For the first time, geneticists have retrieved and decoded the RNA (ribonucleic acid) from an extinct animal. Scientists isolated the RNA from a 130-year-old Tasmanian tiger (or thylacine) specimen at the Swedish Museum of Natural History.
The research team sequenced RNA from the skin and skeletal muscle of the thylacine. Though most of the RNA was similar to that of modern-day marsupials, the thylacine’s closest living relatives, some was different. “We discovered a thylacine-specific microRNA isoform that we could not have confirmed without RNA evidence,” the team announced.
A step up from extracting DNA
What makes this study groundbreaking is the extraction of RNA over DNA. DNA is regularly extracted from fossils, however, extracting RNA is a breakthrough. RNA carries genetic information and tells us far more about the organism than DNA. It takes the instructions from DNA and puts them into practice, synthesizing proteins and regulating cell metabolisms.
Looking at the RNA, “gives you the amount, the diversity, and the effectiveness of the [DNA] within the biology of the cell,” co-author of the study Emilio Mármol Sánchez explained. “RNA sequencing gives you a taste of the real biology and metabolism regulation that was happening in the cells and tissues of Tasmanian tigers before they went extinct.”
A thylacine on display in a museum. Photo: Shutterstock
Isolating RNA from ancient samples is incredibly difficult. Unlike DNA, RNA exists as a single strand of genetic material, rather than a double strand. It is far less stable and can break down rapidly. Researchers had to adapt their RNA extraction method so they could use it on an older sample. They extracted 81.9 million RNA fragments from the thylacine’s muscle and 223.6 million from the skin. After eliminating duplicates and short sequences, they were left with 2.8 million fragments from the skin and 2.5 from the muscle tissue.
Driven to extinction by humans
The demise of the thylacine is well documented. The wolf-sized marsupial was an apex predator, but around 2,000 years ago it disappeared from the Australian mainland and only clung on in Tasmania. European settlers hunted them to near extinction in the 18th century because they were a threat to livestock and the last known individual died in a Tasmanian zoo in 1936. Since then, many naturalists have tried and failed to find a hidden population of the animals in Tasmania’s forests.
Some scientists are also planning to bring the thylacine back from extinction. Though the two projects are unconnected, the RNA study should be incredibly useful to those hoping to resurrect the species. It provides insight into the species’ genetic makeup, the gene expression of different tissues within the animal, and viruses that may have affected the species.
“This will add significant depth to our understanding of the biology of extinct animals and help us to build much better extinct genomes,” said Andrew Pask, who is leading the team trying to resurrect the thylacine.
