Since 1997, when Dolly the sheep became the first animal cloned from an adult cell, evidence has been mounting that cloning creates problems. For example, cloned cows have faulty immune systems, and cloned mice grow obese and exhibit other abnormalities. Now a group in Japan has shown for the first time that clones die younger than animals created by old-fashioned sexual reproduction.
A team in the laboratory of Atsuo Ogura at the National Institute of Infectious Diseases in Shinjuku, Tokyo, cloned 12 mice by removing nuclei from testis cells and inserting them into enucleated egg cells. They compared these mice to a genetically similar group created by natural mating. The cloned mice started dying off at the age of 311 days--about half the age the normal mice began their decline, the group reports in the 11 February online version of Nature Genetics. By 800 days, 10 of the 12 clones were dead, whereas about 80% of the normal mice were still alive. Postmortem exams of six cloned mice revealed that they all had severe pneumonia. Four also had extensive liver necrosis, and two had cancer--leukemia in one case, lung cancer in the other.
The authors say their study offers further evidence that clones are likely to have a variety of impairments. It also suggests that the type of impairments clones experience may depend on what kind of body cells are used as donor cells. Unlike previous mice created with the nuclei of cumulus cells--cells that surround and nourish eggs--the mice that Ogura's group used did not become obese.
All these problems suggest that in cloning, the donor nucleus is not properly reprogrammed to resemble that of a freshly fertilized egg, says developmental biologist Davor Solter of the Max Planck Institute for Immunobiology in Freiburg, Germany. The chances that "one lucky clone will by accident have all its genes correctly reprogrammed," he says, are minuscule.