Koalas Shed Light on Human Genome?

Koalas aren't exactly closely related to humans, but these furry animals are helping to shed light on the human genome, according to a new study.

Eight percent of our genome derives from retroviruses, or RNA viruses, that inserted themselves into human sex cells millions of years ago. And right now the koala retrovirus (KoRV) is invading koala genomes, a process that can help us understand our own viral lineage.

There are two types of retroviruses: exogenous, in which the virus infects a host and uses its DNA to replicate, and endogenous - meaning the retrovirus infects an egg or sperm and passes its genes down to the host's offspring.

According to the study, 39 different KoRVs in a koala's genome were all endogenous, proving it as the first organism known to transition from exogenous to endogenous retrovirus (ERV). It's possible that thousands or even tens of thousands of KoRVs are in the population, but koalas have evolved ways of combating these viruses, which can lead to several conditions like leukemia, lymphoma and immune suppression.

"Over time most of them will disappear because these copies of the virus may be present in as few as one individual chromosome. If that one individual happens to not reproduce, or if it reproduces and the other chromosome is passed down, then that ERV will disappear," researcher Alfred Roca explained in a statement.

Humans too have developed evolutionary defenses against endogenization. Learning how Australia's iconic marsupial came to live with retroviruses could help scientists understand the same process occurred in humans.

Home Sweet Home

It takes retroviruses, like KoRV, many thousands of years to become a fixed part of the koala genome, like the eight percent of retroviral DNA that all humans share. This process can often be devastating for whatever species finds itself the victim. However, the silver lining is that over time, as retroviruses get comfortable in the host, "the detrimental effects go down and the beneficial effects go up," Roca said.