Freeze-dried mice: how a new technique could help conserve species

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Japanese scientists have succeeded in producing cloned mice using freeze-dried cells in a technique they believe could one day help conserve species and overcome the challenges of current biobanking methods.

The UN has warned that extinctions are accelerating in the world and at least one million species could become extinct due to human-induced impacts like climate change.

Facilities have sprung up around the world to preserve samples of endangered species in an effort to prevent their extinction through future cloning.

These samples are typically cryopreserved using liquid nitrogen or stored at extremely low temperatures, which can be costly and vulnerable to power outages.

They also usually involve sperm and eggs, which can be difficult or impossible to harvest 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 produce clones.

They experimented with two types of mouse cells and found that although freeze-drying killed them and caused significant DNA damage, they could still produce cloned blastocysts – a ball of cells that develop into an embryo.

From these, the scientists extracted stem cell lines which they used to create 75 cloned mice.

One of the mice survived a year and nine months, and the team also managed to mate female and male cloned mice with natural partners and produced normal pups.

The cloned mice produced fewer offspring than would be 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 at Yamanashi University’s School of Life and Environmental Sciences, who helped lead the study published in the journal Nature. Communications this month.

“We believe that in the future we can reduce abnormalities and increase the birth rate by researching freeze-drying protective agents and improving drying methods,” he told AFP.

“We have made a breakthrough in this area”

There are other disadvantages – the success rate of cloning mice from cells stored in liquid nitrogen or ultra-low temperatures is between 2 and 5%, while the freeze-dried method is only by 0.02%.

But Wakayama says the technique is still in its infancy, comparing it to the study that produced “Dolly”, the famous sheep clone – only one success after more than 200 trials.

“We think the most important thing is that cloned mice have been produced from freeze-dried somatic cells and we’ve achieved a breakthrough in this,” he said.

While the method is unlikely to entirely replace cryopreservation, it represents a “very exciting advance for scientists interested in biobanking threatened global biodiversity,” said Simon Clulow, senior research fellow at the Center for Ecology and Conservation. Conservation Genomics from the University of Canberra.

“It can be difficult and expensive to develop cryopreservation protocols and so alternatives, especially 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 already shown that freeze-dried mouse sperm can survive for at least a year at room temperature and believe somatic cells would too.

The technique could eventually “allow genetic resources around the world to be stored cheaply and securely,” Wakayama said.

This work is an extension of years of research into cloning and freeze-drying techniques by Wakayama and his partners.

One of their 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 and produced healthy baby mice.

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