Toward Unlimited Cloning: Japanese Scientists Make 25 Generations of Mouse Clones

Using the same technique that was used to create Dolly the sheep, researchers from the RIKEN Center for Developmental Biology in Kobe, Japan, have identified a way to produce healthy mouse clones that live a normal lifespan and can be sequentially cloned indefinitely. Their study was published as the cover story of the March 7, 2013 issue of Cell Stem Cell. In an experiment that started in 2005, the team led by Dr. Teruhiko Wakayama has used a technique called somatic cell nuclear transfer (SCNT) to produce 581 clones of one original “donor” mouse, through 25 consecutive rounds of cloning. SCNT is a widely used cloning technique whereby a cell nucleus containing the genetic information of the individual to be cloned is inserted into a living egg that has had its own nucleus removed. It has been used successfully in laboratory animals, as well as farm animals. However, until now, scientists had not been able to overcome the limitations of SCNT that resulted in a low success rates and restricted the number of times mammals could be recloned. Attempts at recloning cats, pigs, and mice more than two to six times had failed. “One possible explanation for this limit on the number of recloning attempts is an accumulation of genetic or epigenetic abnormalities over successive generations,” explains Dr. Wakayama. To prevent possible epigenetic changes, or modifications to DNA function that do not involve a change in the DNA itself, Dr. Wakayama and his team added trichostatin, a histone deacetylase inhibitor, to the cell culture medium. Using this technique, they increased cloning efficiency by up to 6-fold. By improving each step of the SCNT procedure, the scientists were able to clone the mice repeatedly 25 times without seeing a reduction in the success rate.
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