Studying Regeneration for New Limbs, Organs

ANDREA SEABROOK, host:

From NPR News, this is ALL THINGS CONSIDERED. I'm Andrea Seabrook.

Legend has it that salamanders are born in fire and that they have magical abilities to renew and nourish themselves in flames. Real salamanders are none too fond of fire but they do have amazing abilities to renew and regenerate themselves. So this week on Science Out of the Box, why can salamanders regrow limbs and why can't we?

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SEABROOK: David Gardiner is a research biologist at the University of California Irvine. His specialty is regeneration, and he joins us from member station KUCI in Irvine. Thanks for joining us, David Gardiner.

Mr. DAVID GARDINER (Research Biologist, University of California Irvine): My pleasure to be here.

SEABROOK: So I guess the first and most obvious question is do we know how salamanders regrow their limbs?

Mr. GARDINER: Well, if we knew how to do that we'd be knowing how to regrow our own limbs. So the simple answer is no. But we know a lot about them. We're learning more all the time.

SEABROOK: So, what do we know? I mean, what do you do in the lab?

Mr. GARDINER: Basically we cut off arms and watch them grow it back. But, seriously, we actually know how they do it, which is you cut off the arm, or they lose an arm - somebody eats their arm, something like that - the cells that are left behind have the ability to go back to what they were doing back when they were in the embryo.

SEABROOK: So, they become stem cells sort of?

Mr. GARDINER: Yeah. I mean, it's an equivalent of that. So you look at a salamander, you cut off its arm and it grows back and you go, wow, that's great, you know, it can do it, we can't. And so we have the sense that we can't regenerate and that's not true. We can regenerate the epidermis on our skin and our bone regenerates and nerves can regenerate, blood vessels can regenerate.

But we don't seem to be able to coordinate that into making a complex structure that contains muscles and bones and skeleton.

SEABROOK: So, have you put your finger on a conductor in the salamander?

Mr. GARDINER: Yes. On a salamander these are the cells that make up what we call the connective tissue. These are actually the cells that allow us to hold together. But then a salamander are the ones that have information about where, you know, what's the top of our hand and the bottom of our hand and the tips of our fingers and our shoulder.

I mean, there's a reason that we look the way that we do. And these are the cells that have kind of the blueprint. So in the salamander they're the ones who control regeneration but in a human - we have these same cells - but they have a different response to injury, and these are the cells that make scars. And so that's really what we're focused on is that a salamander isn't making a scar.

So it's as if there's two different ways things can go in response to injury. You can either make a scar or you can regenerate.

SEABROOK: Cool. That's really cool.

Mr. GARDINER: Yeah, it is. It's actually pretty exciting.

SEABROOK: Does that mean that with your research as a basis we may not have the problem of missing arms and legs anymore? We may be able to regrow arms and legs and even organs and things?

Mr. GARDINER: Well, I'd like to think that. This much I do know: eventually we will be able to do that. The evidence is overwhelming that there will be a time - it's unclear when that time will be - that we'll, in fact, we have this intrinsic regenerative ability; we will figure out how to tap into it and regulate it and we will be regrowing body parts, including organs - not just arms and legs.

SEABROOK: So, David Gardiner, why can't we humans do this?

Mr. GARDINER: Well, I think that is the important question, which is why have we not evolved the ability to regenerate? And you have to assume that it's because there's something else about regenerating that is really, in an evolutionary sense, was not adapting.

So regeneration is obviously adapting. If you lose an arm, obviously it would be a great advantage to be ale to grow it back. But not if something else happens that kills you long before you have the opportunity to grow the arm back.

SEABROOK: Right.

Mr. GARDINER: That arm won't do you any good. And so our thinking about that is, is it almost certainly has to do with wound healing. Salamanders heal their wounds very differently than a mammal does. They do it very rapidly, there's very little bleeding. If you cut off the arm in a mammal, you know, the animal would bleed to death within minutes.

So it's something like that. And then if it raises issues about how we respond to infection. And so I think you can make the case for why it would be very hard for a mammal in the wild during the course of evolution to evolve the ability to regenerate.

And in fact, what they do is we have to close our wounds in a way that prevents us from dying from infection and bleeding to death. But in doing that it probably doesn't allow us to regenerate.

SEABROOK: David Gardiner is a research biologist at the University of California Irvine. Thanks very much.

Mr. GARDINER: Well, it was a pleasure. Thank you very much. Transcript provided by NPR, Copyright National Public Radio.