Japanese Scientists Reach 58 Generations in Mouse Cloning Before Mutations Halt Experiment

Japanese scientists have reached a genetic breaking point in a two-decade experiment on mammal cloning, producing 58 generations of mice before accumulated mutations proved fatal to the final batch. The research, conducted at institutions including the University of Yamanashi, began in 2005 with a single female donor mouse and involved more than 30,000 cloning attempts, yielding over 1,200 cloned animals.

Researchers led by Teruhiko Wakayama and Sayaka Wakayama used somatic cell nuclear transfer, the technique that produced Dolly the sheep in 1996 and the first cloned mouse, Cumulina, in 1997. They transferred the nucleus from a donor cell into an enucleated egg, then implanted it into a surrogate mother. Each generation was cloned from a three-month-old female of the previous one, generating three to four new sets annually. For the first 25 generations, the process showed steady improvement, with success rates reaching over 15 percent and no visible health issues. An interim analysis in 2013 confirmed the mice were healthy, lived normal lifespans and produced viable offspring when mated naturally.

However, genomic sequencing of 10 mice from various generations revealed a...