GENTECH archive 8.96-97

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Adult sheep cloned



Scientists clone adult mammal

By Malcolm Ritter, Associated Press, 2/23/97

NEW YORK (AP) - Researchers have cloned an adult mammal for the first time,
an astonishing scientific landmark that raises the unsettling possibility
of making copies of people.

Scientists slipped genes from a 6-year-old ewe into unfertilized eggs and
used them to try to create pregnancies in other sheep. The result: A lamb
named Dolly, born in July, that is a genetic copy of the ewe.

The feat opens the door to cloning prized farm animals such as cattle, and
should make it much easier to add or modify genes in livestock, experts
said.

It's also scientifically stunning. Researchers used DNA from the ewe's
udder cells, proving that mature mammal cells specialized for something
other than reproduction could be used to regenerate an entire animal.

Scientists had thought that was impossible.

Experts said the same technique might make it possible to clone humans, but
emphasized that it would be unethical to try.

``There is no clinical reason why you would do this. Why would you make
another human being?'' said Ian Wilmut, one of the scientists who cloned
the sheep. ``We think it would be ethically unacceptable and certainly
would not want to be involved in that project.''

Carl Feldbaum, president of the Biotechnology Industry Organization, which
represents about 700 companies and research centers in the United States
and abroad, agreed.

``I can think of no ethical reason to apply this technique to human beings,
if in fact it can be applied,'' he said Sunday.

``The biotechnology industry exists to use genetic information to cure
disease and improve agriculture. We opposed human cloning when it was a
theory. Now that it may be possible, we urge that it be prohibited by
law.''

A report of the sheep cloning will be published in Thursday's issue of the
journal Nature by Wilmut and colleagues at the Roslin Institute near
Edinburgh, Scotland, and others.

Before the new work, scientists had been able to take tissue from adult
frogs and create genetically identical tadpoles. But the tadpoles never
developed fully into frogs.

To do the sheep cloning, scientists took cells from the ewe's udder tissue
and cultivated them in a lab, using a treatment that made the cells
essentially dormant. They also took unfertilized sheep eggs and removed the
nucleus, the cells' central control room that contains the genes.

Then they put the udder cells together with the egg cells and used an
electric current to make them fuse. The eggs, now equipped with a nucleus,
grew into embryos as if they'd been fertilized. The embryos were put into
ewes to develop.

The process was horrendously inefficient. Of 277 fused eggs, only one led
to a lamb.

Wilmut said he expects the efficiency to improve. Someday a dairy farmer,
for example, might make a few clones of cows that are especially good at
producing milk, resisting disease and reproducing, he said.

A farmer wouldn't want entire herds of identical animals, because
populations need a diverse genetic makeup, he said. Without that diversity,
a lethal disease that struck one cow might wipe out all the clones, too.

The advance will also provide a much more efficient way to insert genes
into livestock, Wilmut and others said. Inserted genes can be used to make
animals secrete valuable drugs in their milk, for example.

Scientists currently insert genes into fertilized eggs in a laboratory,
which is a very inefficient way to produce animals that use the genes
properly.

With the new technique, they could start with a virtually unlimited supply
of body cells from an adult animal, use a much more effective lab technique
to insert genes, identify cells that use the genes as planned, and fuse
them to eggs.

Wilmut and colleagues published research last year that suggested this
technique could be done by inserting genes in embryo cells. But body cells
from an adult are far more plentiful than embryo cells, making the idea
more feasible.

Caird Rexroad Jr., an animal gene expert for the federal Agricultural
Research Service in Beltsville, Md., called the new work historic for
showing that whole mammals could be regenerated from mature-body cells
other than sperm or egg.