For the first time, scientists mentioned RNA from extinct animals!

Abstract: It is of great significance to the resurrection of extinct animals.

Author: Principle

Scientists have long been eager to extract RNA from ancient biological samples. But this wish is much more difficult than imagined. In September 2023, in a paper published in the journal Genome Research, researchers finally succeeded in extracting RNA from a specimen of an extinct animal, the Tasmanian tiger, and sequenced the RNA for the first time.

A specimen of the Tasmanian tiger collected in a museum. (Photo/Emilio Mármol Sánchez (photograph) and Panagiotis Kalogeropoulos.)

Extraordinary species

The thylacine (Thylacinus cynocephalus) was a carnivorous marsupial with a jaw that could open more than 80 degrees. It looked a bit like a dog, but because its tawny fur was partially covered with striped, tiger-like markings, it was also called the Tasmanian tiger.

As a ferocious animal at the top of the food chain, the Tasmanian tiger was once widespread in Australia. Unfortunately, in the 19th century, they were often hunted by humans. By the end of the 19th century, a bounty was offered for killing an adult Tasmanian tiger, which led to a continuous decline in the number of Tasmanian tigers. In 1936, the last known Tasmanian tiger died in a zoo in Tasmania, Australia.

DNA vs RNA

In recent years, some scientists have successfully mapped the genetic map of the thylacine. But these studies are based on DNA, not RNA. Like DNA, RNA can also carry genetic information and perform many other functions in organisms. But unlike the common double-stranded form of DNA, RNA usually exists in a single-stranded form. Relatively speaking, DNA is relatively stable, and scientists can extract ancient DNA from extinct ancient organisms that lived more than a million years ago; but RNA is not very stable, and there are many enzymes in nature that can break down RNA, which makes it extremely difficult to extract RNA from long-dead tissues.

Why do we need to extract RNA? This is because RNA can provide researchers with additional information about extinct species that has not been explored so far, such as different types of cells have different messenger RNAs, and RNA is also involved in the regulatory mechanisms of many genes.

RNA-seq

In the new study, the researchers analyzed a thylacine specimen stored in the Natural History Museum in Stockholm. The specimen had been stored at room temperature for more than a century. The researchers extracted three muscle samples and three skin samples, each weighing about 80 mg.

Given the age and state of preservation of the specimens, the researchers expected significant fragmentation of historical RNA sequences that might be present in the tissue matrix, so they used an RNA extraction protocol that targets small RNA molecules for each of the six tissue samples obtained.

The researchers extracted and purified 81.9 million and 223.6 million RNA fragments from these samples, respectively. After removing repetitive and very short sequences, they identified 1.5 million RNA sequences from muscle tissue and 2.8 million RNA sequences from skin tissue.

They also discerned differences between these tissue types based on the RNA in skin and muscle tissue. As expected, skin samples contained high levels of RNA associated with keratin (proteins found in skin, hair, and nails), while muscle samples contained high levels of RNA associated with myofibrillar proteins such as actin and myosin.

Significance

This is undoubtedly a remarkable achievement, as it is very difficult to extract ancient RNA, especially since this specimen was stored at room temperature rather than under sterile or frozen conditions. The results of this study have several important implications:

First, these findings have, to some extent, changed the way researchers look at the large number of specimens collected in museums;

Second, the researchers also detected traces of RNA viruses, opening the door to studying ancient viruses;

3. This study has injected new vitality into the development of ancient RNA sequencing technology. In the future, when ancient RNA technology becomes more and more mature, it will be possible to combine DNA and RNA sequencing to create a new era of ancient genetics;

4. The results of this study not only provide new clues to the biology of the Tasmanian tiger, but also have the potential to provide information for the resurrection of the Tasmanian tiger.

Although we cannot see extinct animals being resurrected in the short term, we can expect that in the near future, researchers will be able to extract RNA from mammoth samples from tens of thousands of years ago, which will bring new hope for the resurrection of mammoths.

This article is a work supported by Science Popularization China Starry Sky Project

Author: Principle

Reviewer: Ye Sheng, Professor of Beijing University of Aeronautics and Astronautics

Produced by: China Association for Science and Technology Department of Science Popularization

Producer: China Science and Technology Press Co., Ltd., Beijing Zhongke Xinghe Culture Media Co., Ltd.