The strange goal of researchers wanting to resurrect an extinct species of rats

Ever since the film

, the idea of ​​bringing extinct species back to life has fascinated people.

But where should scientists turn first?

Instead of focusing on iconic species like the woolly mammoth or the Tasmanian tiger, a team specializing in paleogenetics sought to determine the method that would bring the humble Rattus macleari back to life.

This species of rat endemic to Christmas Island in the Indian Ocean disappeared about 120 years ago.

The researchers didn't go so far as to actually recreate a living specimen, but say their study, published Wednesday in the journal

, shows how close scientists working on so-called "de-extinction" projects could come.

"I don't do de-extinction, but I think it's an interesting idea, and technically, it's very exciting," lead author Tom Gilbert of the Institute told AFP. University of Copenhagen.

Three possible techniques

Three techniques are explored to resuscitate extinct animals: crossing close species in order to find certain lost traits, cloning and finally genome editing.

It is on the latter that Tom Gilbert and his colleagues looked.

The idea is to take DNA from the extinct species, and compare its genome to similar modern species.

Once the nearest one has been selected, the CRISPR tool, dubbed molecular scissors, is used to edit the modern genome where it differs from the ancient one.

The cells thus modified could then be used to create an embryo, to be implanted in a surrogate mother.

The hypothesis is that black rats reported on board European ships decimated the local rat population.

The latter were tall, with a long yellow tail, and small round ears, according to a description in a scientific journal dating from 1887.

A loss of key functions

The researchers used Norway rats, commonly found in laboratories, as a modern reference species.

They determined that they could reconstruct 95% of the genome of the Christmas Island rat.

Although this proportion may sound like a great success, the 5% lost are part of regions of the genome controlling the sense of smell and the immune system: the resuscitated rat would thus certainly resemble the old one, but it would lack certain key functions.

The two species began to diverge 2.6 million years ago, evolutionarily not very long ago, but still too long ago to reconstruct the entire genome.

These results have important implications for ongoing “de-extinction” projects, such as that of an American company to revive a mammoth.

Mammoths, extinct around 4,000 years ago, are as distant from modern elephants as Rattus macleari is from brown rats.

Focus on protection

In Australia, a team is trying to revive the Tasmanian tiger, the last specimen of which died in captivity in 1936. But even if the gene editing technique was further improved, without being able to recompose a identical genome, the animals created would always present important differences.

If the goal is to bring [a species] back to its exact form, for example to reintroduce it into the wild, “that will never happen”, believes Tom Gilbert.

Moreover, the researcher admits that even if this science is fascinating, these projects of “de-extinction” provoke in him mixed feelings.

“I'm not convinced it's the best job you can do for your money,” he says.

“If you had to choose between resurrecting something and protecting something that still exists, I would bet on protection.

»

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