Although scientists know a lot about the process of human embryo implantation, it had never been recorded in real time, until now. Now that investigators can observe it in action, they may be able to gain new insights into why it can fail. Implantation failure is a major cause of infertility, thought to cause about 60% of miscarriages. The work has been reported in Science Advances.
'We have observed that human embryos burrow into the uterus, exerting considerable force during the process. These forces are necessary because the embryos must be able to invade the uterine tissue, becoming completely integrated with it,” explained senior study author Samuel Ojosnegros of the Institute for Bioengineering of Catalonia (IBEC). “It is a surprisingly invasive process. Although it is known that many women experience abdominal pain and slight bleeding during implantation, the process itself had never been observed before.”
During implantation, the embryo secretes enzymes to break down tissue and clear its path, but force is also necessary to get into the deeper layers of the uterus. There is lots of collagen in this tissue, a tough protein that is a major part of cartilage.
The embryo has to work its way through, and form special tissues that are linked to the blood vessels of the mother, added Ojosnegros.
The forces exerted by human embryos that are implanting remodels the local tissue, which is reorganized.
“We hypothesize that contractions occurring in vivo may influence embryo implantation,” noted first study author Amélie Godeau, a researcher in the Ojosnegros lab.
This research was conducted with human and mouse embryos, in a research model that enables the viewing of implantation in a controlled environment. The model consists of an artificial matrix that mimics the natural, biological environment, in part by using lots of collagen, and other proteins that are normally present. The embryo was tagged with fluorescent markers to reveal structural and biological details. In the image at the top of this article, the protein OCT4 is marked in green, GATA6 appears as magenta, and the nuclear DNA is seen in blue, which is marking DAPI.
In mice, the embryo contacts the uterus, which forms a crypt around it, linking the embryo and uterus. But in humans, the embryo pushes into the uterine tissue, penetrating it so it can then slowly grow from there, outward.
Sources: IBEC, Science Advances