Frozen Sperm Revive Jurassic Park Dreams

Aug. 14, 2006 — Virtually all male animals — including people and extinct species — can reproduce after death if bodies or sexual organs are kept frozen, suggests a new study.

The study's goal, say the researchers who conducted it, is to bring extinct species back to life.

They think it might be possible, for example, to revive woolly mammoths or at least produce a mammoth hybrid. A 23,000-year-old Siberian mammoth was found preserved in permafrost in 1999.

The technique could also help scientists prevent new animal extinctions, which have been on the rise in recent decades.

Preserving sperm is remarkably simple, as Atsuo Ogura, who worked on the study, explained to Discovery News.

"Sperm can be kept frozen safely...for longer than we expected, as long as the organs or dead bodies are cooled slowly to -20 degrees Celsius (-4 degrees F) or lower," he said.

Cryopreservation is probably the simplest way to do that, said Ogura. "Anyone can do it. Liquid nitrogen is not necessary. Any conventional freezers or dry ice will work very well," he said.

Scientists commonly freeze sperm for medical purposes, but defrosted sperm does not always successfully fertilize eggs.

Instead of working with sperm by itself, Ogura and his team instead studied sperm housed in the tubular structures within testes, the whole testes themselves, and even entire male mouse bodies — some of which had been in a freezer for 15 years. Suspension in a potassium-rich liquid seemed to best preserve them.

The researchers also tested whether frozen male sexual organs could be transported internationally via shipment on dry ice. In most cases, the extracted sperm produced normal offspring.

While live female mice were available to provide eggs, Ogura said eggs provided by a related species also might work — resulting in hybrid offspring.

Findings are published in this week's Proceedings of the National Academy of Sciences.

Jerry Yang, a scientist at the Connecticut Center for Regenerative Biology, told Discovery News that "this is an exciting report."

Yang added, "These findings are very important for saving endangered or special valuable animals."

J.M. Cummins, associate professor of anatomy at Murdoch University in Western Australia, echoed Yang's remarks.

"This is certainly an extraordinary finding and pushes the limit on what we can expect from cryostorage of reproductive material. The old idea that sperm have to be biologically 'alive' to transmit the genome clearly has to be re-thought," said Cummins.

He added, "The Jurassic Park idea was thought to be pure science fiction by sperm biologists; now we are not so sure."

Given the findings, Ogura advises conservationists and zoo personnel to collect testes from dead male animals as soon after death as possible, and to store them in ordinary freezers.