Breakthrough could help conservationists revive dwindling populations of endangered species

Dorami, the black mouse on the left, is the first cloned mouse from freeze-dried skin cells and her offspring The white mouse is a normal male mouse for mating, and the small brown mice are Dorami's mouse pups. Photograph: University of Yamanashi

Researchers have created cloned mice from freeze dried skin cells in a world first that aims to help conservationists revive populations of endangered species.

The breakthrough paves the way for countries to store skin cells from animals as an insurance policy, as the cells can be used to create clones that boost the species’ genetic diversity if they become threatened with extinction in the future.

Many dwindling species suffer from inbreeding that drives up the risk of birth defects, but the loss of genetic diversity can also make animals more vulnerable to other threats, such as diseases, 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 risky: if there are power outages or the liquid nitrogen is not regularly topped up, the cells melt and become unusable. 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 allows genetic resources from around the world to be stored cheaply and safely,” said Prof Teruhiko Wakayama who led the work at the University of Yamanashi 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, researchers froze dried skin cells from mouse tails and stored them for up to nine months before trying to create clones from them. The 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 stocks of stem cells that were put through another round of cloning. The stem cells were inserted into mouse eggs emptied of their own nuclei, leading to embryos that surrogate mice carried to term. The first cloned mouse, named Dorami after a melon bread-loving robot in the Doraemon Manga series, was followed by 74 more. To check whether the clones had healthy fertility, nine females and three males were bred with normal mice. All the females went on to have litters.

Despite the achievement, the process is inefficient – freeze drying damaged DNA in the 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, leading to female mice being born from cells obtained from male animals. “If the same treatment could be performed in endangered species where only males survived, it would be possible to produce females and naturally preserve the species, the authors write in Nature Communications.

The work comes as scientists prepare to nurture offspring from the world’s first cloned black footed ferret, Elizabeth Ann, in an attempt 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 being able to store genetic material is “extraordinarily important” to maintain samples of species and also their genetic variation. But she said it was “paramount” to show the freeze-dried cells could be stored indefinitely if they are to provide an effective long-term solution.