Frozen sperm could be used to revive extinct species

Published 9:00 pm Monday, August 14, 2006

WASHINGTON – Descendants of extinct mammals such as the giant woolly mammoth might one day walk the Earth again.

It isn’t exactly Jurassic Park, but Japanese researchers are looking at the possibility of using sperm from frozen animals to inseminate living relatives.

So far they’ve succeeded with mice – some frozen as long as 15 years – and lead researcher Dr. Atsuo Ogura says he would like to try experiments in larger animals.

“In this study, the rates of success with sperm from 15 year-frozen bodies were much higher than we expected. So the likelihood of mammoths revival would be higher than we expected before,” Ogura said in via e-mail.

While frozen sperm is commonly used by sperm banks, the team led by Ogura, at Riken Bioresource Center in Ibaraki, Japan, worked with sperm from whole frozen mice and from frozen mouse organs.

“If spermatozoa of extinct mammalian species can be retrieved from animal bodies that were kept frozen for millions of years in permafrost, live animals might be restored by injecting them into (eggs) from females of closely related species,” the researchers said in a paper appearing in today’s issue of Proceedings of the National Academy of Sciences.

Intact mammoth bodies have been excavated from Siberian permafrost.

Elephants would be a potential candidate for insemination with frozen mammoth sperm, Ogura said. He also suggested experiments might be tried with extinct feline species and their modern relatives.

Dr. Robert McGaughey, laboratory director at the Institute for Reproductive Studies in Scottsdale, Ariz., said that since some of the whole frozen mice had been held for 15 years before obtaining the sperm nuclei “it clearly is possible that some day we may be able to obtain offspring from extinct animals frozen at reasonable temperatures for very long periods of time.”

Less enthusiastic was Dr. Peter Mazur, a biologist at the University of Tennessee who has worked with frozen eggs and sperm and is a past president of the Society for Cryobiology.

Mazur thinks the chance that frozen sperm from mammoths could be used to fertilize a related species is near zero.

“The storage temperature of frozen mammoths is not nearly low enough to prevent the chemical degradation of their DNA over hundreds of thousands of years,” he said.