Japanese female fish in sperm-producing strangeness

Researchers identify vertebrates' germ cells genetic switch

Japanese fish boffins have discovered – for the first time in vertebrates – a genetic switch which determines whether germ cells (essentially reproductive precursors) become either eggs or sperm.

The gene has been named fox13 and has been identified using a small fish called medaka, also known as the Japanese rice fish due to its proliferation in paddies.

The report on sex determination, titled "fox13 is a germ cell-intrinsic factor involved in sperm-egg fate decision in medaka", and published in Science, was written by Japanese fish and sex boffins.

The boffins discovered that in medaka without this gene's functionality, female fish produce healthy sperm in their ovaries, producing genetically normal offspring.

Female medaka lacking the functional genes are still wholly female, producing a small number of eggs.

It's also become clear, announced the Japanese National Institute for Basic Biology's press release, that in these females which were lacking the function of foxl3, functional sperm could be obtained in a shorter period of time than in normal wild-type males.

"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," Dr. Toshiya Nishimura, from the laboratory of Dr Minoru Tanaka, at NIBB, said.

Tanaka also offered that "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."

The abstract to the report explains that "sex determination is an essential step in the commitment of a germ cell to a sperm or egg. However, the intrinsic factors that determine the sexual fate of vertebrate germ cells are unknown".

Applied research into the uses of this information for aquaculture, and the farming of aquatic flora and fauna, is already underway. ®

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