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Cultured Eggs Could Defuse Stem Cell Politics
  
By Nancy Touchette

Scientists studying stem cells in mice have discovered a simple way to create mouse eggs from cultured stem cells. If this research can be applied to humans, it could eliminate the need to use human embryos as a source of stem cells and vastly defuse the controversy that goes with it.


Follicle-like structures derived from mouse embryonic stem cells.

Researchers at the University of Pennsylvania have developed an ingenious way to produce oöcytes, or egg precursor cells, from cultured embryonic stem cells in mice. They simply removed mouse stem cells from a layer of “feeder” cells on which they were growing and, to their surprise, discovered that these cells on their own had become mouse oöcytes.

If the technology is used for human cells, it could circumvent some of the political hurdles to human fertility research.

“If this can be transferred to humans, we could obtain oöcytes without getting people upset,” says Hans Schöler, who led the study, published today in Science.

“With this technique, we don’t need an embryo anymore for studying questions relating to fertility,” he adds.

Embryonic stem cells are cultured cells typically derived from embryos not used for in vitro fertilization treatments. Because they can become any type of cell, they are being actively studied for their potential in treating diseases like diabetes, Parkinson’s disease, and spinal cord injuries.

Schöler says the oöcytes separated from the clump of stem cells and floated away. He suspects that many researchers have generated oöcytes in culture, but have been unable to detect them. They tracked down the cells by inserting a gene that makes them turn green when they became oöcytes.

“If you have a dish with embryonic stem cells growing in it, you have no idea what you are looking at,” says Schöler. “We saw many green cells that behave just as germ cells behave in the embryo.” Early in the development of an embryo, germ cells such as egg and sperm migrate to the gonads.

“They move together like they are part of a caravan,” says Schöler. “But they detach from each other when they reach the gonads. In culture they round up and float. Many researchers probably thought these cells were dead and not worth investigating.”

The researchers showed that the oöcytes they produced were stimulated in a process known as parthogenesis to develop to an early embryonic stage. They are now investigating whether the eggs can be fertilized by sperm to form viable embryos.

Schöler will use the new system to study how a nucleus from a mature cell is reprogrammed when transferred into an egg. The genes that are activated in a mature cell are different than those activated in an embryo. To reprogram the genome, certain genes must be turned off, while others are turned on.

“We are trying to understand the mammalian oöcyte because it has everything required to reprogram a nucleus,” says Schöler. “Sperm are boring compared to what is going on in the oöcyte.”

See related GNN articles
»Bone Marrow Heals the Heart
»Stem Cell Therapies: Time to Step Back or Forge Ahead?
»Stem Cell Alert: Laws and Players

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Hübner, K. et al. Derivation of oocytes from mouse embryonic stem cells. Science, published online May 2, 2003.
 
Read, T-A. et al. Local endostatin treatment of gliomas administered by microencapsulated producer cells. Nature Biotechnology 19, 29-34 (January 2001).
 

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