Genetic Switch Choosing Sperm Or Egg Formation Found

A gene that controls whether the reproductive precursor cells known as germ cells eventually become sperm or eggs has been found by researchers in Japan.

The scientists reported experiments involving the Japanese rice fish, a small fish called the medaka, that showed the role of a gene called foxl3 in controlling the germ cells’ fate.

The exact same gene is not present in humans, but the researchers believe a similar genetic switch mechanism may play a role in our biology, too.

In medaka fish without this foxl3 functionality, sperm are produced in the ovaries of females. The sperm that are produced function normally, and have been verfied to result in normal offspring.

Also, in the females lacking foxl3, functional sperm can be obtained in a shorter period of time than in normal males. Research into application of the findings to aquaculture is already underway.

Reproductive biologist Dr. Toshiya Nishimura, of the National Institute for Basic Biology, said:

“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 finding.”

His colleague, associate professor Minoru Tanaka added:

“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.”

Toshiya Nishimura, Tetsuya Sato, Yasuhiro Yamamoto, Ikuko Watakabe, Yasuyuki Ohkawa, Mikita Suyama, Satoru Kobayashi, and Minoru Tanaka.
foxl3 is a germ cell-intrinsic factor involved in sperm-egg fate decision in medaka
Science DOI: 10.1126/science.aaa2657

Photo: Dr. Toshiya Nishimura is shown in an aquarium room at the National Institute for Basic Biology / Credit: National Institute for Basic Biology