12th March, 2013
Japanese biologists say they’ve created normal, healthy mouse clones with a new technique that can produce copies of copies, and so on, with no apparent limit.
The new method seems to sweep aside barriers to safe, efficient cloning, said the researchers. They used a variant of the technique that in 1996 led to the first mammal cloned from an adult cell, Dolly the sheep. The procedure, called somatic cell nuclear transfer, involves putting a cell nucleus containing the genetic information of the creature to be cloned, into a living egg with its own nucleus removed.
Scientists have previously struggled with low success rates and limits on how many times mammals could be recloned. Attempts at recloning cats, pigs and mice more than two to six times had failed.
In the new work, Teruhiko Wakayama at the RIKEN Center for Developmental Biology in Kobe, Japan, led a team that tweaked the technique to make 581 clones of one original mouse through 25 consecutive rounds of cloning. There was no visible drop in the success rate, the researchers said, reporting their findings March 7 in the journal Cell Stem Cell.
“One possible explanation for this [past] limit on the number of recloning attempts,” Wakayama said, “is an accumulation of genetic or ‘epigenetic’ abnormalities” over generations. Epigenetic changes are alterations to DNA function that don’t involve a change in the DNA code itself.
To prevent these aberrations, Wakayama and his team added a substance called trichostatin to the cell culture medium used for the process. Trichostatin is a histone deacetylase inhibitor, a compound that prevents chemical changes to DNA-associated structures called histones. These changes in turn can cause epigenetic abnormalities by affecting the way DNA is “packaged.”
Wakayama and colleagues said they increased cloning efficiency by up to sixfold and improved each step of the procedure. The 581 mice obtained through sequential cloning were all healthy, fertile, gave birth to healthy pups and lived about two years, like normal mice, the scientists said.
“Our results show that there were no accumulations of epigenetic or genetic abnormalities in the mice, even after repeated cloning,” wrote the authors. “This technique could be very useful for the large-scale production of superior-quality animals, for farming or conservation purposes,” added Wakayama, who also made the news in 2008 when his team created clones from the bodies of mice frozen for 16 years.
.Courtesy of the RIKEN Center for Developmental Biology and World Science staff