David Humpherys [1,2*], Kevin Eggan [1,2*], Hidenori Akutsu [3*], Konrad Hochedlinger , William M. Rideout III , Detlev Biniszkiewicz , Ryuzo Yanagimachi , and Rudolf Jaenisch [1,2], "Epigenetic Instability in ES Cells and Cloned Mice," Science, Vol. 293, No. 5527, pp. 95-97 (July 6, 2001).
Cloning by nuclear transfer (NT) is an inefficient process in which most clones die before
birth and survivors often display growth abnormalities. In an effort to correlate gene expression
with survival and fetal overgrowth, we have examined imprinted gene expression in both mice
cloned by nuclear transfer and in the Embryonic Stem (ES) cell donor populations from which
they were derived. The epigenetic state of the ES cell genome was found to be extremely
unstable. Similarly, variation in imprinted gene expression was observed in most cloned mice,
even in those derived from ES cells of the same subclone. Many of the animals survived to
adulthood despite widespread gene dysregulation, indicating that mammalian
development may be rather tolerant to epigenetic aberrations of the genome. These data imply
that even apparently normal cloned animals may have subtle abnormalities in gene expression.
1. Whitehead Institute for Biomedical Research
2. Department of Biology, Massachusetts Institute of Technology, 9 Cambridge Center, Cambridge MA 02142, USA
. 3. Department of Anatomy and Reproductive Biology, John A. Burns School of Medicine, University of Hawaii, Honolulu, HI 96822, USA.
* These authors contributed equally to this work.
To whom correspondence should be addressed. E-mail: firstname.lastname@example.org.
Cell Cloning Flawed
AP Science Writer
July 6, 2001; Washington, D.C. (AP) -- Researchers have found serious abnormalities in cloned mice, a finding that strengthens the belief of many scientists that the technique used to clone Dolly the sheep should not be used on humans. The findings are based on the use of embryonic stem cells in cloning and come as the Bush administration considers whether to allow federal funds for non-cloning stem cell research. The research appears today in the journal Science.
"This study confirms the suspicions of many of us that cloning of humans would be really dangerous," said Rudolf Jaenisch, senior author of the study and a researcher at the Whitehead Institute for Biomedical Research and MIT.
David Humpherys, first author of the study, said that many of the mice cloned in the experiment appeared to be normal, including having normal genes, but there was evidence that during embryonic and fetal development the genes did not work properly. "It is quite likely that just the animals that are most nearly normal make it to birth (in cloning), but our study shows that doesn't mean they are completely normal," said Humpherys. "There may be changes in gene expression that could affect them later in life."
In cloned humans, Jaenisch said the gene expression flaws could affect personality, intelligence, and other human attributes. Humpherys said there was no evidence that the genes in the cloned animals were altered, but that the way in which the genes made proteins was flawed and unstable. In effect, the researchers found that even though the biological blueprint was intact in the cloned animals, the way that the blueprint was read and interpreted was flawed. "This could result in abnormal tissues and organs," they said.
Humpherys and Jaenisch said that a number of scientists doing cloning experiments with mice, pigs, sheep, and cattle have reported that even apparently normal animals develop disorders later in life Jaenisch said that extreme obesity has developed in many cloned animals, including Dolly, the first mammal cloned from an adult cell.
Dr. David A. Prentice, an Indiana State University Professor of Life Sciences, said the MIT-Whitehead study shows the hazards of the current cloning technology. "Development is a finely orchestrated ballet of cells forming tissues and organs at the right place and time," said Prentice. "It takes only one going awry at the wrong time and place to have a seriously flawed individual."
In the study, the researchers made the mouse clones using embryonic stem cells, the primordial cells known to be able to form virtually any tissue in the body. The DNA from the cells was removed and inserted into a mouse egg that had been stripped of its DNA. The resulting embryos were then implanted in mother mice and allowed to grow to birth.
The researchers monitored the expression, or action, of genes that play a role in embryo and fetal development. They found that the genes, even from nearly identical stem cells, worked differently. "In fact," said Humpherys, "stem cells are unstable in gene expression even in the laboratory dish."
This instability raises the possibility that using stem cells to treat health disorders may not work as well as some scientists have suggested, said Dr. Joann A. Boughman, Vice President of the American Society of Human Genetics. "When we grow [embryonic stem] cells for a curative situation, we will need to control the process precisely," she said. "This paper shows that we've got a very long way to go to understand this whole process fully."
Some researchers have suggested that embryonic stem cells could be cloned from a patient and used to grow cells that could be used to restore that patient's ailing heart or liver or other organs. Jaenisch said that "it is unlikely that genetic instability would block the curative use of embryonic stem cells." He said "in developing cells for therapeutic use, researchers would harvest and inject into patients only those cells that are normal." "During cloning," he said, "no such selection is possible because an embryo must use the DNA provided and cannot select only that which is perfect."
Regulations that would permit Federal funding of embryonic stem cell research has been delayed by President Bush who ordered a review of the whole issue. Some members of Congress oppose embryonic stem cell research because obtaining the cells involves the death of a human embryo. Many scientists, however, believe that embryonic stem cell research could relieve suffering for millions of patients with a variety of disorders.
[ Editor's Note: Not mentioned in the AP article by Paul Recer above is another quotation attributed to the senior author... "Our findings should not alter the potential of [therapeutic] stem cell technology as a source of disease therapies. The problems discovered in the new research only arose when we forced the cloned embryos to develop into mature animals," said Dr. Jaenisch.[ Ref. Robert Lee Hotz, "More Doubt Cast on Cloning Safety," The Los Angeles Times, p. A26 (July 6, 2001).]
On the Web:
1. Science: www.eurekalert.org
2. Cloning: genomics.phrma.org/cloning.html
[ Editor's Note: Reference 2 above is an excellent resource for additional references on cloning research.]