To study human development researchers need access to human embryos. These are provided by individuals undergoing in vitro fertilization, with any surplus embryos donated for use in research. Current regulations limit the development time in the laboratory to 14 days. There is naturally a limited supply of donated embryos, so having a more readily available supply, which can also be used for longer, would be of great value to researchers to study the earliest stages of human development.
Researchers at the California Institute of Technology (Caltech) may have the solution. They have developed embryo-like structures from human stem cells. These embryo-like structures are naturally different from donated embryos but share important characteristics. They are not created by the fusion of a sperm and an egg, instead they are created by combining pluripotent stem cells – cells that have the ability to develop into other cell types.
The technique developed by researchers in the lab of Magdalena Zernicka-Goetz, Bren Professor of Biology and Biological Engineering at Caltech, allows the pluripotent stem cells to develop into two cell types which self-assemble into a structure that resembles a human embryo that has both embryonic and extra-embryonic tissues.
The stem cells used were isolated from a human embryo initially and have been maintained in the lab. When provided with the right environmental conditions, the cells spontaneously form an embryo-like structure.
“The ability to assemble the basic structure of the embryo seems to be a built-in property of these earliest embryonic cells that they are simply unable to ‘forget,'” said Zernicka-Goetz. “Nevertheless, either their memory is not absolutely precise or we don’t yet have the best method of helping the cells recover their memories. We still have further work to do before we can get human stem cells to achieve the developmental accuracy that is possible with their equivalent mouse stem cell counterparts.”
There are key advantages to using these embryo-like structures over donated embryos. Perhaps most importantly, they can be generated in large numbers so research need not be constrained by the limited availability of donated human embryos. The large numbers mean it would be possible to make changes to gene expression to determine how individual genes affect early human development, which could lead to important breakthroughs in understanding of early embryonic development.
It would also be possible to use the system to determine how different cellular components coordinate their development at the earliest stages of embryogenesis and the impact of this cellular cross-talk at later developmental stages.
You can read more about the research in the paper – Reconstructing aspects of human embryogenesis with pluripotent stem cells – which was recently published in Nature Communications. DOI: 10.1038/s41467-021-25853-