Koalas have suffered throughout the years, from habitat destruction, dog attacks, car accidents. But that's only the explicit stuff, they have been plagued by chlamydia and many cancers, like leukemia and lymphoma. As scientists researched these problems, they found a natural laboratory in which they can study one of the most controversial topics in biology: how viruses can insert themselves into animal's DNA and at times change the course of evolution. The target of this research project is the Koala retrovirus (KoRV), a segment of protein and genetic material in the same family as H.I.V, it began inserting itself into the koala genome about 40,000 ago and is currently passed down generations. It can also be transmitted between species, as a viral infection. Recently scientists have found that the insertion of viruses into animal genomes many times through evolution. It is estimated that 8% of the human genome is made up of viral left overs from previous infections, this occurred millions of years ago, many of them occurring in primate ancestors before the existence of humans. KoRV is peculiar because 40,000 years ago was an important period in evolutionary time, and because the process keeps occurring. A group of scientists reported they observed a genome immune system fighting to render the virus inactive now that has established itself in the Koala DNA. They also reported that KoRV might have activated other ancient viral DNA. This activity stirs the pot of mutation and variation that is essential for natural selection. William Therkauf, a professor in molecular medicine at the University of Massachusetts Medical School, says that "Koala genetics are a gold mine, what they are going through is the process of what's driven the evolution of every animal on the planet". Previous viral infections have led to major evolutionary changes, he said for example: “A gene that is absolutely essential for the placenta was derived from the shell of a virus millions of years ago.” humans wouldn't exist without that specific retroviral infection. When the viral RNA infects a cell, it takes over the DNA machinery and replicates itself, which keeps the process going. This process is what causes diseases like AIDS, the most known retroviral disease. However, when the insertion of the retrovirus occurs in a sperm or egg cell, the changes become permanent, kept forever. When retroviruses become part of an animals DNA, they are called endogenous and eventually no longer cause the same type of original infection they once did. But they can still be used for other purposes, like making placenta. “It was long thought they were just junk DNA,” said Shawn L. Chavez, a molecular biologist at the Oregon Health and Science University School of Medicine in Portland, who wrote a review of research on endogenous retroviruses in mammals. Now it is clear that some of them have changed the course of evolution. Exactly how is what scientists are trying to find out. “It seems like there’s a new publication every day,” she said.
Consequently, koalas are drawing a lot of attention from scientists who did not start out with an interest in the animal or its conservation. “I’m a fruit fly guy,” Dr. Theurkauf said. He became interested after a reading a report in 2006 by Rachael Tarlinton of the University of Nottingham and other scientists about the invasion of the koala genome by the retrovirus. Dr. Tarlinton began her career in Australia as a veterinarian with an interest in infectious diseases in wildlife. She became involved in the study of koala genetics because of the big issue of chlamydia and because Jon Hanger, an independent researcher, had noticed very high death rates from leukemia and other cancers in koalas kept in zoos. Their research led to the discovery that koala retrovirus was causing some cancers, and that it was not only infecting the animals but also part of their genome. Dr. Tarlinton and her colleagues established the presence of the retrovirus in koalas in Queensland, however there is another, a southern population of koalas that at first seemed not to have the virus. These koalas also had fewer chlamydia infections. The genetics of the population in the south are different because most koalas in that region had been killed for the fur trade by the 1920s. Only a few them survived by being moved to small islands at the beginning of the 20th century. From that population, they have been reintroduced and those koalas have done extraordinarily well, even though they have a few genetic problems. There are over 10, 000 of them, in some areas they even have been killed to keep the population down. The researchers expected the southern koalas to be less healthy overall than the northern ones but it was the other way around.
A closer look at the southerners’ DNA showed that they weren’t free from the inherited retrovirus as it was thought. The virus was there but it was damaged. The beginning and end of its genetic code were present, but the middle was missing. A report on this work is now in bioRxiv, an online database for papers that have been written but not yet accepted by claimed journals. It is thought that the missing segment could be the key to saving the koala population, this defective version can be protective. Dr. Tarlinton are planning an experiment, in which there are cells lines which can grow KoRV, then the defective version can be inserted, ans study the cells to determine if the full virus can successfully infect or inhibit the cells. Dr. Theurkauf and his colleagues found that in koalas there appears to be an initial first-line genome defense involving the piRNA snippets that responds to any virus trying to jump around the genome. Then, a more specific response built to a particular virus comes into play. This is something they want to test further, by looking at koalas in different populations. Dr. Theurkauf and his colleagues also discovered other intriguing clues to what happens as viruses become part of an animal’s DNA. “One thing that we found that is really curious,” Dr. Theurkauf said, is that koalas also have ancient retroviruses that became part of the genome millions of years ago and were presumably deactivated long ago. But at least four of them are just as active as koala retrovirus. They are moving around the genome. “KoRV may be activating these dormant old viruses. It may really stir the pot.” “It’s evolution in real time,” he said.
This is extraordinary to me, its evolution right in front of us, I believe in studying populations of animals and hope to do so in the future. This article was interesting to me because it gathered different scientists from different fields to study this phenomenon. I have been looking more and more into these experiments and I think this is a giant breakthrough in evolutionary and genetic biology. This will help us discover more about how retroviruses work and save the koala population which has previously had many issues perishing.
https://www.nytimes.com/2019/10/10/science/koala-retrovirus-evolution.html
