Mice stored at −20 °C for 16 years have been cloned, purportedly raising the possibility that extinct animals could be 'resurrected' from frozen tissue samples.
Researchers had previously cloned mice from frozen cells stored in chemicals that protect against the damaging effects of freezing. In the new study, Teruhiko Wakayama at RIKEN in Kobe, Japan, and his colleagues generated embryonic stem cells using nuclei harvested from mice that were frozen whole and without protective chemicals. They then transferred nuclei from the stem cells into unfertilized eggs that had had their nuclei removed. Surrogate mothers implanted with these eggs went on to produce several healthy offspring.
The finding paves the way for cloning extinct species such as the woolly mammoth, the authors claim.