Of Mice and . . . More Mice

In 1996, Dolly the Sheep became the first creature ever cloned by science. Now, years later, geneticists have made yet another breakthrough. Using stem cells, a team of researchers at Japan’s Kyoto University were successful in creating the first artificial egg and sperm—of a mouse. Even more astounding, the fertilized egg actually produced offspring. Normal, healthy mouse pups can now be created in a petri dish, more or less.

The stem cells used are known as embryonic stem (ES) cells and induced pluripotent stem (PS) cells. ES cells are taken from embryos, and PS cells are adult tissues that are reprogrammed to act like stem cells. Both are capable of reproducing the body’s myriad cell types, at least in theory. In practice, however, researchers have been unsuccessful in their attempts to produce germ cells, “precursors of sperm and eggs.”

Now, a team of biologists, led by Mitinori Satou, have found a solution. Using a process they developed for creating sperm, they started with ES and PS cells. These cells were then cultured in a protein cocktail to produce cells similar to germ cells. The team then mixed these primordial cells with fetal ovarian cells, producing ovaries that were then “grafted onto natural ovaries in living mice.” Weeks later, the cells had developed into oocytes (germ cells). The ovaries were then removed, and the oocytes were fertilized and transferred to surrogate mothers. After three weeks, the mice gave birth to normal mouse pups.

“It is remarkable that one can produce oocytes capable of sustaining complete development starting with embryonic stem cells,” said developmental biologist David Solter. Amander Clark of the University of California believes that the work will impact how we understand the molecular process that forms germ cells. Saitou hopes that, with a bit more understanding, they may be able to “coax the cells through the entire oocyte development process in a lab dish.” If successful, they would be able to skip the grafting process entirely.

This advance could result in new treatments for infertility. It is “clinical proof,” says Clark, “that oocytes can be generated from . . . stem cells.” Moving on to human research will require resolving ethical and technical difficulties, Saitou warns. Solter believes that this approach could one day lead to “the production of human embryos” without the need for parents at all.

In the future, this research could help infertile couples, or it could be used to create “designer babies” for those who can afford them. Far darker possibilities can be easily conjured: human cloning, whole armies grown in a lab, a world where traditional notions of identity become a thing of the past. Only time will tell.