By Will Dunham
(Reuters) – The Tasmanian tiger, a dog-sized striped carnivorous marsupial also called a thylacine, once roamed the Australian continent and adjacent islands, an apex predator that hunted kangaroos and other prey. Because of man the species is now extinct.
But that doesn’t mean scientists have stopped studying it. In a scientific first, researchers said Tuesday that they have recovered RNA – genetic material found in all living cells that has structural similarities to DNA – from the dried skin and muscles of a Tasmanian tiger preserved since 1891 in a Stockholm museum.
In recent years, scientists have extracted DNA from ancient animals and plants, some dating back more than 2 million years. But this study marked the first time that RNA – much less stable than DNA – had been recovered from an extinct species.
While not the focus of this research, the ability to extract, sequence, and analyze old RNA could spur other scientists’ efforts toward recreating extinct species. Recovering RNA from old viruses could also help decipher the cause of past pandemics.
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 the genetic information it receives from DNA, putting this information into practice. RNA synthesizes the panoply of proteins that an organism needs to live and works to regulate cellular metabolism.
“RNA sequencing gives a glimpse into the true biology and regulation of metabolism that occurred in the cells and tissues of Tasmanian tigers before they became extinct,” said geneticist and bioinformatician Emilio Mármol Sánchez of the Center for Paleogenetics and SciLifeLab in Sweden, lead author of the study published in the journal Genome Research.
“If we want to understand extinct species, we need to understand what genetic complements they have and also what the genes were doing and which ones were active,” said geneticist and study co-author Marc Friedländer of Stockholm University and SciLifeLab.
The question was how long the RNA could survive in the kind of conditions – room temperature in a cupboard – in which these remains had been stored. The remains preserved at the Swedish Museum of Natural History were in a semi-mummified state, with skin, muscles and bones preserved but internal organs lost.
“Most researchers thought that RNA would only survive for a very short time – like days or weeks – at room temperature. This is probably true when samples are wet or moist, but apparently not the case when they are dried “said the evolutionary geneticist. Love Dalén of the Center for Paleogenetics.
The Tasmanian tiger resembled a wolf, except for the tiger-like stripes on its back. The arrival of humans in Australia around 50,000 years ago led to massive population losses. The arrival of European colonizers in the 18th century spelled doom for the remaining populations concentrated on the island of Tasmania, with a bounty subsequently placed on them after they were declared dangerous to livestock. The last known Tasmanian tiger died in a Tasmanian zoo in 1936.
“The story of the disappearance of the thylacine is in some ways one of the most well-documented and proven human-induced extinction events. Sadly, Tasmanian tigers were declared protected only two months before the last known individual died in captivity, too late to save them from extinction,” Mármol said.
Private “de-extinction” initiatives have been launched to resurrect some extinct species such as the Tasmanian tiger, the dodo or the woolly mammoth.
“Although we remain skeptical about the possibility of actually recreating an extinct species using gene editing on existing living animal relatives – and the time frame to get to an end point may be underestimated – we support further research into the biology of these extinct animals. “Mármol said.
(Reporting by Will Dunham in Washington, Editing by Rosalba O’Brien)