Between the 7th and 14th day, scientists identified important molecular events in the developing human embryo – one of the most mysterious and at the same time most critical phases of our development.
The second week of pregnancy is a critical stage in embryonic development or embryogenesis. Development failure during this period is a major cause of early pregnancy loss. Knowing more about it can help scientists understand how it can go wrong and take steps to correct problems.
The pre-implantation period before the developing embryo implanted in the mother’s uterus was extensively studied in the laboratory on human embryos. On the seventh day, the embryo has to implant itself in the uterus in order to survive and develop. Very little is known about the development of the human embryo after implantation as it becomes inaccessible to study.
As a pioneering work by Professor Magdalena Zernicka-Goetz and her team, a technique was developed in 2016 to cultivate human embryos outside the mother’s body beyond implantation. This was the first time that human embryos could be examined up to the 14th day of development.
In a new study, the team worked with colleagues at the Wellcome Sanger Institute to find out what is happening at the molecular level at this early stage in embryogenesis. Their results provide the first evidence that a group of cells outside the embryo, called the hypoblast, sends the embryo a message that initiates the development of the head-tail axis.
When the body axis begins to form, the symmetrical structure of the embryo begins to change. One end is designed to develop into the head end and the other the “tail”.
The new results published in the journal today Nature communication, show that the molecular signals involved in the formation of the body axis are similar to those in animals, despite significant differences in the positioning and organization of the cells.
“We have revealed the patterns of gene expression in the developing embryo immediately after implantation in the uterus, reflecting the numerous conversations that take place between different cell types during the development of the embryo at these early stages,” said Professor Magdalena Zernicka-Goetz Department of University of Cambridge Physiology, Development and Neuroscience and senior author of the report.
She added, “We looked for the gene conversation that allows the head to develop in the embryo and found that it was initiated by cells in the hypoblast – a disc of cells outside the embryo. They send the message to neighboring embryo cells, which respond by saying, ‘Okay, now let’s lie down to one side to develop towards the head end.’ “
The study identified the gene conversations in the developing embryo by sequencing the code in the thousands of messenger RNA molecules made by individual cells. They recorded the developing molecular profile of the developing embryo after implantation in the uterus and showed the progressive loss of pluripotency (the ability of embryonic cells to produce any type of cell in the future organism) while determining the fate of different cells.
“Our goal has always been to provide insights into the very early development of human embryos in a shell in order to understand how our life begins. By combining our new technology with advanced sequencing methods, we have delved deeper into the most important changes taking place in this incredible phase of human development where so many pregnancies unfortunately fail, ”said Zernicka-Goetz.
This research was carried out under the supervision of the UK Human Fertilization and Embryology Agency and with the approval of a local research ethics committee.