Understanding aspects of early human development is crucial. This approach is not only useful for improving reproductive technologies, but 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 trofectoderma. The trofectoderm in question surrounds a cavity containing a cluster of cells called the inner cell mass (ICM). This is also what causes most of the placenta.
A promising approach
It must be acknowledged that our knowledge of the early development of mammals has for many years been limited to the observation and manipulation of human embryos and animals – including mice. However, the relatively short time frame for analysis makes it difficult.
There are both 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 progress 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, placenta and supporting tissue, the yolk sac. To do this, the researchers used cells that represent lines in the human blastocyst. They also improved culture protocols.
Division of human cells under a microscope. Photo: Shutterstock / Anusorn Nakdee
In particular, skin cells are placed in 3D culture vessels called Aggrewell plates. In both studies, about 20% of the cell aggregates formed blastoids after 6 to 8 days. Although this is a major breakthrough in our efforts to understand the early stages of human development, this type of research remains challenging because there is currently no optimal culture system that would mimic human perimplantation implantation.
On the other hand, strict ethical rules prevent the cultivation of human embryos for more than 14 days, the moment the structures associated with gastrulation begin to appear. In any case, we hope that this research on human blastoids will one day pave the way for the development of embryos. The input is important because it can not only help solve some basic biological issues, but also help model the disorders that occur in early pregnancy.