| The
cells of cloned mice show no signs of premature aging despite
being copied through six generations, according to a new
study. In fact, some of the cells showed signs of getting
younger.
The
study published in Thursday's issue of the journal Nature
contradicts a 1999 study of Dolly the cloned sheep that
showed the protective tips of her chromosomes, known as
telomeres, were showing signs of early wear and tear because
they were copied from genetic material that was 6 years
old.
Many
questions surround how telomeres behave in the cells of
cloned animals. Not only might cloned animals die prematurely,
but healthy cloned cells created as medical treatments
might die off before they can fight disease.
Cells
can divide a certain number of times before they die —
about 70 times for humans and fewer for other mammals.
Every time a cell divides, the telomere is whittled down,
but the genetic material remains intact. Eventually the
telomere is too short to protect the genes and the cell
soon dies.
The
mouse study conducted at the University of Hawaii and
Rockefeller University in New York cloned six successive
generations of mice in a row. Researchers said the telomeres
of some mice were longer than expected, even in mice that
lived for more than one year.
``Our
results verify that telomere shortening is not a necessary
outcome of the cloning process,'' said the study's lead
researcher, Teruhiko Wakayama.
Wakayama
said he could not explain why the cloned mice had long
telomeres.
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