Researchers: Cloned mice die young
Report in science journal may cast doubt on safety of cloning
WASHINGTON, Feb. 10 — Japanese researchers who cloned a dozen mice reported Sunday that virtually all of the animals died early. The researchers’ comments preceded a report to be published Monday, a report that specialists said was sure to be taken as evidence that cloning people should be banned.
THE REPORT, published in the Feb. 11 issue of the journal Nature Genetics, also suggested that the technique used to clone an animal can have an impact on its ability to live a normal life span, cloning experts said.
“The possible negative long-term effects of cloning, as well as the high incidence of spontaneous abortion and abnormal birth of cloned animals, give cause for concern about attempts to clone humans for reproductive purposes,” said Atsuo Ogura and his colleagues at the National Institute of Infectious Diseases in Tokyo.
Congress is considering several bills intended to ban human cloning. Two would allow research to continue so long as no baby was created using the technology, and a third would ban the use of all cloning technology to make a human embryo.
Experts at the National Academy of Sciences, which advises the government, have also said cloning is too uncertain to use as a method for making babies, although the report leaves open the possibility of doing so in the future if the technique is perfected.
Labs that have cloned animals have reported that the cattle, sheep and goats that make it to adulthood are normal in every way that can be measured.
One big glitch has been in Dolly, the sheep that was the first mammal cloned from an adult in 1997. She has developed early arthritis, which her creators say could be either bad luck or a result of the cloning process.
SHORT LIVES FOR MICE
Ogura’s team reported on 12 male mice they cloned that looked normal at birth, although certain liver enzymes, used to monitor liver activity, were abnormal.
“The cloned mice started to die 311 days after birth, and 10 of the 12 cloned mice died before 800 days,” they wrote. Mice born through natural mating and conceived using artificial fertilization lived much longer. The mice had abnormal livers, lungs and perhaps some immune-system anomalies, Ogura’s team reported.
Two of the clones are still alive and might live normal lives. It might be that the genetic makeup of the clone’s “parent” is key to healthy survival, they said.
They also noted that clones may be born “old.” Some clones have shortened telomeres, which are a kind of cap on the chromosome, the structures that carry the genes. Each time a cell replicates, this telomere cap frays a little; this process is believed to be associated with aging.
TECHNIQUE MAY MATTER
Technique could also be important, said Tony Perry of Advanced Cell Technology in Worcester, Mass., one of the companies trying to use cloning technology to make human embryos for medical uses. Perry, who was part of the first group to clone mice, said the method is different from the method used to make larger animals, such as Dolly.
Dolly was created using electrofusion. One sheep’s egg had the nucleus taken out, and a cell from the mammary gland of another adult sheep was fused to it using a burst of electricity. The second cell’s nucleus and its genetic material replaced the missing nucleus, and the egg grew and divided as if it had been fertilized by a sperm.
EMBRYO DAMAGE THEORIZED
To make mice, the Japanese team micro-injected the nucleus from the second cell into the egg. “This method is rather different,” Perry said in a telephone interview.
One method might somehow damage the tiny embryo, Perry and a colleague, Teruhiko Wakayama, said in a commentary on the study.
Or it could that be the cytoplasm, the part of the cell outside the nucleus, carries key factors for survival that are transferred with the electrofusion method.
Perry also noted that not all adult cloned animals were normal, and that most clones died at or before birth.