Long-Frozen Mice "Resurrected" in Cloning Experiment

The new approach, once thought impossible, may lead to new experiments that give birth to woolly mammoths or other species that are extinct.

Dr. Teruhiko Wakayama, from the RIKEN Center for Developmental Biology (Kobe; Japan), and coworkers collected nuclei from the brain cells of frozen mice and injected them into empty oocytes that had all DNA removed from them. Those were then used to create cloned embryos, which were used to harvest stem cells for a second cycle of cloning.

"We have demonstrated that healthy cloned mice and chimeric clonal mice could be obtained by nuclear transfer using donor nuclei from cells obtained from bodies frozen without cryoprotectants for up to 16 years,” reported the team of researchers.

Moreover, the researchers noted, other sources of frozen nuclei could help in efforts to revive extinct species. This would increase the chances of finding tissues in good condition. Currently, the lack of suitable species for recipient oocytes and for surrogate mothers is one of the major problems that needs to be solved for the technique to be applied in extinct or endangered animals.

"Thus, nuclear transfer techniques could be used to ‘resurrect' animals or maintain valuable genomic stocks from tissues frozen for prolonged periods without any cryopreservation,” they wrote in their article, which was published in the November 14, 2008, issue of the journal Proceedings of the [U.S.] National Academy of Sciences (PNAS).

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RIKEN Center for Developmental Biology