Mice grown from stem cells
In what embryologists everywhere are hailing as a scientific "tour de force", Japanese researchers announced this week that they have successfully turned skin cells into eggs cells that are capable of being fertilised and giving rise to healthy young mice. Previously this had been achieved only by implanting cells into the ovaries of living animals. This new breakthrough, on the other hand, was achieved completely external to the body using a culture system. Dusko Ilic is a stem cell biologist at Kings College London. He wasn't involved in this piece of research but he took Chris Smith through what Katsuhiko Hayashi, the author of the new study, had done...
Dusko - This is a Japanese group that's worked a long time on this problem and the problem is how you can make eggs in a laboratory using stem cells.
Chris - Now why is that an intractable or long standing problem - why can't we do that?
Dusko - We don't know enough about it. To make eggs or sperm is probably one of the most complicated puzzles.
Chris - And what have this group actually done that means that we are a further step down the road?
Dusko - Several years ago they published their first report in which they used cells from a mouse tail. They fiddled with them in some way to revert them to embryonic state.
And then they took those cells and put in mouse ovaries or mouse testes and those they put in the mouse ovaries after a month they become eggs. In this report they didn't use live animals; they just took the ovary, put it in a dish, put it together with the stem cells and they got eggs.
Chris - So just by taking a stem cell, by putting that in the right sort of melia - the right environment - an ovary or ovarian tissue, this is what then triggers those stem cells to then turn into egg-like cells again?
Dusko - Exactly, that is correct. So before they have to put in the ovary but now they figure out how to keep the tissue in dish and so in the right environment the cells know what to do.
Chris - What is the nature of the signal then or why do you think that putting these stem cells into the environment of cells that you would find in an ovary - why is that sufficient to make these stem cells then turn into some kind of egg-like cell?
Dusko - Because the ovary is not only made from eggs. There are different cell types and so they secrete different factors. They give signals and tell their neighbours what to do this is like a small tightknit environment. So like a village and they know what to do and influence each other.
Chris - And this influence is in the correct direction to make these stem cells turn into eggs. But are the eggs that are produced this way viable - in other words are they not just looking like eggs, can they behave like eggs and be fertilised by a sperm cell?
Dusko - In this report, they show that it is possible. They got from a certain percentage of eggs, they got live pups.
Chris - Right, and were those pups themselves potentially fertile or have they not done that experiment yet to show that it's not just one generation you can make, you are actually making fertile offspring?
Dusko - They didn't do this experiment yet. But the pups looked fine, they look healthy, and they showed that they can make from those eggs stem cell lines. Everything seems to be okay and in place.
Chris - And why is this important - why should we hail this as a breakthrough, if indeed we should?
Dusko - I think this should. There is two different, very important issues around this. So first this will help us to study and understand and find how to treat infertility cases in humans. Secondly, it may help to revive endangered animal species.
Chris - Because we could potentially take an adult cell from the animal we want to conserve and, even if it's male, you could, presumably, with the right culturing you could turn that into eggs cells from a male?
Dusko - Absolutely. So it has to be male because males have X and Y chromosomes (female and male chromosomes), so they can produce eggs and sperm. From a female you can get only eggs so that would be problem.
Chris - Well given this success story then what are the outstanding questions that you, as a specialist in this area, would like to see answered before you're comfortable that a) this is working the way they say it's working, and b) that we could consider extrapolating this onto say a human?
Dusko - I don't think that we should rush towards extrapolating to humans, so there is a lot of things to answer yet. First, if you're working with humans, how you can get human ovarian tissue. So we first have to go to the next step, which means culturing and understanding how to direct stem cells to make eggs or sperm without any other tissue present in the culture, and that would take probably years. Only after that can we see how it works - not only in mice maybe in other animals. So it will take years before we can even consider humans.