Scientists Create Human Embryo Models Using Stem Cells

Researchers hope that models derived from stem cells will deepen the understanding of what happens during a critical stage of embryo development when many pregnancies are lost.

The models, described in two separate studies published in the peer-reviewed journal Nature on June 27, do not have the potential to develop into human beings, as they are derived from stem, not reproductive cells.

Nevertheless, the groundbreaking discoveries may reveal some of the causes of genetic disorders and help to reduce the need for donated human embryos that have been used in the research thus far.

The researchers at the University of Cambridge created the embryo model from pluripotent stem cells that replicate some developmental processes that occur during the second week of pregnancy. This is an important time when the embryo implants into the uterus, but it can be very hard to see. Many pregnancies are lost during this stage.

A better understanding of early developmental processes holds the potential to reveal some of the causes of human birth defects and diseases and to develop tests for these in pregnant women. Moreover, embryo models can help researchers gain basic knowledge of the developmental origins of organs and specialized cells such as sperm and eggs.

"This exciting development allows us to manipulate genes to understand their developmental roles in a model system. This will let us test the function of specific factors, which is difficult to do in the natural embryo," says Professor Magdalena Zernicka-Goetz in the University of Cambridge's Department of Physiology, Development, and Neuroscience, who led the work.

Yale School of Medicine scientists who created another stem cells-derived embryo model say it has over 70% efficiency, meaning that the stem cells aggregate correctly over roughly 70% of the time.

The model will allow scientists to examine how embryonic and extraembryonic components interact in the early stages of embryo development, providing a unique look at the molecular and cellular processes that occur.

"If you want to understand human development, you need to look at the human system. This work is really important because it's giving us direct information about our own species," says Berna Sozen, Ph.D., an assistant professor of genetics at Yale School of Medicine.

After the studies made headlines around the world, the International Society for Stem Cell Research (ISSCR) released a statement advising against using the term "synthetic embryo" to describe embryo models, explaining that they "cannot and will not develop to the equivalent of postnatal stage humans." It also reiterated that the ISSCR Guidelines prohibit the transfer of any embryo model to the uterus of a human or an animal.

Henry Greely, director at the Center for Law and the Biosciences at Stanford University, says that legally, what an embryo is depends on the law involved, and each law will need to be examined.

"I suspect these (embryo models) would be considered embryos under, say, the US Dickey-Wicker funding limit," Greely tweeted.

Dickey-Wicker Amendment, first adopted in 1996, prohibits federal funds from being used to support research in which human embryos are destroyed or knowingly subjected to risk of injury or death. According to the amendment, the term "human embryo" includes any organism that is derived by fertilization, parthenogenesis, cloning, or any other means from one or more human gametes or human diploid cells.

However, the researchers who created the embryo models say they have no plans to use them for reproductive purposes, as it would be extremely dangerous.


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