Using reprogrammed naïve stem cells, a team of scientists grew an embryo model that looks similar to a natural 14-day-old human embryo without using sperm, eggs, or a uterus.
Despite the ethical and moral implications of embryonic research, understanding the nuances of growth could help scientists learn more about the development of genetic conditions and congenital disabilities or why some in vitro fertilization (IVF) attempts are unsuccessful.
Recently, a team of researchers from The Weizmann Institute of Science in Israel created replicas without sperm, eggs, or a womb. The scientists say this lab-grown embryo mimics all the critical structures of a 14-day-old human embryo.
An unedited version of their research was published on September 6 in Nature.
To create the embryo model, the team used naïve stem cells reprogrammed to become any tissue type. Then, they added specific chemicals to turn on genes that transformed the stem cells into cells that typically occur in early development. These included trophoblast cells (placenta), epiblast cells (fetus), hypoblast cells (yolk sac), and extraembryonic mesoderm cells (supportive tissue).
The researchers combined 120 of these cells using a specific ratio in a lab dish under precise conditions, allowing them to grow until they were similar to a 14-day-old human embryo. This is the stage when embryos begin to develop organs and other complex body structures.
The synthetic embryo had characteristics of a natural human embryo, including the yolk sac, placenta, chorionic sac, and other external tissues that play a role in embryonic growth. It also emitted hormones that turned a pregnancy test positive in the lab.
In a press release, lead researcher Professor Jacob Hanna from the Weizmann Institute of Science said, "The drama is in the first month, the remaining eight months of pregnancy are mainly lots of growth. But that first month is still largely a black box. Our stem cell–derived human embryo model offers an ethical and accessible way of peering into this box. It closely mimics the development of a real human embryo, particularly the emergence of its exquisitely fine architecture."
The researchers note that their synthetic embryo model cannot successfully implant in a womb, and pregnancy using these models would be impossible.
"An embryo is not static. It must have the right cells in the right organization, and it must be able to progress — it's about being and becoming," says Hanna. "Our complete embryo models will help researchers address the most basic questions about what determines its proper growth."
In addition, in 2022, University of Cambridge researchers created a mouse embryo model using stem cells that developed a beating heart and beginnings of brain growth.
- Nature. Complete human day 14 post-implantation embryo models from naïve ES cells.
- Weizmann Institute of Science. Human Embryo Models Grown from Stem Cells.
- University of Cambridge. ‘Synthetic’ embryo with brain and beating heart grown from stem cells by Cambridge scientists.