Amid occasional controversial claims that cloned babies are well on their way to birth, researchers have published a study showing that in cloned mice, defects can be found throughout the genome. They say the work adds to evidence that cloning to produce a baby is unsafe and unethical.
Recent research has already demonstrated a number of abnormalities in cloned mice and other species, including obesity, pneumonia, liver failure, and premature death (ScienceNOW, 11 February); most cloned oocytes never make it through gestation. Some scientists say these symptoms may only be the tip of the iceberg. They say it would be a mistake to judge just from its appearance and behavior that a clone--such as the cute kitty born last spring at Texas A&M University (ScienceNOW, 14 February)--is normal. Rather, a detailed molecular analysis is needed.
A team led by biologist Rudolf Jaenisch of the Massachusetts Institute of Technology's Whitehead Institute in Cambridge did such an analysis with two types of cloned mice. One group was born from eggs whose nuclei had been replaced with genetic matter from a type of cell called a cumulus cell that surrounds the ovaries. The other group was created by implanting eggs with nuclei from embryonic stem cells--the as-yet-undifferentiated cells of very early embryos. After the animals were born, the team analyzed the expression of 10,000 genes in their placentas and livers. For both groups, up to 4% of the genes were malfunctioning: They were expressed at either more than twice or less than half their normal levels, the group reports online 9 September in the Proceedings of the National Academy of Sciences. "Cloned humans should have similar problems and most if not all would be expected to be abnormal," says Jaenisch.
The work "now gives us a more scientific basis" to question cloning, says Hans Schöler, a molecular biologist at the University of Pennsylvania School of Veterinary Medicine in Kennett Square, who earlier this year reported that most clones have a defect in a major gene involved in development. "Before, we were just saying that on the basis of [fewer than a dozen] genes that things might go wrong." Hundreds have now been added to the list--and that's for the successful clones that make it to birth. For the vast majority that never get that far, "you don't know how many genes were messed up," observes Schöler.