Eggciting News: Scientists developed fertilized eggs from mouse stem cells

A really eggciting science story came out early this week that’s received a lot of attention. Scientists in Japan reported in the journal Nature that they’ve generated egg cells from mouse stem cells, and these eggs could be fertilized and developed into living, breathing mice.

This is the first time that scientists have reported the successful development of egg cells in the lab outside of an animal. Many implications emerge from this research like gaining a better understanding of human development, generating egg cells from other types of mammals and even helping infertile women become pregnant.

Making eggs from pluripotent stem cells

The egg cells, also known as oocytes, were generated from mouse embryonic stem cells and induced pluripotent stem cells derived from mouse skin cells in a culture dish. Both stem cell types are pluripotent, meaning that they can generate almost any cell type in the human body.

After generating the egg cells, the scientists fertilized the eggs through in vitro fertilization (IVF) using sperm from a healthy male mouse. They allowed the fertilized eggs to grow into two cell embryos which they then transplanted into female mice. 11 out of 316 embryos (or 3.5%) produced offspring, which were then able to reproduce after they matured into adults.

mice

These mice were born from artificial eggs that were made from stem cells in a dish. (K. Hayashi, Kyushu University)

Not perfect science

While impressive, this study did identify major issues with its egg-making technique. First, less than 5% of the embryos made from the stem-cell derived eggs developed into viable mice. Second, the scientists discovered that some of their lab-grown eggs (~18%) had abnormal numbers of chromosomes – an event that can prevent an embryo from developing or can cause genetic disorders in offspring.

Lastly, to generate mature egg cells, the scientists had to add cells taken from mouse embryos in pregnant mice to the culture dish. These outside cells acted as a support environment that helped the egg cells mature and were essential for their development. The scientists are working around this issue by developing artificial reagents that could hopefully replace the need for these cells.

Egg cells made from embryonic stem cells in a dish. (K. Hayashi, Kyushu University)

Egg cells made from embryonic stem cells in a dish. (K. Hayashi, Kyushu University)

Will human eggs be next?

A big discovery such as this one immediately raises ethical questions and concerns about whether scientists will attempt to generate artificial human egg cells in a dish. Such technology would be extremely valuable to women who do not have eggs or have problems getting pregnant. However, in the wrong hands, a lot could go wrong with this technology including the creation of genetically abnormal embryos.

In a Nature news release, Azim Surani who is well known in this area of research, said that these ethical issues should be discussed now and include the general public. “This is the right time to involve the wider public in these discussions, long before and in case the procedure becomes feasible in humans.”

In an interview with Phys.org , James Adjaye, another expert from Heinrich Heine University in Germany, raised the point that even if we did generate artificial human eggs, “the final and ultimate test for fully functional human ‘eggs in a dish’ would be the fertilization using IVF, which is also ethically not allowed.”

Looking forward, senior author on the Nature study, Katsuhiko Hayashi, predicted that in a decade, lab-grown “oocyte-like” human eggs will be available but probably not at a scale for fertility treatments. Because of the technical issues his study revealed, he commented, “It is too preliminary to use artificial oocytes in the clinic.”

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