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FEBRUARY 24, 1997TRANSCRIPT |
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Scientists have cloned an adult mammal for the first time, producing a lamb named Dolly. The lamb was cloned from a 6-year-old ewe, using tissue taken from the ewe's udder. The study, to be released in this week's Nature, has raised questions over the possible uses, and ethical dilemmas, of this development. Following a background report and discussion of the science of today's announcement, Jim Lehrer leads a discussion of the ethics of cloning.
NEWSHOUR LINKS:
A RealAudio version of of this segment is available.
February 24, 1997:
A background report on the cloning of sheep in Scotland.
February 24, 1997:
A discussion on the ethics of genetic engineering.
March 7, 1997:
Join an Online NewsHour forum debating the merits of cloning mammals.
April 3, 1996:
Fred De Sam Lazaro reports on scientific advances in genetic research and the ethical questions they raise.
EXTERNAL LINKS:
The Genetics and Public Issues Program at The National Center for Genome Resources (NCGR) discusses cloning.
Discussion of Ethics and Social Issues in Gene Research at the Human Genome Project.
ELIZABETH FARNSWORTH: Now we'll get an explanation of the cloning story from two people who've been watching it closely. Randall Prather is a professor of animal science at the University of Missouri, who is currently doing research on early embryonic development in pigs. And Paul Raeburn is a senior editor at BusinessWeek who recently authored The Last Harvest, a book about cloning animals. Thank you both for being with us.
Mr. Raeburn, is this an important scientific breakthrough?
PAUL RAEBURN, BusinessWeek: (New York) It's a fascinating story. I think it's important on at least three levels. It's a fascinating piece of basic science. This is something that was supposed to have been impossible. Researchers thought that adult cells could not be used to produce new animals. That's No. 1. No. 2, it has, as you've already mentioned, enormous implications, practical applications could lead to all kinds of things, new drugs, growing animal organs for transplants, and No. 3, I think it's--it's clear to all of us that this has tremendous mythic significance. I mean, this is just a very, very big step in making it a realistic possibility that one might think about cloning a human being.
ELIZABETH FARNSWORTH: We're going get into some of that much later, a little bit later in the show, but, Mr. Prather, I want to ask you--researchers had come fairly close to this before, right?
RANDALL PRATHER, University of Missouri: (Jefferson City, MO) Yes, they have. Some of the procedures that we developed while I was at University of Wisconsin-Madison in the lab with Dr. Neil First were designed to attempt to clone embryos, not adults, but to take cells from early embryos and do the cloning procedures.
If I might add to the comments that were made a little bit ago, we also have potential production agriculture, pharmaceuticals. The applications also are for research. I think that's one thing that's often omitted here. If we can create cloned animals, then we can reduce the number of animals that are needed for experimentation because, as you know, when you do experiments, you have two treatments, and the reason you have more than two animals is because of genetic variation. And by being able to do these procedures and create genetically identical individuals, hopefully, we will be able to reduce the number of animals that are needed for experimentation.
ELIZABETH FARNSWORTH: Prof. Prather, let's back up a minute. I want to understand how this works. I may be old-fashioned, but I always thought you needed a sperm mixed with an egg to make the cell division occur that created an embryo. Explain how you can take DNA from an udder, put it into an egg from which the nucleus has been removed, and get life.
RANDALL PRATHER: Well, in essence, the DNA in the nucleus in the udder has both the male and the female contribution because the ewe has both a mother and a father. So that genetic compatibility that's necessary is already there. The other thing that you have to do when you do the nuclear transfer is to fuse the cells. Well, when you fuse the donor cell--in this case the mammary cell with the recipient egg--you also have to trick that egg. You have to make--
ELIZABETH FARNSWORTH: Okay. Back up one minute. Fuse. Just go back one minute. What do you mean by fuse? That's where the electricity comes in, right?
RANDALL PRATHER: Yes.
ELIZABETH FARNSWORTH: Explain that.
RANDALL PRATHER: The electric pulse does two things. One thing is it causes a transient membrane breakdown in both the donor cell and the recipient cell. When the membrane re-heals, oftentimes there are small pores that remain. These pores are thermodynamically unstable. And what will happen is those pores will enlarge just fusing the two cells together. The electric pulse does another thing. It poreates the cells such that calcium that's in the culture media can leak into the egg. That calcium leaking into the egg then mimics what the sperm does at fertilization. Abnormal fertilization, the sperm fuses with the egg, there's a huge calcium release within the egg, and so by using the electric pulse, they're able to mimic that.
ELIZABETH FARNSWORTH: Then they put the egg back into the ewe.
RANDALL PRATHER: That's correct.
ELIZABETH FARNSWORTH: And only one out of thirteen actually became pregnant. Is that--do you have any idea why that happened?
RANDALL PRATHER: Well, when we first began working on nuclear transfer, we did probably a thousand nuclear transfers before we got our first couple of calves. And that was using early embryonic cells, cells that haven'd grown through gestation and haven't produced an adult animal. And we did a lot of ‘em, and basically what that tells you is, No. 1, the procedure works. It's highly inefficient. What we really need is more research to understand exactly how it's working and why it doesn't work most of the time but why it does work part of the time, so procedures do become more efficient.
