Eight percent of your genome derives from retroviruses that inserted themselves into human sex cells millions of years ago. Right now the koala retrovirus (KoRV) is invading koala genomes, a process that can help us understand our own viral lineage and make decisions about managing this vulnerable species.
In a recent study, published in Molecular Biology and Evolution, scientists from the University of Illinois discovered that 39 different KoRVs in a koala’s genome were all endogenous, which means passed down to the koala from one parent or the other; one of the KoRVs was found in both parents.
Koalas are the only known organisms where a retrovirus is transitioning from exogenous to endogenous. An exogenous retrovirus infects a host, inserts its genetic information into the cell’s DNA, and uses the host cell’s machinery to manufacture more viruses. When an exogenous retrovirus infects an egg or sperm cell and the viral genetic information is then passed down to the host’s offspring, the virus becomes an endogenous retrovirus (ERV).
Becoming part of the koala genome
Like humans, koalas have evolutionary defenses against endogenization.
“During the early stages of endogenization, there are huge numbers of retroviruses. KoRVs are present all across koalas’ genomes, with many thousands or tens of thousands of KoRVs in the population,” said Alfred Roca, a Professor of Animal Sciences and member of the Institute for Genomic Biology at the University of Illinois at Urbana-Champaign. “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.”
In order to end up with 100 ERVs in an organism, the species may have to start with 10,000 ERVs in its ancestors, Roca said. 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.
The ERVs that are successfully passed down are protected by the koala’s DNA repair mechanisms so that their rate of mutation is extremely low. Based on the dearth of mutations in the endogenous koala retroviruses, Roca’s team was able to estimate that the KoRVs integrated into the host germ line less than 50,000 years ago. “This is quite recent compared with other ERVs that are millions of years old and have accumulated mutations,” said first author Yasuko Ishida, a research specialist in Roca’s lab.
Overcoming retroviral fitness effects
In koalas, KoRV has been linked to leukemia, lymphoma, and immune suppression, which can lead to increased susceptibility to chlamydia.
“It seems likely that for thousands of years since this virus integrated, the koala host has suffered fitness effects,” Roca said. “It is possible that across species, when a host lineage has been invaded by ERVs, it had to go through this process of adaptation between host and virus, which is a very sad finding. It may be a very long, slow, painful process for the host species, one which human ancestors have gone through and overcome many times in the distant past.”
In mammals, retroviral DNA is associated with placental development and has been found to protect hosts from harmful exogenous retroviruses.
“But once retroviruses become part of the host, they begin to help the host because that is how they survive,” Roca said. “They will be better off if they evolve to protect the host. Over time, the detrimental effects go down and the beneficial effects go up.”
Conserving koala populations
In the 1900s, koalas were extensively hunted for their fur. In an effort to preserve koalas, a few individuals were moved to an island off the coast of Australia. Years later, the inbred island population was reintroduced to southern Australia. Today some of the southern koalas remain uninfected while almost all northern koalas have dozens of KoRVs in their genomes.
“Which is the lesser of two evils?” Roca said. “Do you try to conserve genetic diversity, which is present in the northern populations along with the retrovirus or do you conserve southern populations that don’t have the retrovirus but are horribly inbred?”
Roca’s research team included research specialist Yasuko Ishida, graduate student Kai Zhao, and scientific collaborator Alex Greenwood of the Leibnitz Institute in Berlin. Their work was supported by the National Institute of General Medical Sciences. The San Diego Zoo, Columbus Zoo, San Francisco Zoo, and Riverbanks Zoo provided the koala samples.
Written By: Claire Sturgeon. Photos by Kathryn Coulter and Yasuko Ishida
Nicholas Vasi | EurekAlert!
Toward a 'smart' patch that automatically delivers insulin when needed
18.01.2017 | American Chemical Society
127 at one blow...
18.01.2017 | Stiftung Zoologisches Forschungsmuseum Alexander Koenig, Leibniz-Institut für Biodiversität der Tiere
Yersiniae cause severe intestinal infections. Studies using Yersinia pseudotuberculosis as a model organism aim to elucidate the infection mechanisms of these...
Researchers from the University of Hamburg in Germany, in collaboration with colleagues from the University of Aarhus in Denmark, have synthesized a new superconducting material by growing a few layers of an antiferromagnetic transition-metal chalcogenide on a bismuth-based topological insulator, both being non-superconducting materials.
While superconductivity and magnetism are generally believed to be mutually exclusive, surprisingly, in this new material, superconducting correlations...
Laser-driving of semimetals allows creating novel quasiparticle states within condensed matter systems and switching between different states on ultrafast time scales
Studying properties of fundamental particles in condensed matter systems is a promising approach to quantum field theory. Quasiparticles offer the opportunity...
Among the general public, solar thermal energy is currently associated with dark blue, rectangular collectors on building roofs. Technologies are needed for aesthetically high quality architecture which offer the architect more room for manoeuvre when it comes to low- and plus-energy buildings. With the “ArKol” project, researchers at Fraunhofer ISE together with partners are currently developing two façade collectors for solar thermal energy generation, which permit a high degree of design flexibility: a strip collector for opaque façade sections and a solar thermal blind for transparent sections. The current state of the two developments will be presented at the BAU 2017 trade fair.
As part of the “ArKol – development of architecturally highly integrated façade collectors with heat pipes” project, Fraunhofer ISE together with its partners...
At TU Wien, an alternative for resource intensive formwork for the construction of concrete domes was developed. It is now used in a test dome for the Austrian Federal Railways Infrastructure (ÖBB Infrastruktur).
Concrete shells are efficient structures, but not very resource efficient. The formwork for the construction of concrete domes alone requires a high amount of...
10.01.2017 | Event News
09.01.2017 | Event News
05.01.2017 | Event News
18.01.2017 | Power and Electrical Engineering
18.01.2017 | Materials Sciences
18.01.2017 | Life Sciences