Cloning - The Science (video) - Cloning could one day cure
diseases like Parkinsonâ€™s, diabetes and even heart disease.
But it could also be used to make a copy of a human being. (10/31/02)
Cloning - The Ethics (video) - The United States bars government-funded
scientists from cloning human cells to cure diseases. But the
nation has not outlawed cloning a human being. (10/31/02)
Elsewhere on the web
Cloning Ban Delayed
Of The Clones: Fresh Warnings About Replication" - SpaceDaily.com
cloning cheap and easy - New Scientist
Are clones normal? It's a serious question now that there's a growing industry
in cloning animals, and claims that a human clone is coming soon.
This ScienCentral News story investigates why cloning experts are far from
Jaenisch: Expression Errors
When a normally fertilized embryo develops, genes are turned on and off in
a precise sequence. The genes specify the production of proteins that build
each type of body cell, and build those into tissues and organs. They also
code for the proteins that turn genes on and off, regulating the whole complex
process. This protein-making is called gene
Cloning expert Rudolf
Jaenisch says the process of normal reproduction begins long before fertilization,
as the egg and sperm develop into cells designed by evolution to combine and
make a baby.
"Egg maturation is a process which takes decades in women for example,
and sperm maturation months," says Jaenisch, a founding member of the
at MIT. "But this very complex process assures that the two gametes,
the mature sperm and the mature egg, that they're in a state that their genes
can now activate the correct way when they come together at fertilization,
to direct development of a new organism."
Cloning circumvents this process. To make a clone (see Human
Cloning - The Science), you remove the nucleus from an egg cell, and replace
it with a nucleus from an adult body (somatic) cell, a technique called somatic
cell nuclear transfer.
"The genes in a somatic donor cell—let's say in the mammary gland cell,
which gave rise to Dolly—those genes in those cells are expressed for the
normal physiology of a mammary gland cell, let's say to give milk," Jaenisch
explains. "But the genes which are important for embryonic development
are there, but they're silent. They're not expressed."
Somehow, somatic cell nuclear transfer causes the resulting cell to be reprogrammed
to act like a fertilized embryo. This reprogramming is not very well understood,
but Jaenisch says one can't expect it to happen exactly as it does in normal
"So the problem is really, you asked this somatic nucleus, let's say the
one from the mammary gland, to do something in very short time, maybe hours,
what normally occurs in egg and sperm maturation in months or years."
"You can't expect that this would work," says Jaenisch. "I am
totally surprised that it works even sometimes and you get an adult animal."
To support this, Jaenisch cites two types of evidence:
Gene expression: Jaenisch's lab analyzed the genomes of cloned mice and
found that many genes are not correctly expressed. The research
was published in Proceedings of the National Academy of Sciences.
Watching clones age: He says that while these gene expression abnormalities
might not be apparent in young clones, they reveal themselves as the animals
age. "When we look at aged cloned animals, you only can do that in
mice because cloned cows are just very young for cow ages. If you look
at cloned aged mice, it turns out that all of those die earlier, significantly
earlier than controls, with major abnormalities in many, many organs."
Jaenisch has become a leading advocate against cloning a human being, and his
argument against it is cited by many scientists who oppose reproductive cloning
West: Don't Trash Cloning
West also opposes cloning humans. But he couldn't disagree more on whether
it works. "I would have to say that the cloning of human beings is probably
entirely possible to do," he says.
"I've never bought the argument of some of my fellow scientists that we
ought to, you know, in a sense trash cloning to try to prevent some out of
control people from cloning human beings," he says [see Human
Cloning— the Ethics].
West's company, Advanced
Cell Technology, has cloned dozens of prized meat and dairy cattle, some
now five years old and still apparently healthy.
"The realities are, we can clone animals safely and the animals are healthy
for the most part," West says.
West says cloning is a useful technique that is well on its way to being practical
Last year, Advanced Cell scientists published
a paper in the journal Science
that evaluated 30 cattle that were cloned from adult body cells. They
said 80 percent were alive and healthy from one to four years after birth.
Another major cloning company, Infigen,
claims that it has studied more than 120 cloned cattle and more than 50
cloned pigs, and that they are normal.
The scientists are critical of each otherâ€™s evidence. Jaenisch says Advanced
Cell's criteria were superficial because they conducted physical examinations
and blood tests, but did not investigate the clones at the level of gene expression.
West says of Jaenisch's study, "It is true that there's abnormalities
in some of the placentas, the tissue that allows the developing animal to
be fed from the uterus, but not in the body of the animal itself."
"At this point," says West, "we have scientists disagreeing
with one another."
Are the companies that have invested in cloning biased? West suggests that
maybe they are better at cloning. West says "popular reports" that
"there are hundreds and hundreds of attempts to clone with one successful
result" are "largely a myth."
While not disclosing any numbers on Advanced Cell's cloning efficiency, West
says it is steadily increasing. "It's not as efficient as normal reproduction,
but we are steadily approaching that level of efficiency," he says.
"Should that mean we should clone humans?" West asks. "I think
not, and the reason is, in the case of humans, we're far more valuable, and
a mistake made, an abnormal human being, carries a far greater price than
an abnormal mouse. And so until we know it's safe to clone a human being—absolutely
know—I think we shouldn't even begin the experiment of trying to clone a