Fertile eggs created from stem cells


These mice came from eggs created in the lab by scientists using embryonic stem cells. Photo by Kasuhiko Hayashi.

You may read about this paper already, about scientists turning stem cells into fertile eggs (for example, this article at NPR). And of course, it deserves the hype. This is certainly a big breakthrough in stem cell research–especially induced pluripotent stem (iPS) cell research. iPS cells are similar to embryonic stem cells, except that they can be made out of any cell in the body.

This means two big things: first, there’s no need to destroy an embryo to get these stem cells. Second, after turning the stem cells into any tissue in the body (including sperm and eggs, apparently), they can be implanted back into the original donor. Why is this second point so important? Let’s say you need a new kidney because yours are failing. In theory, you could have stem cells made from your skin and then have those grown into a brand new kidney that could be put back inside you. It would be like being your own organ donor! While this hasn’t been done yet, scientists have shown that a tiny unborn baby sized kidney can be grown this way.

So, back to the eggs and sperm: does this mean we can now dispense with sex altogether and make sperm and eggs at will? Or that gay and lesbian couples could make both sets of gametes (between the two of them) for baby-making? Not quite yet.

The sperm and eggs made from mouse stem cells still required live animals of the correct sex to finish their development. The stem cells were used to make sperm up to a very early developmental stage, and then implanted into testes to finish becoming usable sperm. The eggs needed even more help. After getting them to the early developmental stage, the not-quite-eggs had to be mixed with helper cells from ovaries of female mouse embryos. This created a “reconstituted ovary” that could then be transplanted into a female mouse. In other words: we’re a long way away from using this technology to create personalized eggs and sperm in a dish (though it will probably happen eventually).

The major importance of this research (together with the earlier creation of sperm cells from embryonic stem cells) is that we can use them to understand what actually goes on inside a germ cell when it becomes either a sperm or egg. And understanding that will take us a lot further into understanding what happens when something goes wrong in the process.

References:
Katsuhiko Hayashi, Sugako Ogushi, Kazuki Kurimoto, So Shimamoto, Hiroshi Ohta, & Mitinori Saitou (2012). Offspring from Oocytes Derived from in Vitro Primordial Germ Cell–Like Cells in Mice Science DOI: 10.1126/science.1226889

Hayashi K, Ohta H, Kurimoto K, Aramaki S, & Saitou M (2011). Reconstitution of the mouse germ cell specification pathway in culture by pluripotent stem cells. Cell, 146 (4), 519-32 PMID: 21820164

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