BioEd Online

From the 20th Annual Meeting of the European Society of Human Reproduction and Embryology, Berlin, Germany

Cells that are capable of making new eggs have been isolated from adult mouse ovaries. The finding supports an earlier suggestion that mammal ovaries could produce eggs throughout life, and shatters the dogma that women are born with a finite supply.

The researcher involved has even identified a molecule that boosts the activity of these cells and causes mice to develop twice as many egg follicles as normal. If it works in humans, such a chemical could provide a revolutionary treatment for women with a low egg-count, such as cancer survivors or those nearing menopause.

Jonathan Tilly from Harvard Medical School, Boston, who is behind the work, first hinted that adult mice might be able to grow new eggs earlier this year. In Nature, he reported seeing stem cells that were potentially able to develop into eggs within adult mouse ovaries¹1.

But he was unable to isolate the cells, so critics were not convinced. Now, Tilly has isolated the cells and shown that they display genetic markers that are characteristic of stem cells with the ability to develop into eggs. Although he will not disclose his method, he says he obtained 150 to 200 such cells from a single mouse ovary.

"It's an intriguing story," says Ursula Eichenlaub-Ritter from the University of Beilefeld, Germany, who studies ovarian development. But she cautions that the cells need to be characterized further before the case is proven.

Character building

Tilly has already started characterizing the cells. He has identified a gene in the mice that appears to regulate the stem cells' activity. When he knocked out this gene, the resulting mice had 40% more follicles in their ovaries than normal.

And he has even identified a molecule, which he calls GSA8, that has a similar effect. Tilly will not reveal the identity of GSA8. But he told this week's meeting of the European Society of Human Reproduction and Embryology in Berlin that when he injected it into female mice just before puberty, they ended up with almost double the normal number of follicles.

Tilly suspects that the same kind of mechanism could work in humans. "Why would Mother Nature put all her eggs in one basket when they would just sit there and accumulate DNA-related damage?" he asks. He points out that female flies, fish, birds and now mice all appear to make new eggs throughout life, so it is unlikely that humans would be any different.