From Stem Cells To Eggs (And Beyond)

Reporting in Science, researchers write that mouse stem cells can be transformed not only into egg cells—but into newborn pups. Sean Morrison, a stem cell expert at the University of Texas Southwestern, explains the stem cell's journey, and what it could mean for fertility and assisted reproduction.

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IRA FLATOW, HOST:

Up next, turning stem cell into mouse eggs. Scientists have been growing stem cells in the lab for nearly 15 years now. And in that time they've learned to transform stem cells into pretty much anything they wanted to - heart cells, liver cells, brain cells. But now a group of Japanese scientists has raised the bar by transforming mouse stem cells into mouse eggs. And not only do they look like eggs but they can be fertilized and developed into healthy mice.

Their research appears in the journal Science this week. How do they do it? Could the same thing work in humans? Just take a tiny piece of a woman's skin, turn it into fresh egg cells. Would it be ethical to do so? Joining me now to talk about these issues is Sean Morrison, director of the Children's Research Institute at University of Texas Southwestern Medical Center in Dallas. Welcome back to SCIENCE FRIDAY, Dr. Morrison.

SEAN MORRISON: Hey, Ira. Nice to talk to you again.

FLATOW: So give us a little thumbnail sketch of what happened. Scientists made egg cells from stem cells. How did they do that?

MORRISON: Well, they used either mouse embryonic stem cells or, as you know, it's also possible now to reprogram adult cells to have properties similar to embryonic cells - embryonic stem cells. Those are called induced pluripotent stem cells or IPS cells. They could use either of those kinds of pluripotent stems cells - pluripotent meaning they can make any cell type in the body. And they were able to generate mouse eggs or oocytes from the pluripotent stem cells. And, you know, what's particularly important about the paper, as you said, is that they confirmed that these were really functional eggs by using them in in vitro fertilization to make healthy adult mice.

FLATOW: And the mice themselves had offspring also?

MORRISON: Yes.

FLATOW: And those were healthy mice also?

MORRISON: As far as they know.

FLATOW: You know, this opens up all kinds of questions...

MORRISON: Yes.

FLATOW: ...about where do you move forward with something like this, because...

MORRISON: Well, there's two kinds of important implications. One is that this creates a system in which it's now really possible to study the differentiation of oocytes and the process by which they're formed. But secondly, if it's possible to do this with human pluripotent stem cells and if it's possible to identify an ethical path forward to really study the properties of those cells, it could really have important implications for how in vitro fertilization is done.

You could imagine for women who either can't make eggs or who can't make genetically healthy eggs that it could become possible to, as you said, take a small sample of normal cells, like from their skin, to derive induced pluripotent stem cells from those skin cells and then to use those cells to derive eggs that could be used during in vitro fertilization. Now, it's important to note that nobody has done this yet with human cells, and it's not clear whether it will be possible. But this paper that was published yesterday raises that possibility. And if it were possible, there are patients that - who could undergo more effective fertility treatment as a consequence.

The other issue, of course, is that the key experiment in the science paper was showing that the egg cells were functional by showing that they could be fertilized and they could be used to generate healthy mice. There would have to be a lot of thought given to how that could be tested with human cells because of course you don't want to fertilize human eggs as part of a research project in a laboratory.

You would only want to do that in the context of fertility treatment, and you would only want to do that if you had a pretty good reason to believe that the eggs had a chance of giving rise to healthy pregnancies.

FLATOW: That is a can of worms.

MORRISON: Yes.

FLATOW: Talking with Sean Morrison on SCIENCE FRIDAY from NPR. I'm Ira Flatow. Can you walk us through, how do you actually tell the stem cells, hey, turn into eggs now?

MORRISON: Well, they had a pretty complicated process that was described in their paper that involved, first, exposing the stem cells to certain signals in laboratory dishes, and then they mix the stem cells with cells from the mouse ovary so that the cells could be exposed to chemical signals that would normally be present in the ovary.

Then they took that mixture of cells and actually transplanted it back under - into the ovaries of mice, you know, inside their body, and then waited for the eggs to mature and then re-isolated the eggs and did in vitro fertilization with mouse sperm and then re-implanted the embryos into mice. And they were able to deliver successful pregnancies.

FLATOW: Could you apply the same the method to make sperm cells? If you're making egg cells, what about sperm cell?

MORRISON: Well, in fact, the same laboratory has already done this, shown that they could generate mouse sperm that was effective and functionally normal. And there are early indications that it's possible to take human pluripotent stem cells and generate cells that look a lot like sperm, although, you know, it hasn't been possible to do the key experiment to test whether or not the sperm-like cells that are derived from human pluripotent stem cells, whether they could, you know, really successfully fertilize an egg.

FLATOW: Would it be ethical to do this, you know, some of this work in humans? Would it take away some of the stigma about using embryonic stem cells?

MORRISON: Well, there's a whole lot of issues to consider in that I think a lot of people are going to have to involved in working through and thinking about under what circumstances it would be permissible to use this kind of approach in humans if the science really supports the idea that this kind of approach could generate cells that look like eggs from human pluripotent stem cells. I think the two key factors, I mean one key factor is that you would want to do this in the context of an effort, you know, for in vitro fertilization, in the course of reproduction rather than just generating embryos for the sake of research by fertilization.

And secondly, you would only want to go forward, I think, if you were sure enough from the preliminary studies that the eggs really looked healthy and normal and really felt like they had a chance of giving rise to successful pregnancies because you wouldn't want to engage in in vitro fertilization with a patient if there really wasn't much chance of having a successful pregnancy.

FLATOW: Is there any reason - going the opposite direction of thought, is there any reason to believe this would not work in humans?

MORRISON: You know, there have been so many twists and turns in the plot of pluripotent stem cell biology over the past 10 years that I wouldn't bet against anything, and I also don't think we should be in the business of making sure predictions about exactly what's going to happen. It's possible that what's described in this paper won't work on human cells. But it wouldn't be surprising if it did.

FLATOW: All right. We're going to leave it right there. And thank you very much for taking time to be with us today. Some interesting food for thought this Friday. Thanks a lot.

MORRISON: All right. Nice talking to you, Ira.

FLATOW: Sean Morrison, director of the Children's Research Institute at the University of Texas Southwestern Medical Center in Dallas. That's about all the time we have today. A quick reminder - a couple of quick reminders. Go to our website at sciencefriday.com. We have our video pick of the week up there, and there are some battling beetles that I'm sure you're going to want to watch as they battle all about - well, size means everything on these beetles. You're going to want to see that up on our website at sciencefriday.com.

Also, the SCIENCE FRIDAY Book Club, we're meeting again on October 26. Our next book is "Surely You're Joking, Mr. Feynman!" by Richard Feynman. We just mentioned him and talked about what a great writer he was and how thoughtful he was. You can get your copy and start reading it and then join our conversation a few weeks from now on our book club date. That's going to be October 26.

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