Sperm Cells Turned into Eggs

Scientists have tricked male fish cells that were destined to become sperm into switching sex and becoming eggs instead.

The technique could one day be used to quickly produce animals with desired traits, speed up breeding programs and help repopulate dwindling populations of endangered species or creating sushi on demand, the researchers said.

The finding is detailed in the Feb. 7 issue of the journal for the Proceedings of the National Academy of Sciences.

Sexually indifferent cells

Scientists have long known that some fish are able to switch their sex, either spontaneously or when exposed to steroids. This led them to suspect that a subset of the population of cells in male fish that normally become sperm, called spermatogonia, might be stem cells that have the potential to become either sperm or eggs.

To test their hypothesis, the researchers isolated spermatogonia from the testes of adult rainbow trout and transplanted them into newly hatched trout of both sexes. In male hatchlings, the transplanted cells developed into sperm, while in females they developed into eggs.

The scientists are currently looking into whether eggs could be transformed into sperm. Other researchers have successfully produced sperm from mice stem cells.

Sushi on demand

The technique could be used to rapidly breed inbred strains of domestic or research animals with desired genetic traits, the researchers write.

Tokyo University's Goro Yoshizaki, the study's principal investigator, told LiveScience the technique could be used to establish surrogate breeding programs for animals such as the blue fin tuna, a fish popular for sushi and sashimi in Japan and elsewhere. Populations of the fish are declining worldwide and adult blue fin tunas are expensive and difficult to keep in captivity.

One solution, Yoshizaki said, is to isolate the spermatogonia from adult male tunas and transplant them into both male and female hatchlings of a smaller fish species, such as mackerel. Once transplanted, the germ cells would differentiate into sperm and eggs. The mackerel would then be allowed to reproduce normally, but they would produce tuna instead of mackerel.

The technique could also be used to help save endangered fish species, Yoshizaki added. A single male endangered fish could be used to repopulate an entire species.

"Even if the species is extinct, we can restore them by transplanting them into closely related species," Yoshizaki said.

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