Three photos of the dried remains of a Tasmanian tiger from the collection at the Swedish Museum of Natural History in Stockholm, used for the scientific study
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The Tasmanian tiger is a carnivorous marsupial with the size of a dog and the appetite of a wolf that once roamed the Australian continent and neighboring islands. Because of humans, the species is now extinct.
But that doesn’t mean scientists have stopped studying it. Researchers reported this week that they recovered RNA from dried skin and muscle of a Tasmanian tiger stored since 1891 in a museum in Stockholm.
RNA is a genetic material present in all living cells that has structural similarities to DNA. In recent years, scientists have been able to extract DNA from ancient animals and plants, some of them more than 2 million years old. But for the first time they succeeded with RNA – significantly more unstable than DNA, from an extinct species.
The ability to extract, sequence and analyze ancient RNA could spur other scientists’ efforts to recreate extinct species. Recovering RNA from old viruses can also help decipher the cause of past pandemics.
DNA vs. RNA
DNA (deoxyribonucleic acid) and RNA (ribonucleic acid), biomolecular cousins, are fundamental molecules in cell biology.
DNA is a double-stranded molecule that contains the genetic code of an organism, carrying the genes that give rise to all living things. RNA is a single-stranded molecule that carries genetic information obtained from DNA, putting that information into practice. RNA synthesizes an array of proteins that an organism needs to live and works to regulate cellular metabolism.
“RNA sequencing provides insight into the true biology and regulation of metabolism that occurred in the cells and tissues of Tasmanian tigers before they went extinct,” says geneticist and bioinformatician Emilio Marmol Sánchez of the Center for Paleogenetics and SciLifeLab in Sweden.
He is the lead author of the study published in the journal Genome Research.
“If we want to understand extinct species, we need to understand what gene complements they have, what their genes did and which ones were active,” adds Mark Friedländer of Stockholm University and SciLifeLab, who co-authored the study.
There were questions about how long the RNA could survive under the conditions (room temperature in a cabinet) where these remains were stored. The remains in the Swedish Natural History Museum were in a state of semi-mummification, with preserved skin, muscles and bones, but lost internal organs.
“Most researchers think that RNA would survive for a very short time – days or weeks, at room temperature. This is probably true when the samples are wet or moist. In our case, they were dried, and that changes things,” explains the evolutionary geneticist Lyubov Dalen from the Center for Paleogenetics.
Sacrifice of man
The first blow to its population is associated with the appearance of man in Australia – about 50 thousand years ago. The arrival of European colonizers in the 18th century proved fatal to the existence of the species after it was declared dangerous to livestock and a bounty was placed for its extermination. The last known Tasmanian tiger died in a zoo on the island of Tasmania in 1936.
The Tasmanian tiger resembles a wolf except for the tiger-like stripes on its back. It was a top predator, hunting kangaroos and other prey.
“The story of the demise of the thylacine is in some ways one of the best-documented and proven human-caused extinction events. Unfortunately, Tasmanian tigers were declared protected only two months before the last known individual died in captivity, too late for saving them from extinction,” says Marmol.
The shock is so strong that private initiatives have been taken to “stop extinction” aimed at resurrecting extinct species such as the Tasmanian tiger, the dodo bird or the woolly mammoth. So far – without success.
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“Although we remain skeptical about the possibility of actually recreating an extinct species by editing genes on living relatives of extant animals, we advocate more research on the biology of these extinct animal species,” says Marmol.