Researchers have used human stem cells in the laboratory to mimic the earliest stage of human embryo growth yet. Multiple research groups have reported successful growth of balls of cells that resemble human blastocysts. Blastocysts form about four days after a human egg is fertilized by sperm. Two research groups published the results of their studies this week, while two other groups have reported similar results that have yet to be peer-reviewed.
Researchers say experiments such as these shine light into a crucial window in the development of humans and give the opportunity for researchers to understand pregnancy loss and infertility without the need to experiment on human embryos. Researcher Jianping Fu from the University of Michigan in Ann Arbor says that this is an important milestone. Some of the understanding that science has about this early stage of development has been learned from directly studying human embryos.
However, access to embryos is limited and tightly regulated due to ethical considerations. However, blastocysts grown in the laboratory from human stem cells differ from human embryos and may avoid ethical limits on traditional human embryo research. Scientists believe that increasing access to this type of research could lead to new breakthroughs. Researchers say they don’t believe the new blastocyst-like structures can develop into a complete embryo.
In the past, scientists were able to grow blastocysts in the lab from mouse stem cells, but mice have different developmental pathways than humans. That means resulting structures aren’t a perfect model of human development. Blastocysts would implant in the wall of the uterus at around seven or eight days. At that point, it has an outer layer of cells that give rise to the placenta, and a clump of cells within have the potential to develop into a fetus.
Researchers have been successful in the past using human embryonic stem cells to look at later stages of embryo development around 18 to 20 days after the blastocyst has implanted. The experiment is looking into the earliest stage of development ever modeled in a lab.