Mice produce sperm of pigs and goats

Lab experiment hints of future applications for livestock, cancer patients

August 15, 2002|By Michael Stroh | Michael Stroh,SUN STAFF

Will the stork one day be joined by the mouse in the baby business?

A team of American and German scientists has for the first time coaxed mice into producing the sperm of distantly related barnyard animals.

The research, described today in the British journal Nature, raises hope that the technique might someday provide new options for everyone from cancer patients rendered infertile by chemotherapy to zookeepers trying to bring back endangered species.

During the past decade, scientists have successfully transplanted sperm-producing cells from rodents such as rats and hamsters into mice, which then began producing sperm from the donor animal.

But sperm-cell transplants into mice from more evolutionarily distant animals - such as dogs, pigs, bulls, horses and primates - have all flopped.

In the experiment published today, Ina Dobrinski at the University of Pennsylvania and colleagues at the University of Munster took a different tack.

In addition to sperm-producing cells, scientists also sliced out some surrounding tissue from the testicles of newborn pigs and goats.

Each pinhead-sized sample was implanted under the back skin of mice that had been castrated and specially bred to deactivate their immune system, which might have rejected the transplanted tissue.

Most tissue survives

More than 60 percent of the transplanted tissue samples survived and eventually began generating healthy sperm.

"Those grafts produced as much sperm, gram for gram, as testes in the donor species," Dobrinski says.

The scientists are unsure exactly why this experiment worked when earlier attempts had failed. Sperm production in mammals is a complex and still largely mysterious process, notes Dobrinski.

Scientists do know it's very temperature sensitive. And researchers speculate that a mouse's back offers the perfect environment. "Under the skin it was just about right," she says.

Sperm production also requires a cocktail of hormones to trigger the process. Dobrinski says she and her colleagues were surprised that the mice produced the right kinds in the right quantities to jump-start the process in testicular tissue taken from such distantly related animals.

Roger Gosden, scientific director at the Jones Institute for Reproductive Medicine in Norfolk, Va., says the research is an important step forward. But he cautions: "It remains to be seen what uses it's going to be put to."

If experiments with human tissue also prove successful, there could be a wide range of applications, Dobrinski says.

Unlike cryogenically frozen sperm deposited in a sperm bank - which once used up is gone for good - the transplanted tissue offers a potentially inexhaustible supply.

The transplant technique could be especially beneficial to pre-pubescent boys with cancer, since their testes are not mature enough to produce sperm for banking.

Preserving their tissue elsewhere - such as in the back of a mouse - might be a valuable option, scientists say.

Dobrinski, a veterinarian at Penn's School of Veterinary Medicine, said the technique might also be used to help preserve endangered species or to quickly breed prized bulls or champion racehorses.

In the experiments, the researchers found transplanted testicular tissue produced sperm weeks faster than it would naturally in the donor animals, making it possible for scientists to breed new generations of animals more quickly than they otherwise could.

Catch-up research

The mouse experiment is one of several unusual experiments carried out by fertility scientists in the past year. And researchers working on sperm and the testes are playing catch-up to their colleagues who have been studying female reproductive organs.

Cornell University researchers reported last fall, for example, that they implanted tissue from women's ovaries into the patients' own forearms. Nine weeks after tissue was implanted, scientists noticed signs that the tissue was producing eggs.

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