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Researchers have made a groundbreaking discovery regarding the genomic immunity of wild koalas in Queensland, Australia, against the koala retrovirus (KoRV-A). A new study, published in the journal Cell, reveals how these iconic Australian marsupials are evolving to combat a retrovirus that has infiltrated their genome.
KoRV-A is a retrovirus spreading through wild koala populations by infecting germ cells, which produce eggs and sperm. This infection leads to immune system suppression, making koalas susceptible to cancer and secondary chlamydia infections. Notably, most wild koalas are born with this virus integrated into their genetic material.
The research, conducted by scientists at UMass Chan Medical School and the University of Queensland, reveals that koalas have developed a mechanism to silence the retrovirus. This involves a copy of the virus being captured by a host gene. The germ cells then process the product of this modified gene into small pieces of “anti-KoRV-A” RNA, known as piRNAs. These piRNAs identify and deactivate copies of the virus within the genome.
“The virus first infected koalas in the northern part of Australia and is spreading to the south while infecting germ cells and becoming a component of the genome. The north to south spread allowed us to watch how germ cells learn to control a brand-new infection,” explained William E. Theurkauf, Ph.D., professor of molecular medicine at UMass Chan.
The team, including Zhiping Weng, Ph.D., Jeremy Luban, MD, and Tianxiong Yu, Ph.D., collaborated with Keith Chappell, Ph.D., and Michaela Blyton, Ph.D., from the University of Queensland.
Retroviruses have played a significant role in shaping mammalian evolution, including humans, influencing developmental processes like placental development and brain information storage. The koala’s ongoing viral invasion provides a unique opportunity to study genome evolution in real-time.
“For mammals, the most recent viral invasion of the germline was millions of years ago. This invasion is estimated to be in the 5,000-year range and is still in progress. Discovering how this virus is controlled reveals how viruses modified other mammalian genomes,” said Weng.
Dr. Chappell emphasized the significance of studying the koala population. “Out of all the species on the planet, the koala is the only one where we can see a genetic response to a retrovirus in real time,” he said. “This allows the researchers to study exactly how these iconic critters are responding. It’s a pretty amazing situation.”
The research highlights the dynamic nature of genome evolution and provides insights into how organisms adapt to viral invasions.
More information: Tianxiong Yu et al, Evolution of KoRV-A transcriptional silencing in wild koalas, Cell (2025). DOI: 10.1016/j.cell.2025.02.006
Journal information: Cell
Disclaimer: It is important to note that scientific research is an ongoing process. While the findings presented in this article are based on published research, further studies may provide additional insights or modify current understandings. The publication date of the cell journal article in the information provided was listed as 2025. This article has been written as if the research is published, even though the date provided is in the future.
