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Cloned Mice Obtained Using Frozen Tissue

Technique could be used to clone extinct species

WEDNESDAY, Nov. 5 (HealthDay News) -- Cloned mice have been obtained using mouse tissue frozen for up to 16 years, suggesting that it may be possible to clone extinct species where only frozen tissue is available, according to a report published online Nov. 3 in the Proceedings of the National Academy of Sciences.

Sayaka Wakayama, from RIKEN in Kobe, Japan, and colleagues examined whether cell nuclei from thawed mice that had been frozen without any cryoprotectants could be used to generate embryonic stem cell lines and cloned animals.

The researchers found that nuclei from brain tissue were most effective at producing cloned embryos when injected into enucleated oocytes, even nuclei taken from mice frozen at -20 degrees Celsius for up to 16 years. No cloned mice were obtained from cloned embryos produced from mice frozen 16 years. However, the cloned embryos were used to generate embryonic stem cell lines, which after a second round of nuclear transfer into oocytes were able to produce four cloned mice and nine chimeric clonal mice.

"Thus, nuclear transfer techniques could be used to 'resurrect' animals or maintain valuable genomic stocks from tissues frozen for prolonged periods without any cryopreservation," Wakayama and colleagues conclude.

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