A CHIP that will automatically create hundreds of cloned embryos at a time is
being developed by a Californian biotech company, 快猫短视频 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.
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鈥淚f somebody鈥檚 got something like that, obviously it would make everybody鈥檚
life easier,鈥� 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.
快猫短视频s 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鈥檚 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鈥� 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. 鈥淭hen they鈥檙e ready to fuse,鈥� says Kuo,
although he won鈥檛 reveal details of the method. After fusion, eggs that develop
far enough could be implanted manually into an animal鈥檚 womb as normal.
鈥淚f it works with cow [eggs], that would be very neat,鈥� says Rudolph Jaenisch
of MIT, who studies problems with cloning. But just because it works with sea
urchins doesn鈥檛 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鈥檛 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鈥檚 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
(快猫短视频, 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.