Mice Cloned From Cultured Stem Cells

In an experiment that joins the booming fields of stem cells and cloning, scientists have managed to clone mice from embryonic stem cells. The report is the first demonstration that long-established cell lines could be used to clone animals--offering researchers the possibility of cloning mice directly from genetically manipulated cells.

Although researchers have cloned numerous cows, sheep, goats, and mice, most were cloned from relatively fresh cells that had not spent much time in a lab dish. Dolly's genetic material, for example, was taken from one of her mother's udder cells. The reason is that although cells in culture are easy to work with, they often accumulate mutations. Those mutations can throw a wrench into embryo development, so scientists were unsure whether long-cultured cell lines would be candidates for cloning.

That didn't faze reproductive biologist Teruhiko Wakayama. Working in the lab of Ryuzo Yanagimachi of the University of Hawaii, Honolulu, Wakayama and his colleagues experimented with two embryonic stem (ES) cell lines that had each gone through more than 30 cell divisions in culture. Using the same technique that first enabled them to clone mice last year, they carefully extracted a nucleus from an ES cell and transferred it into an enucleated mouse egg. The cultured cells developed into healthy embryos about as well as cells from a living animal do, the team reports in tomorrow's Proceedings of the National Academy of Sciences.

Cloning researchers aren't on easy street yet, however. Other experts note that, like all cloning so far, the procedure is very inefficient. The team transferred more than a thousand nuclei to obtain 13 mice that survived to adulthood, points out developmental biologist Davor Solter of the Max Planck Institute for Immunology in Freiburg, Germany. And although other labs have tried, no one else has reported cloning a mouse. Still, if scientists could boost the technique's efficiency and use it to go directly from a genetically manipulated cell to a live animal, "that would be fantastic," says embryologist Brigid Hogan of Vanderbilt University in Nashville, Tennessee.