BIG STEPS
Hope for woolly mammoth ‘de-extinction’ after DNA from frozen 52,000-year-old remains found – including ‘giant foot’
The "freeze-dried" fossil could hold the key to reviving the enormous creature through genetic engineering
SCIENTISTS have sequenced a woolly mammoth's genome and chromosomal structures for the first time in history.
The feat, published today in Cell, is also the first of its kind for any ancient DNA sample.
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And it might hold the key to bringing the collossal creature back from the dead.
The research was made possible by a perfect storm of conditions that preserved the mammoth's DNA in a glass-like state.
An international research team took chromosomes from 52,000-year-old remains uncovered in northeastern Siberia six years ago.
The mammoth had been "freeze-dried" shortly after death and was eerily well-preserved, making it an ideal specimen.
Scientists soon discovered the fossilized chromosomes were a million times longer than most ancient DNA fragments.
They were able to assemble a complete set of chromosomes, known as a karyotype.
This provided evidence of how the mammoth’s genome was organized within its cells and which genes were active in the tissue from which the DNA was extracted.
“This is a new type of fossil, and its scale dwarfs that of individual ancient DNA fragments,” said corresponding author Erez Lieberman Aiden.
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“It is also the first time a karyotype of any sort has been determined for an ancient sample.”
Researchers tested dozens of samples over a five-year span before landing on the "freeze-dried" woolly mammoth.
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“The nuclear architecture in a dehydrated sample can survive for an incredibly long period of time," corresponding author Olga Dudchenko explained.
To reconstruct the mammoth’s genome, the researchers took DNA from a skin behind the creature's ear.
They used a method called Hi-C that allows them to detect which sections of DNA are likely to be in close spatial proximity and interact with each other in their natural state in the nucleus.
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Corresponding author Marc A. Marti-Renom likened the process to building a puzzle without having a picture of the final result to work from.
“Hi-C allows you to have an approximation of that picture before you start putting the puzzle pieces together," he explained.
Basing their work on human genome mapping, the team combined the results of the Hi-C analysis with DNA sequencing to identify the interacting DNA sections and create a map.
It was revealed that woolly mammoths had 28 chromosomes, the same number as modern Asian and African elephants.
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The remarkable fossil retained significant detail, including the physical structures that allow genes to be controlled.
This allowed the researchers to identify once active and inactive genes within the mammoth’s skin cells.
Compared to its closest surviving relative, the Asian elephant, the mammoth cells had distinct patterns of gene activation possibly related to its woolly hair and cold tolerance.
“For the first time, we have a woolly mammoth tissue for which we know roughly which genes were switched on and which genes were off,” Marti-Renom said.
“This is an extraordinary new type of data, and it’s the first measure of cell-specific gene activity of the genes in any ancient DNA sample.”
Woolly mammoth – the key facts
Here's what you need to know...
- The woolly mammoth is an ancient creature that is now extinct
- The species first appeared 400,000 years ago in East Asia when it “diverged” from the steppe mammoth
- Its closest living relative today is the Asian elephant
- Woolly mammoths are one of the best-studied prehistoric animal, due to the discovery of frozen carcasses in Siberia and Alaska
- We also have evidence of them in the form of skeletons, teeth, droppings and cave paintings
- A woolly mammoth was similarly sized to a modern African elephant
- Males were typically around 11ft tall, and weighted up to 6 metric tons
- Females were smaller at 9.5ft tall and 4 metric tons
- A newborn calf weighed around 90 kilos, or 200 lb
- Woolly mammoths were well-adapted to the frosty temperatures of the last Ice Age, thanks to their fur coats
- They largely disappeared from the mailand around 10,000 years ago, thanks to a shrinking habitat and hunting by humans
- Isolated populations survived on Arctic islands until as recently as 4,000 years ago
The team hopes the methods used in the study could be replicated to examine other ancient DNA specimens.
However, they note that its success depends on well-preserved fossils, which are few and far between.
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The results also bring scientists one step closer to de-extinction, as the karyotype provides a potential template for genetic engineering.
Geneticists led by Harvard Medical School’s George Church are among those leading the charge.
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