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Rats Born From Mouse Surrogate Fathers

Sperm developed in testes of different species, researchers report

MONDAY, Aug. 28, 2006 (HealthDay News) -- Rat sperm implanted into mouse testes have been used to fertilize rat eggs and produce healthy rat offspring, according to new research out of Japan.

The implications for human fertility, if any, remain unclear. But the study opens the intriguing possibility of cross-species assisted reproduction, something the researchers say might someday aid in the conservation of endangered species.

"As a pure research effort, it is very impressive," said Steven L'Hernault, a professor of biology at Emory University in Atlanta, who was not involved in the study.

The finding is the culmination of a decade of research that began when sperm cells from one animal species appeared to develop normally after being transplanted into another species.

The new study shows that such sperm cells are functionally normal, said a group led by Takashi Shinohara at Kyoto University.

In the experiment, the researchers collected sperm from mice that had been implanted with rat sperm cells. Those sperm were then injected into rat eggs, and the fertilized eggs were implanted in surrogate rat mothers. A total of 339 such eggs were transferred, and 90 managed to implant in the uterus, resulting in 15 successful births.

All the rats born in the trial had no observable abnormalities, and all were themselves fertile, the researchers reported.

"What this shows is that you can break the species barrier and still get functional sperm," L'Hernault said.

The findings were published in this week's issue of the Proceedings of the National Academy of Sciences.

What the Japanese scientists did is similar to the technique used in human fertility clinics, where sperm are commonly injected into eggs, L'Hernault said. But comparisons to human reproduction are limited in this case, he said, because "a lot of the genetic tools available in the [laboratory] mouse are not available in humans," he said.

More information

For more on human infertility, visit the American Society of Reproductive Medicine.

SOURCES: Steven L'Hearnault, Ph.D, professor, biology, Emory University, Atlanta; Aug. 28-Sept. 1, 2006, Proceedings of the National Academy of Sciences
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