Researchers in Japan successfully created mouse egg cells from stem cells by adding vitamin A and protein, making progress toward technology that may be useful in human fertility treatment, a study published in a European science journal showed Tuesday.

So far, egg cells, or eggs before maturation, have been created by cultivating mouse embryonic stem cells together with somatic cells of the ovary. But the team of researchers led by Kyoto University professor Michinori Saito made egg cells without the somatic cells.

The egg cells need to undergo a further process to become eggs, such as transplanting them into the ovary or cultivating them with somatic cells. Saito's team said it also wants to create eggs without relying on those steps.

"If we can apply this to human beings, it can be helpful for fertility treatment," Saito said.

In the study shown in the online journal of the European Molecular Biology Laboratory, the researchers first made germ cells from mouse embryonic stem cells, which can make any other cell in the body.

They then put the germ cells at culture plates with vitamin A and protein that induces the formation of bone for about a week and developed egg cells with a probability of more than 90 percent.