|Clones May Look Normal But Many Are Not
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|Author:||mesa_sound [ 07/05/01 01:30:00 PM ]|
WASHINGTON (Reuters) - Cloned mice created with embryonic stem cells may look normal but often have subtle abnormalities, scientists reported on Thursday, a finding that could lend support to those who oppose this kind of research.
Amid the intensifying U.S. debate over whether to use embryonic stem cells to look for cures for such diseases as Parkinson's and diabetes, researchers found that these cells might carry unexpected risks when used to reproduce organisms -- like cloned mice.
``The simplistic warning is clearly you can make cloned animals with problems (with embryonic stem cells); whether this will apply to other donor cell types remains to be seen,'' David Humphreys of the Whitehead Institute for Biomedical Research in Massachusetts said in a telephone interview.
But he added, ``We certainly don't want to discourage embryonic stem cell research in any way as a result of this.''
Stem cells are early cells not yet specifically earmarked to become any one part of the body, so they can develop into most any kind of cell the body needs, and as a result can be used in so-called reproductive cloning.
Opponents of research using human embryonic stem cells contend that adult stem cells are just as useful and present no moral problems. Some opponents of embryonic stem cell research see it as killing human life.
Those who support it point to possible advances for sufferers of such diseases as diabetes and Parkinson's and maintain that the human embryonic cells used for this research -- the products of in-vitro fertilization slated for destruction -- would never develop into human beings anyway.
EFFICIENT EMBRYONIC STEM CELLS
Humphreys said scientists often choose embryonic stem cells because they are more efficient in the cloning process.
In reproductive cloning, scientists remove the nucleus of an egg and replace it with the nucleus from either an adult cell or an embryonic stem cell. Ideally, the egg resets the developmental clock of the nucleus back to a state compatible with early embryonic growth; this is thought to happen more readily with embryonic stem cells than with adult cells that are already committed to a specific function.
``Throughout pregnancy, you find if you use embryonic stem cells as nuclear donors that you have a higher percentage of mice at least making it to birth,'' Humphreys said. ``It's also easy to imagine that using embryonic stem cells as donors might be easier to reprogram back to a state compatible with a fertilized egg.''
But even so, many of the cloned mice created in research at the Whitehead Institute and the University of Hawaii developed abnormally, even though they made it through pregnancy, birth and in some cases to adulthood.
The problem did not lie in the cloning process, but rather in the makeup of the embryonic stem cells, which were found to be extremely unstable in laboratory cultures.
The genes themselves were not at fault. However, the embryonic stem cells lost the tags that were supposed to tell the genes whether to turn on or off during development, the researchers found.
This meant that two mice cloned from the ``sister'' embryonic stem cells might have differences in the way their genes were expressed.
The research was published in the latest edition of the journal Science.
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