Discovery of a type of immunity that protects koalas’ DNA from viruses hasimportance for the survival of koalas and our fundamental understanding ofevolution.

A team of scientists from The University of Queensland and University ofMassachusetts Medical School are studying tissue samples from koalas tounderstand how a unique type of cell responds to retrovirus infections, whichcause diseases such as chlamydia and cancer.

According to Dr Keith Chappell from UQ’s School of Chemistry and MolecularBiosciences, discovery of this unique immune system response could open awhole new field of research.

“The genomes of all animals, including humans, contain a large amount of viralsequences that are the result of infections that occurred millions of yearsago,” Dr Chappell said.

“The koala is the only species in which a retrovirus is known to have recentlyinfected the germline cells – the ones that make sperm and eggs.

“This means that some koalas are born with koala retrovirus A – known asKoRV-A – in their genome, making them more susceptible to diseases suchchlamydia and cancer.”

It is well known that viruses have driven the evolution of humans and animalsover thousands of years, yet understanding how germline cells respond toinfection has been a mystery for scientists.

“It was previously thought that the process of natural selection kept levelsof viral elements in check within the genome, meaning that it would besurvival of the fittest for the koala,” Dr Chappell said.

“However, our findings show that there are immune response like pathwayswithin a koala’s germline cells that can actively fight back against theinvading virus.”

Professor William Theurkauf from UMass Medical School said the germline cellsof koalas could distinctly recognise the unique sequence of KoRV-A as an“invading virus” and not a gene, and would mount an initial defence.

“Just like the human body launches an immune response to invading viral andbacterial infections, our findings suggest that germline cells mount an attackto chop up the viral sequences,” Professor Theurkauf said.

“This prevents the retrovirus from inserting more and more copies into thegenome of the offspring and thereby protects the next generation against whatwould be compounded effects of disease.”

The research findings are published in Cell (DOI:10.1016/j.cell.2019.09.002).

The study was supported through funding from the USA’s National Institute ofHealth, the Australian Research Council and the Chinese National NaturalScience Foundation.

Image: Discovery of koalas’ unique immune system response could open a wholenew field of research

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