Researchers in Japan have identified a gene that controls whether germ cells become sperm or eggs. The experiments involved a fish called the medaka, or Japanese rice fish, that revealed the role of a gene called foxl3. Reuters reports:
Germ cells are present in the bodies of vertebrates of both sexes, but the molecular mechanism that drives them to develop into either sperm, the male reproductive cell, or an egg, the female reproductive cell, has been elusive.
In determining that foxl3 serves as a genetic switch for deciding the sperm-or-egg question, the researchers found that the gene is primarily active in a female's germ cells to prevent them from becoming sperm cells instead of egg cells in the ovaries.
The gene is not active in the surrounding cells of the fish's reproductive organs.
When the scientists inactivated the gene in female fish, the germ cells turned into sperm in the medaka's ovaries rather than eggs cells, as might be expected in a female. Those sperm cells functioned normally, successfully fertilized egg cells and produced healthy offspring.
Humans do not possess the exact same gene, but the researchers suspect a similar genetic switch mechanism may be at play in people, too.
"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," Minoru Tanaka of the National Institutes of Natural Sciences in Japan said.
