Virus Attacking Koala
The virus, called Koala Retrovirus (KoRV), is linked to cancer, weakened immunity, and chlamydia infection in koalas
A virus that infects koalas is steadily integrating itself into their DNA, ensuring that it survives from generation to generation. But the koala genome is defending itself. This reveals that DNA has an immune system to shut down invaders.
All retroviruses hijack the DNA in some cells of their host’s body, but few manage to get transmitted to the host’s offspring.
Retroviral sequences can contribute to disease, but have also been co-opted by the host animals for processes that are essential to healthy development. As much as eight percent of the human genome is made up of the remnants of infectious viruses.
Retroviruses have frequently appeared during evolutionary history. Though we have little information about how retroviral sequences infiltrate sperm and egg cells, or how these cells react.
Virus Attacking Koala- The Vintage Retrovirus
It is known that almost all known retrovirus genome invasions happened millions of years ago. However, Koala Retrovirus is a recently identified exception. This retrovirus spreads between individuals but is also infecting sperm and egg cells. Consequently, many koalas are born with this pathogen as part of their genome.
Scientists
at the University of Queensland are collaborating with their colleagues from the University of Massachusetts Medical School to analyze how koala sperm and egg cells respond to koala retrovirus KoRV-A infection.The findings suggested that these cells mount a novel- “innate genome immune response” to viral infection, which may help control the spread of infectious KoRV. During the project, the team analyzed DNA and RNA from different tissue samples from deceased wild koalas from South East Queensland.
The team of scientists specifically looked for short sequences of RNA, between 23 and 35 nucleotides long, known as PIWI Interacting RNAs (piRNAs).
Virus Attacking Koala- An Immune System For The Genome
Scientists found that there is a specialized immune system to defend against retroviral genome invasion. Like the conventional immune system, this one includes an innate response that is generalized. It also contains the adaptive response, which learns to recognize specific pathogens and eliminate them.
At the early stages of egg or sperm infection, the altered DNA sequence results in a specific molecular pattern that is recognized by an innate genome immune system. This stops the activity of the virus and starts producing signature piRNA sequences to identify the invader.
The innate immune response works until the memory of the genome invader is created, and a sequence-specific adaptive response kicks in.
This “genome immune system” changes our understanding of what shapes the genomes of all animals.
