|
By Sylvia Pagán Westphal
A Californian biotech company is developing a chip that will automatically
create hundreds of cloned embryos at a time.
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.
Urchin
Eggs
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, could handle hundreds or even thousands
of eggs at once. 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 centimeters 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.
Scientists 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. After fusion, eggs that develop
far enough could be implanted manually into an animal's womb as normal.
Too Expensive
If it works with cow eggs,
that would be very neat. But just because it works with sea urchins doesn't
guarantee that it will work with the eggs of other species.
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.
There is much work still to
be done on the chip. 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.
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.
New Scientist January
30, 2002
| 