The experts have taken another step forward in resurrecting the woolly rhinoceros by successfully reconstructing chromosomes collected from ancient skins in 3D for the first time.
About 52,000 years ago, a woolly rhinoceros was cryopreserved shortly after its death due to weather conditions, and its DNA was preserved in a glass-like state.
The exceptionally well-preserved specimen was excavated in northeastern Siberia in 2018, allowing an international team of scientists to analyze its skin tissue.
Now, they have succeeded in assembling a detailed reconstruction of the extinct species' chromosomes – thread-like structures made of DNA.
This is the first time scientists have been able to do this from such an ancient sample.
They say this could boost efforts to resurrect the woolly rhino by comparing the DNA with that of modern elephants.
Currently, a company called Colossal Biosciences is leading the effort to resurrect the woolly rhinoceros.
Their strategy was to take the genome of an Asian elephant and make a lot of small edits to its DNA.
The Asian elephant will then carry this offspring until it gives birth, giving birth to an elephant with many of the adaptations that allow the woolly rhinoceros to thrive in cold environments.
The team behind the new discovery says the genetic information preserved in this fossil is much more detailed than most ancient DNA fragments that have been discovered.
Not only were they able to see the genes present in the fossils, but they also got a rough idea of which genes were active and which were "off" – something they had never seen before.
Erez Lieberman Aiden, one of the study authors from Baylor College of Medicine in Texas, said it would help in the effort to resurrect the woolly rhino because it would help scientists understand which genes and sequences need to be "edited" in the elephant's genome to transform it into something similar to an extinct species.
"Like DNA, the entire chromosome is considered a fragile object that cannot survive outside the organism for a long time," he said. But under the right circumstances, chromosomes can actually survive for a long time. ”
"This surprise makes many things possible, like assembling an extinct genome, or seeing which genes are on and which are off in woolly rhino tissue, or checking the DNA loops that turn genes on and off."
"The overall plan for the resurrection is to use what we have learned about the woolly rhinoceros from DNA sequencing to engineer a species of elephant that is similar to the woolly rhinoceros in important ways."
Although versions of such plans have been around for some time, one "potential obstacle" is the lack of adequate understanding of the woolly rhinoceros genome – for example, how many pairs of chromosomes it has.
"The good news for the resurrection of the woolly rhino is that we don't have to worry about the whole set of potential obstacles because the overall structure of the genomes of the two species is very similar," Dr Aiden said. ”
"So localized DNA editing may indeed take us very far."
Their findings, he said, also helped pinpoint the specific edits needed to transform the Asian elephant into a woolly rhino.
"For example, we can now see the skin of the woolly rhinoceros and use these fossil chromosomes to see for the first time genes that are active in the skin of the woolly rhino that are not active in elephants and vice versa." He added.
"So now we can take a deeper look at which genes and sequences need to be focused on to make elephants look like woolly rhinos, and which sequences may be less important for this trait."
Although the method used in this study relies on exceptionally well-preserved fossils, the researchers are optimistic that it could be used to study other ancient DNA specimens, such as Egypt mummies.
Other authors of the study include researchers from the University of Copenhagen, the National Centre for Genome Analysis and the Centre for Genome Regulation in Spain.
The findings were published in the journal Cell.