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First 'genetic switch' found in vertebrates determines which cells become sperm, eggs

A gene that determines the fate of germ cells, no matter the sex of the host, has been discovered using fish.

By Marilyn Malara
Young medaka born using normal eggs and sperm from female fish lacking functional foxl3 genes. Photo by National Institute for Basic Biology
Young medaka born using normal eggs and sperm from female fish lacking functional foxl3 genes. Photo by National Institute for Basic Biology

WASHINGTON, June 13 (UPI) -- Researchers in Japan have found a gene that determines whether germ cells become sperm or eggs. Named foxI3, the gene was identified using small Japanese fish called medaka.

When without this specific gene's functionality, female medaka produced healthy, seemingly normal sperm in their ovaries and autonomously produced their own offspring. Although they looked female outwardly, the fish created copious amounts of their own sperm and a small amount of eggs in their reproductive tracts.

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"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," co-author Dr. Toshiya Nishimura said in a press release.

Co-author Dr. Minoru Tanaka said, "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," he said.

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The National Institute of Basic Biology says research on how to apply these findings for aquaculture -- the rearing of aquatic plants and animals for consumption -- is already underway. The research was published in the journal Science on June 11.

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