Japanese scientists have successfully produced cloned mice using freeze-dried cells in a technique they believe could one day help conserve species and overcome challenges with current biobanking methods.
The United Nations has warned that extinctions are accelerating worldwide and at least a million species could disappear due to human-caused impacts such as climate change.
Facilities have sprung up around the world to preserve specimens of endangered species with the aim of preventing their extinction from future cloning.
These samples are generally cryopreserved using liquid nitrogen or stored at extremely low temperatures, which can be costly and prone to power outages.
They also usually contain sperm and ova, which are difficult or impossible to obtain from old or infertile animals.
Scientists at Japan’s Yamanashi University wanted to see if they could solve these problems by freeze-drying somatic cells — any cell that isn’t a sperm or egg — and trying to make clones.
They experimented with two types of mouse cells and found that although they were killed by freeze-drying and caused significant DNA damage, they could still produce cloned blastocysts — a ball of cells that develops into an embryo.
From these, the scientists extracted stem cell lines, from which they created 75 cloned mice.
One of the mice survived a year and nine months, and the team also successfully mated cloned female and male mice with naturally born partners and produced normal pups.
The cloned mice produced fewer offspring than would have been expected from naturally born mice, and one of the stem cell lines developed from male cells produced only female mouse clones.
“Improvement shouldn’t be difficult,” said Teruhiko Wakayama, a professor in the Faculty of Life and Environmental Sciences at Yamanashi University who helped lead the study, published this month in the journal Nature Communications.
“We believe that in the future we will be able to reduce anomalies and increase the birth rate by searching for freeze-drying preservatives and improving drying methods,” he told AFP.
– “Very exciting progress” –
There are other disadvantages: The success rate of cloning mice from cells stored in liquid nitrogen or at ultra-low temperatures is between two and five percent, while the freeze-dried method is only 0.02 percent.
But Wakayama says the technology is still in its early stages, comparing it to the study that produced “Dolly,” the famous cloned sheep — a single success after more than 200 attempts.
“We think the most important thing is that cloned mice have been made from freeze-dried somatic cells and that we have made a breakthrough in this area,” he said.
Although the method is not likely to completely replace cryopreservation, it represents a “very exciting advance for scientists interested in biobanking of threatened global biodiversity,” said Simon Clulow, senior research fellow at the University of California’s Center for Conservation Ecology and Genomics canberra
“Cryopreservation protocols can be difficult and expensive to work out, so alternatives, particularly those that are cheaper and more robust, are extremely welcome,” added Clulow, who was not involved in the research.
The study stored the freeze-dried cells at minus 30 degrees Celsius, but the team has previously shown that freeze-dried mouse sperm can survive at least a year at room temperature and believe somatic cells would do the same.
The technique could eventually “make it possible to cheaply and safely store genetic resources from around the world,” Wakayama said.
The work is a continuation of years of research into cloning and freeze-drying techniques by Wakayama and its partners.
One of their most recent projects involved freeze-drying mouse sperm sent to the International Space Station. Even after six years in space, the cells were successfully rehydrated on Earth, producing healthy mouse pups.
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