The discovery paves the way for countries to store animal skin cells as an insurance policy, as the cells can be used to create clones that boost the genetic diversity of species if they are threatened with extinction in the future. Many species in decline suffer from inbreeding that increases the risk of genetic defects, but the loss of genetic diversity can also make animals more vulnerable to other threats, such as disease, which exacerbate the pressures they face. While scientists have used frozen cells to produce clones for conservation projects, the cells are kept in liquid nitrogen which is expensive and dangerous: if there are power outages or the liquid nitrogen is not replenished regularly, the cells melt and become useless. Freeze-dried sperm can also be used to create clones, but cannot be obtained from all animals. “If these cells can be preserved without liquid nitrogen using freeze-drying technology, it enables cheap and safe storage of genetic resources from around the world,” said Professor Teruhiko Wakayama who led the work at Yamanashi University in Japan. “Developing countries will be able to store their own valuable genetic resources in their own countries. Also, even in endangered species where only males survive, this technology can be used to create females to revive the species.” In the latest work, the researchers freeze-dried skin cells from mouse tails and stored them for up to nine months before trying to clone them. Freeze-drying processes killed the cells, but the scientists found they could still create early-stage cloned embryos by inserting the dead cells into mouse eggs that had their own nuclei removed. These early-stage mouse embryos, known as blastocysts, were used to create stem cell stocks that underwent another round of cloning. The stem cells were inserted into mouse eggs that had been emptied of their own nuclei, leading to embryos that the surrogate mice eventually carried. The first cloned mouse, named Dorami after a melon-loving robot in the Doraemon Manga series, was followed by 74 more. To test whether the clones had healthy fertility, nine female and three male mice were bred with normal mice. All females continued to have litters. Subscribe to First Edition, our free daily newsletter – every morning at 7am. BST Despite the achievement, the procedure is inefficient – freeze-drying damaged DNA in skin cells – and the success rate for creating healthy female and male mouse pups was only 0.2 to 5.4%. In some of the cells, the Y chromosome was lost, resulting in female mice being born from cells taken from male animals. “If the same treatment could be carried out in endangered species where only males survived, it would be possible to produce females and of course preserve the species,” the authors write in Nature Communications. The work comes as scientists prepare to breed offspring from the world’s first cloned black-footed ferret, Elizabeth Ann, in a bid to boost the species’ genetic diversity. The animal was cloned from cells deep-frozen in liquid nitrogen 35 years ago. Dr Alena Pance at the University of Hertfordshire said the ability to store genetic material is “extremely important” for preserving species samples and also their genetic diversity. However, he said it was “of the utmost importance” to show that the freeze-dried cells could be stored indefinitely if they were to provide an effective long-term solution.
