Scientists point the way to ‘resurrect’ extinct mouse 120 years ago

Ever since the movie “Jurassic Park,” the idea of ​​bringing extinct animals back to life has captured the public’s imagination, but where should scientists turn their attention first?

Instead of focusing on iconic species like the woolly mammoth or the Tasmanian tiger, a team of paleogeneticists studied how they could “revive”, using gene editing, the humble Christmas Island mouse, extinct for 120 years.

While they failed to create a living species, they say their research, published Wednesday in Current Biology, demonstrates how close scientists working on extinction projects are to achieving the goal using current technology.

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

There are three ways to bring back extinct animals: back-breeding related species to gain lost traits; cloning, which was used to create Dolly the sheep in 1996; and finally gene editing, the method that Gilbert and his colleagues are studying.

The idea is to take the surviving DNA of an extinct species, compare it to the genome of a closely related modern species, and then use techniques like Clustered Regularly Interspaced Short Palindromic Repeats (CRISPR) to edit the modern genome where there are differences. .

The edited cells can then be used to create an embryo that implants into a surrogate host.

Gilbert explains that ancient DNA is like a book that has been put through a shredder, while the genome of the modern species is like a “summary book” that can be used to piece together the incomplete pieces.

His interest in the Christmas Island mouse was piqued when a colleague studied the animals’ skin for evidence of pathogens that caused their extinction around 1900.

Black rats brought by European ships are believed to have wiped out the native species, described in the Proceedings of the Zoological Society of London in 1887 as a “new rat”, larger, with a long yellow-tipped tail and rounded ears.

Missing key functions

The team of scientists used brown mice, commonly used in laboratory experiments, as the modern reference species, and found that they could reconstruct 95% of the Christmas Island mouse genome.

It might seem like a huge success, but the 5% that failed to recover belonged to regions of the genome that control smell and immunity, meaning this mouse could have looked like the originals, but without these key functions.

“What we’re left with is that even if we basically have the ancient DNA in perfect condition, with a very good sample and sequenced as much as possible, we’re still missing 5%,” explained Gilbert.

The two species diverged about 2.6 million years ago, close to the evolutionary era, but not far enough to completely reconstruct the genomes of the lost species.

The discovery has important implications for de-extinction efforts, such as the American bioscience company Colsa’s project, which seeks to resurrect the mammoth, which went extinct about 4,000 years ago.

Mammoths are roughly the same evolutionary distance from modern elephants as brown mice are from Christmas Island mice.

Meanwhile, teams in Australia are trying to revive the Tasmanian tiger, or thylacine, whose last specimen died in captivity in 1936.

Even if gene editing were perfected, animals replicated using this technique would have certain critical shortcomings.

“Let’s say you bring back a mammoth just to have a furry elephant in a zoo to make money or raise conservation awareness, it doesn’t really matter,” Gilbert warned.

But if the goal is to bring these animals back to their exact original form, “that will never happen,” he added.

Gilbert admitted that while science was fascinated by extinction projects, he had mixed feelings.

“If you had to choose between bringing something back or protecting it, I would put my money in protection.”