Genetic switch decides sperm or egg formation

Japanese researchers have found for the first time in vertebrates a genetic switch that determines whether germ cells become sperm or eggs.

The gene has been identified using a small fish called medaka (Oryzias latipes) in which, surprisingly, sperm are produced in the ovaries of females without this gene's functionality.

The sperm that are produced function normally, and have been confirmed to produce normal offspring.

"In spite of the environment surrounding the germ cells being female, the fact that functional sperm has been made surprised me greatly. That this sexual switch present in the germ cells is independent of the body's sex is an entirely new result," said Dr Toshiya Nishimura from National Institutes of Natural Sciences.

While germ cells can become either sperm or eggs, nobody knew that in vertebrates the germ cells have a switch mechanism to decide their own sperm or egg fate.

"Our result indicates that once the decision is made the germ cells have the ability to go all the way to the end. I believe it is of very large significance that this mechanism has been found," said Nishimura.

The results are forthcoming in the journal Science.