Around 120 years ago, “hyperdisease conditions” on Australia’s Christmas Island brought by European ships spelled the demise of the island’s unique species of rat, but now, scientists are exploring the possibility of resurrecting this extinct creature.
While in popular culture the “de-extinction” of prehistoric animals such as dinosaurs and mammoths appeals to the imagination, the examination of resurrecting a more recently extinct creature provides new insights into the extent to which it is possible.
The team of palaeontologists investigating the limits of what is possible in bringing back the Christmas Island rat, Rattus macleari, said that “de-extinction work is defined by what is unknown”.
This is because the process depends on rebuilding degraded DNA, which therefore doesn’t contain all the genetic information required to rebuild the full genome of the animal.
This is the case with carcasses of mammoths found frozen in ice in Siberia – the freezing of the ice has usually damaged the DNA.
Christmas Island Rat
In the study, published in Current Biology, the focus was on a species of rat that became extinct a century ago and lived on Australia’s Christmas Island.
This rat is scientifically known as “Rattus macleari” and it disappeared 100 years ago due to an epidemic carried by European ships, and scientists confirm that they are not seeking to bring it back to life in order to fill the sewage channels in the cities with it, but they are seeking to find a way to revive the other extinct creatures, Which is a huge challenge because of the damage on the DNA available from them.
According to Tom Gilbert, a geneticist at the Danish University of Copenhagen and a participant in the research, “The difference between modern and ancient DNA is like a whole book and a torn one. Both contain information, but it is difficult to understand the information in the torn book.”
Is it an elusive miracle?
the Christmas Island rat has a close evolutionary descendent in the Norway rat. That larger rat, which can weigh more than a pound and be 16 inches long, is the species that dwells in our sewers and has become a common laboratory research subject.
Using gene-editing technology, researchers attempted to recreate the genome of the Christmas Island rat and found that the two rats shared about 95% of the same genetic material. But they also found that about 5% of its original genes could not be recovered, they reported Wednesday in Current Biology, the peer-reviewed scientific journal.
“They have evolved to be so different, we can’t recover the sequence,” said Tom Gilbert, one of the study’s co-authors and the head of the Center for Evolutionary Hologenomics at the University of Copenhagen in Denmark.
What it takes to resurrect a rat
The researchers at the University of Copenhagen and Shantou University in China used DNA from two dried Christmas Island rat skins to sequence its genome and compare it to the modern Norway rat. In comparing the two, the researchers found that some of the missing Christmas Island rat genes dealt with its ability to smell.
So a reborn Christmas Island rat might “lack attributes likely critical to surviving in its natural or natural-like environment,” they write in the report.
However, using CRISPR gene editing technology, the rat to be brought back could be a hybrid animal including the immunity genes of the Norway rat, which “could even have some potential benefit,” they wrote.
But first, Gilbert plans to try editing the genome of a black rat to change it into a Norway rat, he said in a description of the research on the university’s website. “It’s a fascinating idea in technology, but one has to wonder if that’s the best use of money as opposed to keeping the things alive that are still here,” he said.
Can mammoths be revived?
As part of these de-extinction attempts, the startup Colossal spent last year $15 million on research to bring the mammoth back to life, which became extinct 4,000 years ago. In the past two decades, it was believed that this creature that walks on frozen land reduces emissions from melting ice.
Tom Gilbert explains that the goal of this research is not to return the mammoth in its original form, but to return a species that can coexist with the rest of the other species, i.e. an elephant with mammoth characteristics.
Study paper: https://www.cell.com/current-biology/fulltext/S0960-9822(22)00249-4