the work published in the journal Nature, said: "Our research is the first time that genome editing has been used to understand the role of a gene in early embryonic development.
"This knowledge can be used to improve IVF treatment and improve our understanding of how some pregnancies fail."
Seen under a microscope, "knock out" embryos lacking Oct4 appeared to expand and contract repeatedly without progressing to the next stage of their development.
Dr Niakan said: "One way to find out what a gene does in the developing embryo is to see what happens when it isn't working.
"Now we have demonstrated an efficient way of doing this, we hope that other scientists will use it to find out the roles of other genes.
"If we knew the key genes that embryos need to develop successfully, we could improve IVF treatments and understand some causes of pregnancy failure.
"It may take many years to achieve such an understanding, our study is just the first step."
A handful of "special" cells in very immature embryos showed high Oct4 activity, the scientists found.
It was this sub-set of 10 to 20 cells that went on to produce the foetus and newborn baby after implantation.
Co-author Dr Norah Fogarty, also from the Francis Crick Institute, said: "We were surprised to see just how crucial this gene is for human embryo development, but we need to continue our work to confirm its role."
The scientists spent more than a year perfecting their technique with mice and human stem cells before starting work on human embryos.
They discovered important differences at the molecular level between developing embryos from the two species.
- You can find out more about Sohana, who featured in Alok Jha's report, by clicking here