At Stanford, stem cells shed light on human development

SAN JOSE, Calif. — Stanford University researchers have fabricated the cells that make sperm and eggs, the components of human reproduction, shedding light on a little-understood stage of early human development and offering hope for infertility, genetic disease and prevention of birth defects.

Through a complex and delicate process, the research team nudged embryonic stem cells to grow up a little, maturing into the so-called "germ cells" that are more fundamental to conception than candlelight and soft music.

The team doesn't want to build a baby. Rather, they plan to study the early steps of human development, when events sometimes go terribly awry and create disease.

They also hope that lab-produced sperm and eggs could someday help people who can't make their own and are thus unable to conceive. If these sperm and eggs are functional, they could be used for in-vitro fertilization.

"Human development is a very complex process, and we've never had a system before to study it in the lab, to see the things we can see now," said lead investigator Renee Reijo Pera, who directs Stanford's Center for Human Embryonic Stem Cell Research and Education Center. The research was published in Wednesday's issue of the journal Nature.

Embryonic stem cells are versatile building blocks that, given the right conditions, can be induced to morph into a variety of more mature cells. In leading labs around the country, they've turned into tissue types such as neurons, muscle and the lining of the gut.

The new work, which builds on previous research involving genes linked to infertility, is funded in part by the California Institute for Regenerative Medicine, created by passage of Proposition 71 in 2004. Embryos were donated by families undergoing in vitro fertilization.

Previous research yielded only immature versions of these reproductive germ cells. The Stanford team went further, inducing these cells to go all the way through the reductional process of meiosis so the cells contain just one copy of a chromosome, a critical step in sexual reproduction.

The germ cells even made immature sperm, called spermatids.

The next step is to try to produce oocytes, the eggs made by women.

"It is a very nice paper. I think it is particularly important to show the production of haploid cells," like spermatid, "that have one copy of each chromosome, not two," said Dr. Arnold Kriegstein, director of the Eli and Edythe Broad Center of Regeneration Medicine and Stem Cell Research at the University of California-San Francisco.

"I think it provides a road map for how to explore a complicated process like meiosis," said Kriegstein. "Problems with fertility may be due to problems with these processes."