Cloned mice make long-awaited debut.

The rumors were true. The brave-new world of cloning now includes mice.

After gossip about their work had circulated for months (SN: 7/11/98, p. 21), scientists from the University of Hawaii in Honolulu have finally confirmed that they have cloned a mouse--actually, about 50 of them--from cells of adult animals. In the July 23 Nature, Teruhiko Wakayama and his colleagues describe their technique, which differs slightly from the method used to clone the sheep Dolly.

As in the making of Dolly, the researchers removed DNA from an egg cell. However, instead of fusing an entire adult cell to the DNA-free egg--as Dolly's creators had--the Honolulu team merely injected the nucleus from an adult mouse cell into the egg. They allowed the transplanted DNA to sit inside the egg for several hours before treating the egg with a chemical that, prompts the cell to start dividing into an embryo. Through this technique, the investigators have created dozens of mice, including clones of clones.

Since Dolly's birth, scientists have speculated that mice, and perhaps humans, might be impossible to clone because of the speed with which their developing embryos turn on genes (SN: 4/5/97, p. 214). Cloning depends upon the egg returning the adult cell's DNA to an embryonic state, but that reprogramming was suspected to require more time than the embryonic development of some species allowed. "Given that so many of us failed [to clone mice from adult cells], it is not immediately clear why Wakayama et al. have succeeded," notes Davor Solter of the Max Planck Institute for Immunology in Freiburg, Germany, in an accompanying Nature commentary.

While inevitably reigniting the debate over the cloning of humans, this success in mice, the most common laboratory animals, should also speed research into the many mysteries still surrounding the working of this artificial reproductive method. The researchers, for example, were able to clone mice using nuclei from cumulus cells, which surround a growing egg in the ovary; attempts to clone mice from several other cell types, such as brain cells, failed.

Two additional reports in the same issue of Nature also contain news about Dolly that should dispel doubts about her heritage. Some scientists had questioned the evidence establishing that Dolly was cloned from an udder cell of an adult sheep. Two new analyses of Dolly's DNA, one conducted by the research group that cloned her and another by an independent team, now concur that it's almost impossible that the sheep is not a clone. These reports "have shown that Dolly is indeed the direct descendant of an udder cell from a nameless Finn Dorset ewe," says Solter.