Cloning chip

January 30, 2002

A CHIP that will automatically create hundreds of cloned embryos at a time is being developed by a Californian biotech company, New Scientist has learned.

If it lives up to its promise, the chip should help make cloning cheap and easy enough for companies to mass-produce identical copies of the best milk or meat producing animals for farmers. It might even be used for cloning human embryos.

The chip automates the laborious process of nuclear transfer, the key step in cloning. At present it takes hours of painstaking work with a microscope to remove the nucleus of an egg cell and replace it by fusing the denucleated egg with another cell.

"If somebody's got something like that, obviously it would make everybody's life easier," says Tanja Dominko of Advanced Cell Technology, the Massachusetts company that caused a stir late last year when it announced that it had created cloned human embryos.

In animals, cloning is still very wasteful. At best, around half of cloned embryos develop to the point where they can be implanted, and only a tenth of these survive to birth. Often more than a hundred nuclear transfers must be carried out to create a single clone.

Scientists usually start with a batch of 150 eggs, and denucleate them one at a time before moving on to the next step. That means eggs can be left sitting around for several hours, a delay that may reduce success rates.

But the nuclear transfer array developed at Aegen Biosciences, by the company's founders Richard Kuo and Gregory Baxter, could handle hundreds or even thousands of eggs at once. Kuo says they can routinely denucleate 30 to 50 sea urchin eggs at a time. They plan to start testing cow eggs in the next few weeks.

The prototype is a thin silicon slice a few centimetres across etched with hundreds of tiny wells, one for each egg. The trick is to spin the chip in a centrifuge, forcing the eggs' dense nuclei through a small hole at the bottom of each well. About 90 per cent of the eggs can be successfully denucleated this way, Kuo says.

Kuo and Baxter are now working on the next step, which is to fuse a donor cell with the denucleated egg. A lid with appropriately positioned donor cells will be placed on top of the eggs. "Then they're ready to fuse," says Kuo, although he won't reveal details of the method. After fusion, eggs that develop far enough could be implanted manually into an animal's womb as normal.

"If it works with cow [eggs], that would be very neat," says Rudolph Jaenisch of MIT, who studies problems with cloning. But just because it works with sea urchins doesn't guarantee that it will work with the eggs of other species, he warns.

And Randall Prather of the University of Missouri, whose team recently announced the cloning of miniature pigs, says the chip won't help solve other problems, such as ensuring that the eggs you use have been kept in the right conditions. He thinks it might also be too expensive for many labs.

Kuo admits there is much work still to be done on the chip, but he believes it's worth the effort. One could submit different batches of eggs to various treatments, to find out which conditions improve success rates in cloning, he says. Such studies could also help researchers identify the factors in eggs that reprogram the added nucleus.

If the chip does improve success rates in animals, it is likely to be used to create cloned human embryos, where the problem is not dealing with many eggs at a time but getting hold of sufficient numbers of eggs. Companies such as Advanced Cell Technology hope to obtain embryonic stem cells from cloned embryos but have had only limited success (New Scientist, 1 December 2001, p 4).

The chips might also appeal to the mavericks who want to carry out human reproductive cloning despite all the warnings about the risks. The warnings are based on the health problems seen in the few clones that do survive, which have also prompted the FDA to ask companies not to sell food from clones until it has been proved to be safe.
-end-
Author: Sylvia Pagan Westphal, Boston

New Scientist issue: 2nd February 2002

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New Scientist

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