By John Kerr 19/10/2016

The successful production of functional mouse eggs entirely in cell culture by Japanese scientists has been lauded as a technical feat, but there might be some tricky issues to tackle before even thinking about progressing the technology to humans.

In a paper published in Nature yesterday Katsuhiko Hayashi from Kyushu University and colleagues reported the results of their experiments using mouse cells.

The researchers were able to take mouse skin cells and reprogram them to become embryonic-like stem cells, replicating earlier studies. However, the next step was a world first: by placing the stem cells in just the right environment, the researchers were able to trigger development into mature eggs in the lab.

Hayashi and co were then able to show these eggs were viable; a small number of the eggs they created, once fertilised and implanted in a female mouse, resulted in normal healthy offspring.

Healthy offspring. Hayashi et al. (2016)
Healthy offspring. Hayashi et al. (2016)

The outcome marks an important step in reproductive biology, this is the first time functional eggs have been grown outside of a mouse.

Read more about the research on

So what next? The authors give a suitably measured suggestions of future research in their conclusions:

“…the culture system used here will provide an important platform for analysing the gene functions underlying oogenesis in addition to providing clues to the development of a similar culture system in other species.”

Will it work in humans?

Now that in vitro-created eggs has been accomplished in mice, this inevitable question arises. The researchers have repeatedly warned that any human applications are a long way off. However, the fact remains that much research in reproductive biology is undertaken with medical endpoints in mind. As Science magazine reports:

If scientists could use a similar technique to transform human [stem] cells into fertile egg cells, it could offer new options for infertile woman, such as those who have gone through egg-destroying chemotherapy.

“The study used mouse cells but if it can be translated to humans, and shown to be safe, it could theoretically provide a treatment for female infertility in the future,” says Dr Teresa Holm, from the University of Auckland, speaking to the Science Media Centre.

“In the meantime, this approach provides a valuable new tool to study the normal biology of egg formation and how this process goes awry in certain diseases or birth defects.”

Speaking to Nature News Dr Jacob Hanna, a stem cell biologist at the Weizmann Institute of Science in Israel, described the research as “truly amazing” and suggested that repeating the process in humans might not be far off. “I do not think it is going to prove much more complex,” he said.

Nature News reported further:

If the Hayashi protocol works with human cells, it could in principle be used to make eggs from a man’s skin cells, Hanna says — adding that, as a pro-LGBT rights activist, he thinks that this option is “legitimate to explore when the right time comes.” Hayashi, however, has yet to use male skin cells to produce eggs in mice.

Hayashi thinks that “oocyte-like” human eggs might be produced within ten years, but he doubts that they will be of sufficient quality for fertility treatments. “It is too preliminary to use artificial oocytes in the clinic,” he says, cautioning that his study showed that the artificial mouse eggs were often of low quality. He worries that such eggs might create genetically abnormal embryos, and potentially abnormal offspring. In the study, only 3.5% of the early embryos created from artificial eggs gave rise to pups — compared with 60% of eggs that were matured inside a mouse.

But debate over the ethics of such a technology should begin now, says Azim Surani, a pioneer in the field at the University of Cambridge, UK. “This is the right time to involve the wider public in these discussions, long before and in case the procedure becomes feasible in humans,” he says.


Featured image credit: Hayashi et al. (2016)