Clone telomeres behave normally Early embryo telomerase-
dependent length resetting means clones won't have short
telomeres By Cathy Holding
A team of researchers at Hannover Medical School, Germany,
has found a telomerase-dependent telomere length-resetting
event between the morula and blastocyst embryonic stages
that they say keeps cloned embryo telomere length normal.
Because telomeres-the structures located at the end of chromosomes-
lose a piece of their sequences with each cell division,
short telomeres are usually correlated with age, said Heiner
Niemann, professor and head of the Department of
Biotechnology at the Institut für Tierzucht, Neustadt,
Germany, who coauthored the study, published in the May 17
PNAS Early Edition, with Sonja Schaetzlein and colleagues.
Scientists had earlier looked at telomere lengths in cloned
animals because there was some concern that such animals may
exhibit premature aging. "There was quite an uproar with
Dolly [the first sheep clone] in that when they measured
telomere length, they were indeed obviously shortened
compared to age-matched controls," Niemann said. However,
later studies in cloned cattle and mice showed telomeres to
be of normal length, he said.
The Hannover researchers compared lengths of telomeres in
bovine donor nuclei and recipient cells. They then carried
out nuclear transfer and analyzed telomere lengths at the
morula and blastocyst stages in clones and in vitro-
fertilized embryos. In the morula, cells are compact and
mostly the same type, while the fluid-filled blastocyst
comprises two different cell lines: the trophoblastic
line, which later on forms the placenta, and the inner
cell mass, from which the embryo proper is derived,
Niemann said. "So [the morula-blastocyst transition] is a
very critical stage."
Read the rest at The Scientist.com
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