Mice Used as Sperm Factories for Pigs, Goats

Hillary Mayell
for National Geographic News
August 14, 2002
For the first time scientists have been able to produce viable sperm from the tissue of sexually immature mammals—and at the same time produce sperm of one species in the body of another species.

Researchers report that by transplanting tissue from the testicles of newborn pigs and goats onto the backs of laboratory mice the tissue not only survived but it started to produce mature, fully functional sperm of the donor species.

The ability to produce virtually unlimited amounts of sperm using this technique could conceivably be used to help human couples struggling with male fertility problems, preserve species close to extinction, and in animal husbandry.

Mouse-Grown Sperm

Earlier techniques using isolated germ cells worked only in closely related species of rats and mice. To overcome this problem, scientists at the University of Pennsylvania grafted fragments of testicular tissue taken from newborn pigs, goats, and mice onto the backs of nude mice. Testicles are the male reproductive gland, responsible for producing testosterone and sperm cells.

More than 60 percent of the grafts of all three species produced mature, fully functional sperm.

"The biggest challenge was to produce sperm from testis tissue that is sexually immature," said Ina Dobrinski, a veterinarian researcher at the University of Pennsylvania and co-author of the study published in the August 15 issue of the journal Nature.

"In an adult you can always save sperm, but say you have a boy child who is about to undergo chemotherapy. Using this technique you could save a little of the testis tissue to generate sperm when he is grown up. Before this, there was no option for the sexually immature individual."

The technique also has applications in animal husbandry. Livestock producers could use testicular tissue of genetically very valuable animals to generate sperm and perpetuate a breed or simply the bloodlines of animals possessing valued traits like the ability to produce a lot of milk or wool.

Preserving and enhancing populations of endangered species is another potential application for the technique.

"Zoo animals frequently have difficulty reaching maturity," said Dobrinski. "A lot of cat species are endangered. If you have ten male animals, but only five reach adulthood, you have a very small gene pool. This technique would allow us to produce sperm from all ten animals, thereby increasing the genetic variation within a population."

Sperm Factories Ethics

Producing sperm isn't the same as cloning, but reproductive research is a field strewn with ethical land mines.

"Now we know how to do this, but we don't know all the ramifications and consequences of doing it," said Bill Lynn, an animal and global ethicist at The Hastings Center, a research institute focused on ethical questions based in New York. "Infertility really tears at peoples hearts, but we need to proceed with caution and not rush into application."

The technique raises questions of whether diseases or genetic defects will jump from species to species. AIDS and ebola are two deadly examples of diseases that originated in primates and have been passed into the human population.

Zoonotic disease creates a disease effect for the child; a genetic, hereditable defect could be passed on and duplicated in the overall population, said Lynn.

"This question is particularly important among animal populations because of the potential ecological effects," he said. "If a disease or genetic defect arises in human beings, we'll be pretty quick to develop a treatment and get rid of it. But if it arises in animals and they breed in the wild, zoonotic and genetic diseases could take hold and wreak havoc on a population."

Choosing to generate sperm based on particular traits also raises the specter of eugenics—selective breeding to create a perfect race. "The Nazis killed offspring they considered defective based on a policy called "life not worth living," said Lynn. "In a way, screening sperm can be seen as a clean way to manipulate our genetic heritage."

If used in largescale livestock production, the potential lack of genetic variation could increase susceptibility to genetic and infectious diseases and ultimately put food security at risk, said Lynn.

"There are a lot of potential caveats and questions to be answered—if we do get sperm, what do we do with them—and safety concerns: Do we get normal offspring, what is the potential for cross-species disease transference. But from a practical point of view, the technique is not technically difficult, and the benefits are great," said Dobrinski.

"But any talk about using the technique in humans is highly speculative. Scientists hate to talk about something they haven't done, and there's been no work done on primates."

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