ELIZABETH FARNSWORTH: Paul Raeburn, why didn't somebody try this before?
PAUL RAEBURN: Well, I think there was a feeling that adult cells were irreversibly changed. What happens, as you may know, in a very early embryo after the egg has divided several times, it's possible to take any one of those cells, separate it, and put it in another womb, and it can grow into another animal, another human being, if that's the case. So at a very early stage each cell has the potential to grow into the whole animal; however, as development continues, the cells lose that ability, and adult cells are believed to be, or at least were believed to be pretty much locked into their role. A liver cell was a liver cell and a skin cell was a skin cell. Now we've shown that a mammary cell can be induced to regain what it was thought--what had been thought to be irreversibly lost, that ability to regenerate and help a new egg grow into a new animal.
ELIZABETH FARNSWORTH: And, Mr. Raeburn, if you can do this to an animal, can you do it to a human?
PAUL RAEBURN: If you can do it to a sheep, you can do it to a human being. There may be technical problems and minor difficulties. As you noted, there were 277 eggs fertilized and put into 13 lambs to get one. That might be 2,000 it takes to get one human, or it may be simpler. But in principle, if it can be done in one mammal, it can be done in another.
ELIZABETH FARNSWORTH: Randall Prather, how difficult is this process after reading the Nature article? Is it something you could do in your lab?
RANDALL PRATHER: Could I do it in my lab? If--we do have the expertise, and if we had the funding and the facilities, we could probably repeat the work, yes.
ELIZABETH FARNSWORTH: So it's not terribly difficult, the technology? RANDALL PRATHER: I wouldn't say terribly difficult, but it does take a certain amount of expertise.
ELIZABETH FARNSWORTH: And Prof. Prather, in the introductory piece before our discussion, Dr. Wilmut mentioned some of the applications, and you all have mentioned others. How would cloning lead to an animal-producing useful medicine? How does that work?
RANDALL PRATHER: Well, really the next step in this process is to take those mammary epithelial cells and transect them, in other words, put in a gene of interest. If you're working with the pharmaceuticals, put in the gene that will make that pharmaceutical, select those cells that really have the gene in, functioning the way you want it to, and then use those for nuclear transfer.
ELIZABETH FARNSWORTH: In other words, you take the DNA from the udders, the mammary cells, and you just put the other kinds of genes in there that you want in there?
RANDALL PRATHER: Yes.
ELIZABETH FARNSWORTH: Is that right?
RANDALL PRATHER: That's one logical next step, yes.
ELIZABETH FARNSWORTH: So then that's not really a clone because you've added some different kinds of genes? You're fiddling with it then?
RANDALL PRATHER: That's true.
ELIZABETH FARNSWORTH: That is the scientific application. And Mr.--go ahead, sorry.
RANDALL PRATHER: That is one application, yes.
ELIZABETH FARNSWORTH: That is one application. And Mr. Raeburn, how about--how would it work? How would pig clones be engineered to make them good sources of organs for humans?
PAUL RAEBURN: Well, when a pig organ is transplanted into a human being, or as they remember the famous story, the baboon hearts, there's a ferocious immune reaction that kills off that invading organ. What this breakthrough would enable researchers to do would be to produce a pig in which the--its normal immune system signals had been replaced by the human counterparts, so then when the organ is grown, it's still a pig heart or a pig liver, but all the signals on it that the immune system recognizes are human. So it would be recognized as a human organ when it was transplanted, which would make it feasible to do those kinds of transplants.
ELIZABETH FARNSWORTH: Mr. Prather, do you have anything to add to that? You're working with pigs.
ELIZABETH FARNSWORTH: So this may be very useful for your work, this cloning?
RANDALL PRATHER: Yes, but I'm not going to change my whole lab direction. We have some specific objectives that we're working on and working towards very successfully, and we'll probably incorporate this. In fact, over the last couple of weeks we've set up a collaboration with Dr. Mark Westsuzen, and Dr. Jorge Piedraita at Texas, and to be able to do this specific procedure with pigs.
ELIZABETH FARNSWORTH: And how does it work? How does the cloning help with cures for genetic diseases, or is it pretty much what you've already explained?
RANDALL PRATHER: Well, it's pretty much what I've already explained. The cures really come about by understanding the basic science, and understanding the basic science is easier if the genetics are equal between the two animals that you're working on.
ELIZABETH FARNSWORTH: Explain that.
RANDALL PRATHER: Well, if we create genetically identical animals and we do an experiment and we can test in both animals two different treatments, then we can get a good comparison of how the animal's responding, and so that these procedures will help us to understand that better.
ELIZABETH FARNSWORTH: And, Mr. Raeburn, overall, what do you think is the most important of the applications?
PAUL RAEBURN: Well, I think the basic science will lead to all kinds of new things that may be difficult to anticipate right now. But it--you know, it does set up the perfect nature-nurture kind of experiment to look at the effects of environment on animals. If you have two animals that are genetically identical and change their environments, there's no telling what kinds of things we might learn. So I think over the short-term drugs, organ transplants -- over the medium-term; and over the long-term it's hard to say but I think tremendous advances.
ELIZABETH FARNSWORTH: Thank you both very much for being with us.
PAUL RAEBURN: Thank you.
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