Human 'cloning' makes embryonic stem cells
08 Oct BBC
A form of cloning has been used to create personalised embryonic stem
cells in humans, say researchers.
Genetic material was taken from an adult skin cell and transferred
into a human egg. This was grown to produce an early embryo.
Stem cells have huge potential in medicine as they can transform into
any other cell type in the body.
However, the stem cells formed contained chromosomes from both the
adult and the egg cells.
The technique used - somatic cell nuclear transfer - shot to fame in
1997 when Dolly the sheep, the first mammal to be cloned from an adult
cell, was unveiled to the world.
A South Korean scientist, Hwang Woo-suk, had claimed to have created
stem cells from cloned human embryos, but was found to have faked the
evidence.
The lead researcher at the New York Stem Cell Foundation Laboratory,
Dr Dieter Egli, said there was "a great question mark" about whether the
cloning technique could be reliably used in humans.
He said other "groups had tried before, but failed".
Writing in the journal Nature, he said his group had also failed
using traditional techniques.
When they removed the genetic material from the egg and replaced it
with the chromosomes from a skin cell, the egg divided but failed to go
past the 6-12 cell stage.
However, when they left the egg's own genetic material in place and
added the skin chromosomes, the egg developed. It reached the blastocyst
stage, which can contain up to 100 cells and is the usual source of
embryonic stem cells.
Eggs and sperm both have one set of chromosomes, which combined means
adults have two copies of each chromosome.
In this technique the two adult copies are added to the single copy
in the egg meaning a total of three, which can be problematic.
Often embryos without the correct number of chromosomes do not
develop at all. Down's syndrome is caused by three copies of just one
chromosome.
Researchers will need to produce embryonic cells which have only
donor DNA, however, once the egg starts to divide the chromosomes are
combined in the nucleus and would be near impossible to separate.
Dr Egli told the BBC: "The cells we have made are not yet for
therapeutic use. There is clearly more work to be done, this is early
days.
"We see this as a step on that road, so now we do know that a human
egg can turn an adult specialised cell, such as a skin cell, into a stem
cell."
Prof Mary Herbert, from the Institute for Ageing and Health at
Newcastle University, said: "This study shows that the conventional
approach to somatic cell nuclear transfer is inefficient in humans.
"However, the authors were able to increase the efficiency by leaving
the host oocyte [egg] genome in place.
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