My novel, In Vitro Lottery, has infertility and IVF as its central theme, so I'm always fascinated to learn about new research in that area. The latest comes from a group in Japan, who have successfully managed to re-program mouse skin cells into mature eggs, with all stages taking place 'in the dish'.
Primordial germ cells (PGCs), the pre-cursors for eggs, were first made from embryonic stem cells (ESCs) or induced pluripotent stem cells (iPSCs) and published in 2013, but had to be transferred to an adult mouse's ovary to complete maturation to eggs that could be fertilised successfully .
Cells do not develop and differentiate in isolation, and require signals from the cells and environment surrounding them to know what genes they need to switch on and off. Earlier this year, a separate paper  overcame this hurdle by re-creating this environment using ovarian tissue extracted from developing mice.
Now, a new paper from Katsuhiko Hayashi's research group  (summarised in ) has put all of this together to make an unbroken chain of stem cells to mature eggs, and through IVF, live offspring.
It's still very much a proof of principle at this stage, as only 3.5% of eggs in the study produced offspring, compared to 61% when adult host mice were used to incubate the PGCs, even though fertilisation rates were similar. The failures occurred at various stages of development, ranging from the first few cell divisions to late on in development, possibly due to incorrect cell division or genes not being controlled correctly.
Re-creating the mouse female reproductive system in a dish, from . (c) Macmillan Publishers Limited
Although this technique holds long-term promise for certain types of infertility in humans, it is mainly concerned with unlocking the basic science on how eggs develop and mature in nature. The fact that the method now exists, though, raises potentially very serious ethical issues.
Currently, for the process to work it requires the support cells to come from the ovaries of developing mouse embryos. This is, obviously, not an option in humans, unless you are writing a science-fiction story where one child is sacrificed for the benefit of another. I don't think many people would be comfortable living in that kind of a world!
One way to overcome this is to use stem cells from adults and re-program them to do the same job, as the paper suggests, but this is not currently possible.
The currently low success rate and possibility of developmental issues or abnormalities is also something that would need to be addressed.
Still, science is a step-by-step process and over the coming years the technique will be improved and optimised, possibly eventually becoming a standard technique in mouse transgenic research laboratories around the world. If they can solve the support-cell issue, this could have major benefits for the 3Rs in developmental genetics research.
Whether the debate on any human-based applications will have reached any kind of consensus by then, remains to be seen.
-- Ed Ryder
 Hayashi, K., & Saitou, M. (2013). Generation of eggs from mouse embryonic stem cells and induced pluripotent stem cells. Nature Protocols, 8(8), 1513–24. https://doi.org/10.1038/nprot.2013.090
 Morohaku, Kanako, Ren Tanimoto, Keisuke Sasaki, Ryouka Kawahara-Miki, Tomohiro Kono, Katsuhiko Hayashi, Yuji Hirao, and Yayoi Obata. 2016. “Complete in Vitro Generation of Fertile Oocytes from Mouse Primordial Germ Cells.” Proceedings of the National Academy of Sciences of the United States of America 113 (32). National Academy of Sciences: 9021–26. doi:10.1073/pnas.1603817113.
 Hikabe, O., Hamazaki, N., Nagamatsu, G., Obata, Y., Hirao, Y., Hamada, N., … Hayashi, K. (2016). Reconstitution in vitro of the entire cycle of the mouse female germ line. Nature. https://doi.org/10.1038/nature20104
 Cyranoski, D. (2016). Mouse eggs made from skin cells in a dish. Nature, 538(7625), 301–301. https://doi.org/10.1038/nature.2016.20817