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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