Study shows how gene editing can bring extinct rats back to life

Since the movie Jurassic Park, the idea of ​​bringing extinct animals back to life has caught the public’s imagination, but what could scientists turn their attention to first?

Instead of focusing on iconic species like the woolly mammoth or he Tasmanian tigera team of paleogenists has studied how, by editing genes, they could resurrect the humble rat of Christmas Island, which became extinct about 120 years ago.

Although they did not follow through and created a living specimen, they say their article, published Wednesday in Current Biology, demonstrates the extent to which scientists working on extinction projects could use current technology.

“I’m not doing the extinction, but I think it’s a very interesting idea, and it’s technically very exciting,” lead author Tom Gilbert, an evolutionary geneticist at the University of Copenhagen, told AFP.

There are three ways to recover extinct animals: the reproduction of species related to retreat to achieve lost traits; cloning, which was used to create Dolly the sheep in 1996; and finally genetic editing, which Gilbert and his colleagues looked at.

The idea is to take the surviving DNA of an extinct species and compare it to the genome of a closely related modern species, and then use techniques such as CRISPR to edit the genome of the modern species in places where it differs.

The edited cells could then be used to create an embryo implanted in a replacement host.

Gilbert said ancient DNA was like a book passed through a shredder, while the genome of a modern species is like an intact “reference book” that can be used to put together fragments of its degraded counterpart.

His interest in rats on Christmas Island was aroused when a colleague studied his skins for evidence of the pathogens that led to their extinction around 1900.

Black rats on European ships are thought to have wiped out native species, described in an 1887 entry in the London Zoological Society Act as a large, thin “new rat” with a long tail. yellow tip and small rounded. ears.

“We sequenced shit”

The team used brown rats, commonly used in laboratory experiments, as a modern reference species, and found that they could reconstruct 95 percent of the genome of the Christmas Island rat.

This may seem like a big hit, but the five percent that could not be recovered were from regions of the genome that controlled odor and immunity, meaning the recovered rat might look the same but would not have key functionality.

“What brings me home is that even if we have basically the perfect situation of old DNA, we have a very good sample, we’ve sequenced hell, we’re still five percent missing,” Gilbert said. .

The two species diverged about 2.6 million years ago: close in evolutionary time, but not close enough to completely reconstruct the entire genome of the lost species.

This has important implications for extinction efforts, such as a project by the American bioscience firm Colossal to resurrect the mammoth, which became extinct about 4,000 years ago.

Mammoths have about the same evolutionary distance as modern elephants as brown rats and Christmas Island rats.

Meanwhile, Australian teams are looking to revive the Tasmanian tiger, or thylacine, the last surviving member of which died in captivity in 1936.

Even if genetic editing were perfected, replicas created with the technique would therefore have certain critical shortcomings.

“Let’s say you bring a mammoth just to have a furry elephant in a zoo to raise money or raise awareness about conservation; it really doesn’t matter,” he said.

But if the goal is to get the animal back to its original original form, “this will never happen,” he said.

Gilbert admitted that while science was fascinating, he had conflicting feelings about extinction projects.

“I’m not convinced it’s the best use of anyone’s money,” he said. “If you had to choose between carrying something or protecting what was left, I would put my money under protection.”

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