CLONING CANNOT WITHER?
Researchers have repeatedly cloned six generations of mice, in each case taking genetic material from somatic cells of the previous cloned generation. The results offer some surprising new insights into ageing, Teruhiko Wakayama, of the University of Hawaii, Honolulu, and colleagues report in a Brief Communication this week in Nature [VOL. 407 NO. 6802 DATED 21 SEPTEMBER 2000, pp. 318–319].
The protective structures called ‘telomeres’ at the ends of the animals’ chromosomes, which are usually whittled away by cell division (of which there is an excess in a cloned animal), appeared to lengthen slightly; this is not in line with some studies that had predicted telomere shortening.
In Wakayama’s small-scale study, the mice seemed mentally and physically normal — a fifth-generation cloned mouse is alive and well in the rodent equivalent of middle age. But the difficulty of yielding clones increased with each generation, and the experiment was brought to a halt when the single sixth-generation mouse was eaten by her foster mother.
"Any deleterious effects of cloning might be expected to be amplified in sequentially cloned mice," says Wakayama’s group. "Our results verify that telomere shortening is not a necessary outcome of the cloning process." But the researchers do concede that, since only 1 to 2% of reconstructed eggs yield live clones, "the possibility of selection for donor nuclei with the longest telomeres cannot be excluded."
To date, researchers have cloned a number of large and small animals by nuclear transfer, including sheep, goats, mice and cows. But the jury is still out on the important question of whether genetic changes in the cells used to obtain nuclei may lead to adverse effects on the health of clones.
Teruhiko Wakayama (currently at Rockefeller University, New York)
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(C) Nature press release.
Message posted by: Trevor M. D'Souza