Why did the Tasmanian Tiger go extinct? RNA extraction procedure explained

According to several reports, it is believed that the last known Tasmanian Tiger took its last breath back in 1936 in the Beaumaris Zoo in Hobart, Tasmania. As the animal was hunted, its habitat was destroyed and it had to face the introduction of fatal new diseases until its demise. It was even considered a pest with a bounty placed on its head in 1888.

However, the successful RNA recovery from a 132-year-old specimen has scientists believing that the extinct Tasmanian Tiger could once again walk the earth. The research paper regarding the extraction process was published in Genome Research last week as a collaborative study between the Centre for Palaeogenetics and SciLifeLab researchers.

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The tragedy of the Tasmanian Tiger

The Tasmanian Tiger, also known as the Thylacine, was once native to the Australian islands of New Guinea and Tasmania and was present in the mainland. The animal went extinct in New Guinea and the Australian mainland over 300 years ago, with researchers assuming that it died out due to competition from the introduction of the dingo and climate change.

However, the carnivorous marsupial still survived on the Tasmanian island. This was put to a halt with the arrival of European colonizers in Australia. According to the book by David Owen, titled Thylacine: The Tragic Tale of the Tasmanian Tiger, there were around 5,000 of these tigers living on the island at the time.

Colonizers did not take kindly to the animals as they considered the Thylacines a threat to their sheep and other livestock. This led to a massive hunting spree of the animals, which was fully supported by the government as well. The earliest recorded bounties for the animal date back to 1830.

In 1888, £1 was offered by the Tasmanian government for the confirmed killing of a full-grown adult Tasmanian Tiger, along with 10 shillings being offered to get rid of the pups. This hunting spree, along with other factors such as lack of genetic diversity due to isolation from the mainland, the introduction of the fatal marsupi-carnivore disease, and habitat erosion, led to its extinction from Tasmania.

In 1936, the last documented Thylacine died in the captivity of the Beaumaris Zoo in Hobart, Tasmania, due to suspected neglect. The species was officially declared extinct by the International Union for Conservation of Nature in 1982 and later in 1986 by the Tasmanian government.

However, a paper published in the Science of the Total Environment in March 2023 documented and analyzed unconfirmed sightings of the animal from 1910 to 2019, which were based on various public accounts of sightings, concluded that there was a small possibility that the animal may have lived up to the 2000s. However, the publication was based on public sighting accounts, which is why the information is still without concrete evidence.

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RNA extracted from 132-year-old Thylacine specimen suggests a significant step towards the resurrection of extinct organisms

In September 2023, a study published in Genome Research concluded that a team of Swedish-Norwegian scientists successfully recovered RNA from a 132-year-old Tasmanian Tiger specimen. This was used from the Stockholm Natural History Museum and was preserved at room temperature.

RNA has structural similarities to DNA, but they're not the same. Ribonucleic Acid, or RNA, is a single-stranded nucleic acid present in every living cell. There are three kinds of RNA, one that houses genetic blueprint to make proteins (mRNA), another that translates the mRNA to proteins (tRNA), and another that forms ribosomes, which is useful for protein synthesis (rRNA).

Lead author of the study, Emilio Mármol, said:

"RNA sequencing gives you a taste of the real biology and metabolism regulation that was happening in the cells and tissues of the Tasmanian tigers before they went extinct."

In this case, the RNA was sequenced from the skin and skeletal muscle tissues of the Tasmanian Tiger specimen, which formed what is known as the organism's transcriptome. The quality of the recovered transcriptomes was so good that muscle- and skin-specific protein-coding RNAs were able to be identified.

Recovered RNA sequences revealed how the muscles of the organism stretched and contracted along with information on the outer layer of skin, including the hair and nails. Emilio Mármol, who was also a computational biologist at Sweden's Centre for Palaeogenetics and SciLifeLab, said in a press release:

"Resurrecting the Tasmanian tiger or the woolly mammoth is not a trivial task, and will require a deep knowledge of both the genome and transcriptome regulation of such renowned species, something that only now is starting to be revealed."

Although no animal in history has ever been brought back from extinction, the successful extraction and sequencing of RNA molecules, especially using museum specimens, represents a significant step towards the resurrection of extinct organisms.