WASHINGTON — Descendants of extinct mammals like 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 an interview 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 Tuesday's issue of Proceedings of the National Academy of Sciences.
Intact mammoth bodies have been excavated from Siberian permafrost.
Could it happen?
Dr. Robert W. McGaughey, laboratory director at the Institute for Reproductive Studies in Scottsdale, Ariz., commented that since some of the whole frozen mice had been held for 15 years before obtaining the sperm nuclei "it clearly is possible that someday we may be able to obtain offspring from extinct animals frozen at reasonable temperatures for very long periods of time."
The downside, added McGaughey, who was not part of the research team, is that an extinct animal probably would have to have been continuously maintained at a low temperature to avoid thawing/refreezing damage.
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.
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 commented. And "even if the temperature were low enough to prevent chemical degradation, that would not prevent serious damage over those time periods from background radiation, which includes cosmic rays."
What about the egg?
Bringing back extinct species is an interesting suggestion, Dr. Douglas E. Chandler of the Arizona State University School of Life Sciences commented.
"The trick, however, is to find an acceptable species that would act as the mother," added Chandler, who was not part of Ogura's research team. If an elephant egg were used "the offspring would not be a mammoth but a hybrid between an elephant and a mammoth. If one wanted a true mammoth one would have to find a source of viable mammoth (eggs) to fertilize and implant and this is a much dicier proposition."
McGaughey agreed, "It is unlikely eggs from such frozen animals would survive; therefore only the sperm would be available to put into eggs from an existing and appropriate modern mammal to approximate the extinct one."
The research requires considerable technical expertise, Chandler said, adding that Ryuzo Yanagimachi, one of Ogura's researchers, "is a longtime worker in this field and is highly respected. He and his colleagues clearly are experts appropriate for this work."
Ogura's research was funded by the Japanese ministries of education and health, and the Human Science Foundation of Japan.
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