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Japanese scientists grow stem cells into sperm cells

Posted on: Tuesday, 16 September 2003, 06:00 CDT

Japanese scientists grow stem cells into sperm cells

Experts a step closer to controlling reproduction

By RICK WEISS Washington Post

Tuesday, September 16, 2003

Scientists in Japan have transformed ordinary mouse embryo cells into sperm cells, marking the first time those specialized sex cells have been cultivated in the laboratory.

The achievement offers researchers an unprecedented window through which they can study the mysterious process by which embryo cells become sperm and brings scientists a step closer to controlling the basic mechanisms of sexual reproduction.

Scientists said the work would also advance efforts to engineer sperm with specific genetic traits -- a capability that, if applied to human embryonic stem cells and sperm, would pose new ethics questions regarding the extent to which people should be allowed to alter their genetic legacies.

The advance could eventually lead the way to new and controversial methods of reproduction. Scientists had already demonstrated that embryonic stem cells could be turned into eggs. By showing that these cells can also be driven to become sperm, scientists said, it now seems possible that baby mice -- and perhaps human babies as well -- could be created from nothing more than two laboratory-grown stem cells, one transformed into a sperm and the other into an egg.

"Basically, you could have human sexual reproduction without people," said Lee Silver, a professor at the Woodrow Wilson School of Public and International Affairs at Princeton University.

Embryonic stem cells are the "starter set" of cells inside every mammalian embryo that later differentiate into all the kinds of cells needed to make an adult body.

Scientists first isolated human embryonic stem cells just five years ago and have just begun to learn how to turn them into various cells -- to serve, for example, as replacement tissues and organs for patients with degenerative diseases. Stem cell research is more advanced in mice, because mouse embryonic stem cells were discovered more than 20 years ago.

Scientists generally agree that what can be done with mouse cells will also prove possible in human cells. But until this year it's been impossible to turn even mouse stem cells into eggs or sperm -- unique cells bearing half the standard complement of DNA.

In May, scientists at the University of Pennsylvania broke the first barrier by growing eggs from mouse embryonic stem cells, and made the surprising discovery that eggs could be made from either male or female stem cells. That discovery stirred visions of a strangely altered future in which gay men could have their own children through sexual reproduction, with one man providing sperm and the other providing eggs made from his own stem cells. (They would still need a woman to carry the resulting embryo and fetus to term.)

The newly announced creation of sperm from mouse stem cells does not raise the same gender-bending possibilities because sperm, it turns out, can be grown only from male embryonic stem cells. So even if the mouse feat gets replicated with human cells, lesbians would not have the capacity to make their own babies, since their stem cells won't grow into sperm.

Scientists said by taking sperm production out of the testes where it normally occurs, the new research makes it possible for scientists to watch the process unfold and, of perhaps greater interest and concern, manipulate it.

Scientists already know how to insert individual genes into stem cells, researchers noted. That means it should now be possible to grow sperm from stem cells that have been genetically altered, opening a new way to endow one's offspring with desired biological traits.

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