The possum, or Tasmanian tiger, became extinct in 1936
huge life science
The genome of the extinct possum has been almost completely sequenced, the company that brought it back from extinction, Colossal, has announced. The group says the genome is more than 99.9 percent complete and that just 45 gaps will soon be filled, but it has not provided any evidence to support that claim.
“It’s quite difficult to obtain the complete genome of almost any organism,” says Emilio Marmol Sánchez of the University of Copenhagen, Denmark, whose team first extracted RNA from preserved quolls. For example, the last few holdouts of the human genome have only been fully sequenced in the past few years.
Quosos, also known as Tasmanian tigers, were once carnivorous marsupials found throughout Australia, but by the time European explorers arrived they were restricted to Tasmania. The last known possum died in a zoo in 1936.
The preserved possum genome was first sequenced in 2017 using tissue from a then 108-year-old possum pouch preserved in alcohol. However, this genome was far from complete and had many gaps. Colossal, which is also currently aiming to recreate the woolly mammoth, says it has nearly completed the genome with the help of additional DNA from a 120-year-old tooth.
“While our genome is not as complete as the most complete human genome, we were able to take advantage of some of the same technologies,” said Andrew of the University of Melbourne in Australia, a member of Colossal’s scientific advisory board. Pask said.
Completely deciphering the genomes of plants and animals is difficult because they contain large sections of the same sequence that repeat over and over again. Standard techniques for sequencing small segments of DNA at a time do not work for these parts. This is like trying to reconstruct a book from a list of words in the book.
New, long-read techniques can sequence much larger segments of DNA, equivalent to entire pages of a book. However, these methods are not very useful because old DNA is usually split into many small pieces.
“Most ancient samples preserve DNA fragments that are a few dozen or, if we’re lucky, a few hundred bases long,” Pask says. “The samples we had access to were so well preserved that we were able to recover DNA fragments several thousand bases long.”
There is no direct way to know how complete it is, given that there are no other possum genomes to compare it to. Instead, Pask says Colossal uses other closely related species in the same family to make this estimate.
But even if the genome were as complete as Colossal thinks and could indeed fill in the remaining gaps, there is currently no viable way to generate living cells containing this genome. Instead, Colossal plans to genetically modify a living marsupial called a fat-tailed dunnart to resemble a possum.
“This is rather a reproduction of some characteristics,” says Marmol Sánchez. “It would not be an extinct animal, but a very strange and modified version of a modern animal, similar to our image of an extinct animal.”
Colossal announces record 300 gene edits It affects the genome of Dunnart cells growing in culture. So far, the changes have been small, but Pask says the team plans to swap out tens of thousands of base pairs of thylacine DNA in the near future. He says it’s not yet clear how much editing will be needed to achieve the company’s goal of recreating the sugar glider.
When asked why Colossal did not provide any evidence to support its claims, the company’s CEO, Ben Lamb, said that the company’s sole focus was on eradicating extinction and that the scientific literature He said it was not writing. “We’re not an academic lab whose main focus is papers,” Lamb says. “We will continue to make progress much faster than the process of writing a scientific paper.”
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(Tag to translate) Genetic modification
