Japanese researchers have discovered a genetic switch in fish (and maybe other vertebrates) that determines whether germ cells will become eggs or sperm. The gene has been called foxl3.
Germ cells, which are present only in reproductive organs, are the cells that are transformed into either sperm or egg cells. In males, sperm cells are formed while egg cells are formed in females. This study showed that foxl3 is one of the genes involved in determining whether sperm cells or eggs cells will be made.
The study was performed on a small species of fish known as medaka. The researchers found that foxl3 was primarily active in females where it, in part, caused germ cells to develop into egg cells. It is also responsible for preventing the formation of sperm cells in females.
To confirm that the gene does stop sperm production in females, they deactivated it in some female fish. This resulted in sperm production in females. The sperm that formed in the ovaries function normally and could be used to create healthy offspring. When the gene was switched off, there was no change in the female body; the only difference was that they produced sperm in addition to eggs.
The sperm produced by females is actually easier to obtain than from male fish so this discovery could have implications for commercial fishing when trying to increase populations.
Toshiya Nishimura, one of the researchers in the study said, “That this sexual switch present in the germ cells is independent of the body’s sex is an entirely new finding.”
“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,” said Minoru Tanaka, another researcher
The foxl3 gene is not found in humans according to researchers but they think there is a very similar mechanism regulating gamete production.
This new finding came as a surprise to researchers. Germ cells were always thought to be passive, relying on regulation from other cells so they were surprised to find it had a switch of its own. This study shows that germ cells are more dynamic than originally thought. This greatly increases the understanding of gamete production in vertebrates.
The study was published in the journal Science.