More MS news articles for Jan 2002

Study suggests reason for type of cloning problem

Jan 10, 2002
By Amy Norton
NEW YORK, (Reuters Health)

A certain type of genetic defect that has been seen in cloned animals may be due to the cells used in the studies, and not the cloning procedure itself, researchers in Japan report.

To clone an animal, scientists remove the nucleus from an egg and replace it with the nucleus of a cell from the "donor" that is to be cloned. In many experiments in cloning mice, researchers have gotten the donor nuclei from embryonic stem cells. In other attempts at animal cloning, such as the creation of Dolly the sheep, adult or fetal cells have been used.

Animal cloning is a complicated process, and it only occasionally results in a birth. There have also been concerns about genetic anomalies occurring in surviving clones. Just last week, Dolly was reported to have arthritis, raising concerns that the cloning process exacted a genetic defect.

Among the problems that can occur are anomalies in imprinted genes, which play a key role in growth and development. Imprinted genes differ from other genes in that their expression in the body depends on whether they came from the father or mother. Some research has shown that mice cloned from embryonic stem cells can have abnormalities in their expression of imprinted genes.

In the new study, reported in the January 11th issue of Science, scientists cloned mice using nuclei from adult somatic cells--cells other than egg or sperm. The investigators found that the embryos, fetuses and full-term animals they created were no more likely than normal mice to have faulty imprinted genes.

The findings suggest that the cloning procedure itself is not to blame for past imprinted-gene abnormalities in mice, according to Atsuo Ogura of the National Institute of Infectious Diseases in Tokyo, Japan, and colleagues.

Instead, Ogura told Reuters Health, the problem may have arisen from mutations that accumulated in the donor embryonic stem cells during the process of culturing them.

Cloning procedures have garnered much interest because scientists hope to use them in treating disease. Unlike reproductive cloning, such therapeutic cloning would involve creating new cells and tissue to replace those damaged by disease. Scientists do not foresee using embryonic stem cells as donors in therapeutic cloning, Ogura's team points out.

Still, Ogura said, it is also possible that other potential donor cells, when cultured for long periods, could develop genetic abnormalities.

This might be avoided, the researcher said, by being particularly careful about the cells' culturing conditions. In this study, Ogura's team used "freshly prepared" donor cells.

However, the investigators looked only at problems with imprinted genes. Ogura noted that scientists will have to keep studying cloned animals to confirm that other genetic mechanisms are normally maintained.

SOURCE: Science 2002;295:297.

Copyright © 2002 Reuters Limited