Mouse Stem Cells Grow Into Eggs

Without using any special chemicals or growth stimulants, researchers at the University of Pennsylvania said that stem cells from mouse embryos would transform into oocytes, or eggs, and then into primitive embryos.

'Most scientists have thought it impossible to grow gametes from stem cells outside the body,' said Hans R. Scholer of the school of veterinary medicine at the University of Pennsylvania. He said his team found that not only can the stem cells transform into eggs, but those cells then form embryos.

However the embryos could not be used for reproduction as they contain an incomplete set of chromosomes, but the eggs probably could be used for cloning.

Embryonic stem cells can grow into virtually any cell in the body. Some researchers have suggested they could be used to grow new heart, liver, brain or pancreas cells which then could be used to revive or repair ailing organs.

To make these new organ cells compatible with a patient, researchers say they would have to clone an embryo using the nucleus from a cell of the patient. At an early stage of development, the new stem cells would be removed and then grown into the target cells.

The process kills the embryo, and there would have to be a large supply of human eggs for this technique to ever be medically useful for the millions of people who could benefit. Right now, those are only available from women donors who undergo a painful harvesting procedure.

The study by Dr. Scholer and his co-authors suggests that eggs could be made in the laboratory from stem cells. This would avoid the need for donors -- addressing one of the ethical concerns about using human embryonic stem cells for medical treatment -- and lead to an almost limitless supply.

In the study, Dr. Scholer and his co-authors put into stem cells a gene that would prompt a glow from a fluorescent marker if the cells begin turning into egg cells.

After few days, the cells transforming toward eggs cells formed clumps and then individual cells coated with follicle-like cells similar to the tissue surrounding normal eggs in female mammals. In a process that resembled ovulation, said Scholer, the oocytes were released by the follicle cells on day 26.

The oocytes then went on to form embryos in a process called parthenogenesis, or reproduction without sperm fertilization. Dr. Scholer said that such embryos generally are not viable, but he believes the eggs may be normal.