Scientists dreams of resuscitation of mammoth

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.

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.

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 some day 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.

Bringing back extinct species is an interesting suggestion, Dr. Douglas E. Chandler of the Arizona State University School of Life Sciences commented.

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 long time worker in this field and is highly respected. He and his colleagues clearly are experts appropriate for this work."

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