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Sperm from ordinary frozen mice yield offspring

Posted on: Monday, 14 August 2006, 17:07 CDT

By Tan Ee Lyn

HONG KONG (Reuters) - Sperm extracted from mice and testes that have been frozen for as long as 15 years have yielded normal, healthy offspring in a study which researchers say heralds fresh hopes for bringing back extinct species.

Frozen sperm is now preserved with cryoprotectants, substances that protect it from freezing damage. However, defrosted sperm is not always capable of fertilising an egg.

But researchers from Japan, Britain and Hawaii have found that sperm can be frozen safely for much longer than previously thought, so long as they are kept in organs or whole carcasses and cooled slowly to minus-20 degrees Celsius or lower.

Using sperm from whole mice and testes that had been frozen for between one week and 15 years, they were able to fertilize eggs via microinsemination and obtain healthy offspring.

"Many people thought that sperm integrity could be retained for several months at most ... but the sperm nucleus is stronger than we expected," Atsuo Ogura of the Japanese government-funded Riken Bioresource Center told Reuters by telephone.

"It (sperm nucleus) is good for at least 15 years," he said, adding that offspring of the mouse that had been frozen for 15 years did not appear any different from the others.

GOOD NEWS: ANYONE CAN DO IT

The scientists used very simple freezing methods. The mouse that was frozen whole for 15 years was merely kept in a conventional freezer at minus-20 degrees C, Ogura said.

"This cryopreservation (freezing) technique is probably the simplest and anyone can do it. Liquid nitrogen is not necessary. Any conventional freezer or dry ice will work very well."

He said this method of freezing would work for many other mammals because mammalian sperm has a special DNA that "retains nucleic activity and keeps the nucleus alive."

"We can apply this method to many other mammals, it is very simple. Just put the testes or dead body into a freezer."

But he cautioned that carcasses must be allowed to cool slowly, or about two to three hours to reach minus-20 degrees C. Sperm frozen at lower temperatures would be better preserved.

"Degradation is minimal in liquid nitrogen (minus-196 degrees C). Molecules in the cells stay still in this condition, so the degradation will be minimal," he said.

The experiment, to be published online this week in the Proceedings of the National Academy of Sciences (http://www.pnas.org), may begin to change a long-standing reluctance to use frozen sperm in in vitro fertilization.

"This experiment proves that immotile sperm (which does not move) is just as good if frozen in good condition," Ogura said.

Looking ahead, Ogura said this breakthrough gives fresh hopes that extinct species may roam the earth again.

"Restoration of extinct species could be possible if male individuals are found in permafrost" he said, through injecting the sperm into eggs from females of closely related species.

Source: REUTERS

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