While the experiments involved mice, the work is being met with excitement - and questions - about doing the same thing for humans someday.

"Wow. That's my general reaction," said Hank Greely, a bioethicist at Stanford University who studies stem-cell science. "Repairing hearts, repairing brains, repairing kidneys, that's all good and important, and we'd all love to be able to do that. But this involves making the next generation."

Scientists obtain the versatile cells from embryos. Embryonic stem cells are controversial because researchers destroy the embryos to get them.

But because these stem cells can morph into any cell in the body, there's always been the possibility they could do something especially profound. They could offer a way to create eggs from anyone at any age. That could change how humans reproduce.

In this week's issue of the journal Science, Mitinori Saitou and colleagues at Kyoto University in Japan report they finally achieved that elusive goal.

"This is actually the first time to make eggs from embryonic stem cells and then produce eggs [that] become healthy offspring," Saitou said.

Moreover, Saitou's team did something potentially even more astonishing: They bred healthy mice from eggs made from another type of stem cell known as induced pluripotent stem cells.

These are cells that look essentially identical to embryonic stem cells. But instead of coming from embryos, they can be made from adult cells, such as skin or blood cells. So they don't have any of the ethical baggage of embryonic cells.

"They're gotten to what was our Holy Grail, which is making eggs," said George Daly, a leading stem-cell scientist at Harvard. "It's like cellular alchemy. I mean, they can turn lead into gold here. They can turn skin cells or blood cells into eggs."

The big question, of course, is whether anyone could do the same thing for people. No one knows for sure. And it would surely take a ton of work.

But John Gearhart, a stem-cell pioneer at the University of Pennsylvania, says mice are close enough to humans to think it's probably doable. "I think this will be worked out in time. I don't have any doubt about it," Gearhart said.

And if he's right, then, at the very least, it would be a huge advance for women who are infertile for medical reasons or who have postponed having babies too long.

"If we can make eggs from stem cells, then the biological clock isn't ticking so much for women," Stanford's Greely said.

But that could be just the beginning. The same team previously made sperm from stem cells. snip end quote

Which is pretty cool, I think.

I'm kind of reminded of the world of pet breeding... and how unorthodox and irresponsible and greedy it's all become...

-Ron-