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Human stem cells are used to create embryo-like structures

Understanding the earliest phases of human development necessitates research on human embryos. Currently, this research is based on excess embryos that have been willingly contributed by people who have had in vitro fertilization. Nonetheless, the availability of embryos and tight worldwide ethical time constraints on how long an embryo can develop in the laboratory limit this research (14 days maximum).

Caltech researchers have now used human stem cells to produce embryo-like structures. These structures are generated by mixing so-called pluripotent stem cells, which have the ability to develop into specialized types of cells, rather than normal embryos, which are formed by a combination of sperm and egg. Despite the fact that these embryo-like structures differ from real embryos in several ways, the technology used to produce them will be essential in answering outstanding issues about human development without the use of donated embryos.

The study was carried out in the lab of Magdalena Zernicka-Goetz, Caltech's Bren Professor of Biology and Biological Engineering, and published in the journal Nature Communications on September 21.

The structures are formed from a pluripotent stem cell that divides into several types of cells, which then self-assemble into a structure with a morphology that resembles that of an embryo, complete with embryonic and extra-embryonic components. Other researchers extracted pluripotent stem cells from a live human embryo, and the cells have since been kept in a laboratory environment.

Surprisingly, when given the correct conditions, the cells can still "remember" how to assemble into an embryo.

"The ability to create the basic framework of the embryo appears to be a built-in property of these first embryonic cells that they just cannot forget," Zernicka-Goetz explains. "However, either their memory isn't 100% accurate, or we don't yet have the ideal way for assisting the cells in recovering their memories. We still have a long way to go before we can get human stem cells to develop with the same level of precision as their mouse stem cell counterparts."

The ability to build embryo-like structures from stem cells eliminates the need for more donated embryos, and the structures can also be produced in vast quantities. As a result, this model system has the potential to lead to breakthroughs in our understanding of early embryonic development that are not limited by the scarcity of human embryos. It will be feasible, for example, to disrupt specific genes and examine the effects on the developmental process. This system can also be used to learn how distinct cellular components coordinate their development at the earliest stages, as well as the impact of this cellular cross-talk on later stages of development.

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