New method to create mature egg cells discovered

Immature mouse eggs have been successfully matured and fertilised in the laboratory for the first time. Eggs from women undergoing cancer therapy were also successfully matured using the new method, offering hope for some women suffering infertility such as cancer patients made infertile by treatment.

Until now, fertility treatments have matured eggs at a relatively late stage in development when they are less numerous and harder to access. But the new method, termed 'in vitro activation' (IVA) stimulates ovarian follicles - the structures encasing immature egg cells - earlier when they are still dormant.

Professor Aaron Hsueh, senior author of the study, said the technique: 'holds the promise of expanding the options for women seeking treatment for infertility', particularly those who have no or too few eggs.

To generate the mature eggs, an ovary from three-day-old mice was treated with a chemical inhibitor of PTEN - an enzyme which keeps the early follicles in an inactive state - along with 740Y-P, an activating substance. After two days, most of the follicles were activated. The follicles were transferred to adult mice and follicle stimulating hormone (FSH) was given daily.

Two weeks later, the treated ovaries were visibly larger, heavier and contained up to six times more advanced follicles than the untreated ones. Twenty healthy mouse pups were born after the mature eggs were fertilised and 118 embryos transplanted into adult female mice.

The same PTEN-blocking chemical was used to treat immature eggs in human ovarian tissue, which was transplanted into host mice. After six months, the tissue contained a much higher percentage of advanced follicles or mature eggs than the untreated tissues. But the human eggs weren't fertilised and the authors were careful to point out much more work is required before the technique can be used in humans.

The researchers, led by Dr Jing Li at Stanford University, California, published their findings online in the journal Proceedings of the National Academy of Sciences (PNAS). The study was funded by National Institutes of Health (NIH).