http://news.independent.co.uk/uk/health ... ory=370020
Embryo 'glue' study may raise chances of successful births
By Steve Connor Science Editor
17 January 2003
Scientists have discovered the "glue" that helps to stick an early human embryo to the wall of the womb – a critical first stage in every successful pregnancy.
The findings might eventually be used to improve the success rates of in vitro fertilisation (IVF) as well as lowering the risk of pre-eclampsia, the most common cause of death in first-time pregnancies.
A week-old embryo must attach itself firmly to the womb to trigger the correct growth of the placenta. These first stages of implantation are critical, yet little is known on how the embryo does it.
Researchers from the University of California at San Francisco have identified the molecular sticking process that starts to take place when an early embryo is ready to implant itself in the womb about six days or more after fertilisation.
Failure to implant properly is estimated to result in the failure of about three in every four pregnancies, so understanding the first critical step could provide important insights into ways of improving the chances of a successful birth.
The scientists found that molecules on the surface cells of the embryo and in substances secreted in the lining of the womb began to interact to create a viscous environment, according to Susan Fisher, who led the study published in the journal Science.
"It's like a tennis ball rolling across a surface covered in syrup. The embryo's journey along the uterine wall is arrested by the sticky interaction," Professor Fisher said.
The scientists found that the outer cells of the embryo began to produce a protein called L-selectin, while the cells of the uterus became enriched with carbohydrates, which had a tendency to stick to the protein.
By coating latex beads with the type of carbohydrates found in the uterus lining, the scientists demonstrated they stuck readily to the outer cells of an embryo, called the trophoblast, at the critical stage of development when it was normally ready for implantation.
A continual process of sticking and unsticking slows down the embryo on its journey through the uterus until it eventually stops and an implantation begins. Implantation proper is caused by cells from the embryo invading and replacing the cells of the uterus lining in order to form a placenta.
A similar sticking process was first identified about 10 years ago. It allows white blood cells to attach themselves to the walls of a blood vessel when they reach an area of inflammation. The belief now is that embryo implantation is essentially the same molecular interaction.
Professor Fisher said that knowing how implantation was triggered should help to improve the pregnancy rates among IVF mothers, whose embryos frequently failed to implant. It should also help to avoid pre-eclampsia, which she said could be caused by the placenta not attaching properly to the womb, leading to oxygen starvation of the foetus and raised the blood pressure of the mother.
The work could help to explain why some women have a low fertility. They may have a uterus lining that does not produce the necessary carbohydrate molecules to allow the early embryo to stick to the womb. The scientists demonstrated that cells taken from the uterine lining were sometimes more receptive to implantation than at other times.
