Cloning Across Multiple Generations
March 8, 2013

Researchers Find Success In Multiple Generations Of Mouse Clones

Alan McStravick for - Your Universe Online

Known for such American gems as Caddyshack and Groundhog Day, Harold Ramis directed the cult classic Multiplicity starring Michael Keaton and Andie MacDowell in 1996. And in what had to have been a bit of marketing kismet, the film was released only 12 days after Dolly the sheep, the first mammal cloned from an adult somatic cell, was introduced to the world.

In the film, Doug Kinney, portrayed by Michael Keaton, was given the opportunity to clone himself so that he might be able to spend more time with his family. Through a series of misadventures, Multiplicity was able to accurately portray the pitfalls of excessive cloning, eventually yielding a dull, child-like clone of the main character.

A new study, however, conducted by researchers from the RIKEN Center for Developmental Biology in Kobe, Japan, utilized the same technique that created Dolly the sheep. The research team was able to produce healthy mouse clones able to live a normal lifespan. Unlike previous cloning endeavors, however, these mice can be sequentially cloned indefinitely.

Begun in 2005, the team´s experiment is led by Dr. Teruhiko Wakayama. The technique used for their cloning effort is known as somatic cell nuclear transfer (SNCT). Through this process, the team was able to produce 581 clones from one original ℠donor´ mouse. To date, they have repeated the technique through 25 consecutive rounds.

The technique of SNCT occurs when 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. Researchers in multiple disciplines have enjoyed moderate success with this technique previously.

One of the more difficult limitations of the process of SNCT yielded a diminished success rate coupled with a restriction on the number of times a mammal could be recloned. Previously, attempts at recloning cats, pigs and mice more than two to six times had resulted in catastrophic failure.

"One possible explanation for this limit on the number of recloning attempts is an accumulation of genetic or epigenetic abnormalities over successive generations" explains Wakayama.

Wakayama and colleagues worked to prevent these possible epigenetic changes by adding trichostati to the cell culture medium. Epigenetic changes are modifications to DNA function that do not involve a change to the DNA itself. The addition of trichostatin, a histone deacetylase inhibitor, increased the efficiency of their cloning efforts by up to 6-fold.

Between 2005 and today, the team has been able to clone the mice repeatedly 25 times without seeing any diminishment in the success rate. Each of the 581 mice obtained via this technique were all fertile, allowing them to give birth to healthy pups. Additionally, the cloned mice were able to live the normal lifespan of a mouse which is approximately two years.

"Our results show that there were no accumulations of epigenetic or genetic abnormalities in the mice, even after repeated cloning," conclude the authors.

Wakayama adds, "This technique could be very useful for the large-scale production of superior-quality animals, for farming or conservation purposes."

Just three years after the inception of their study, Wakayama and his team made headlines when they were able to create viable clones, utilizing the SNCT technique, from the bodies of mice that had been frozen for 16 years.

The study is published this week in the journal Cell Stem Cell.