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Monday, Feb. 11, 2002
Scientists in Tokyo find that cloned mice have shorter lives
By ROWAN HOOPER
Scientists at the National Institute of Infectious Diseases in Tokyo have found that cloned mice have shorter life spans than mice conceived naturally.
With Dolly the sheep, the first cloned mammal, suffering from premature arthritis, and previous studies showing that cloned animals tend to be obese and may have higher rates of immune dysfunction, the Japanese study will add to worries about the long-term effects of cloning.
Published online today in Nature Genetics, the work is the first to link cloning with premature death.
Atsuo Ogura and colleagues examined 12 mice cloned from immature cells in the testis. The cloned mice started to die after 311 days, with 10 of the 12 dying before 800 days. Only one of seven naturally conceived mice died before 800 days.
An examination of six of the clones revealed severe pneumonia and liver failure, which was not observed in the normal mice raised under controlled experimental conditions. As antibody production in the cloned mice was reduced, the authors suggest that the immune systems of the mice may not be able to fight off infection.
The authors caution that the factors affecting clone longevity are many and subtle, including genetic background and the type of cell from which the nucleus is taken -- the so-called donor cell.
"There may be reprogramming error," said Ogura in an e-mail interview, "which may have unpredictable effects in the long run."
Reprogramming error is thought to occur when a cell already assigned to a bodily task -- in this case in the testis -- is "reset" in preparation for cloning and development into an embryo.
"This study reinforces the opinion expressed by many that clones are not entirely normal and that we should be careful about how we use this technology," said David Solter, a biologist at the Max Planck Institute of Immunobiology in Freiburg, Germany, who was not involved in the Japanese study.
"We are continuing tests on the immune system of cloned mice using other genotypes (mouse strains)," Ogura said.
"We have increased the number of parameters and animals examined. We will obtain additional results within the year."
Ogura stressed that public concern about cloning should be guided by science. "In this context, we think that our study provides a scientific basis for public concern about human reproductive cloning."