Understanding aspects of early human development is critical. Not only is this approach useful for improving reproductive technologies, but it could ultimately help prevent miscarriages and birth defects.
During the first few days of development, human embryos form a structure called a blastocyst. This has an outer layer of cells called the trophectoderm. The trophectoderm in question surrounds a cavity that contains a cluster of cells called the internal cell mass (ICM). It is also what causes most of the placenta to form.
A promising approach
It must be recognized that our knowledge of early mammalian development has for many years been limited to the observation and manipulation of human embryos and animals – including mice. However, the relatively short timeframe for analysis makes it difficult.
There are also ethical and legal restrictions. The use of techniques using in vitro cultured cells to create embryo models is therefore an interesting approach. Two studies published in the journal Nature show significant advances in this area.
Structures comparable to natural blastocysts
The two teams behind this science actually focused on exploring the synergy between stem cells and developmental biology to create human blastoids. These are structures that are more or less similar to natural blastocysts and at the beginning of development produce the embryo, the placenta and a supporting tissue, the yolk sac. To do this, the researchers used cells representative of lines in the human blastocyst. They also improved the culture protocols.
Division of human cells under the microscope. Photo credit: Shutterstock / Anusorn Nakdee
A big challenge
In particular, the skin cells were placed in 3D culture dishes called Aggrewell plates. In both studies, about 20% of the cell aggregates formed blastoids after 6 to 8 days. While this is a major breakthrough in our efforts to understand the early stages of human development, this type of research remains challenging as there is currently no optimal culture system to mimic peri-implant human implantation.
On the other hand, strict ethical rules prevent the cultivation of human embryos beyond 14 days, the moment the structures associated with gastrulation begin to appear. In any case, let’s hope that this research on human blastoids will one day pave the way for embryo development. The input is considerable as it can not only help solve some basic biological questions, but also help model the disorders that occur at the beginning of pregnancy.