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Study uncovers retroviruses are at least 450 million years old
New evidence presented in Nature Communications revealed that retroviruses are several hundred million years older than previously thought, indicating they have been with their animal hosts through the evolutionary transition from sea to land.
“Very little has been known about the ancient origin of retroviruses, partly because of the absence of geological fossil records,” Aris Katzourakis, PhD, from the department of zoology at Oxford University, said in a press release. “Retroviruses are broadly distributed among vertebrates and can also transmit between hosts, leading to novel diseases such as HIV, and they have been shown to be capable of leaping between distantly related hosts such as birds and mammals.”
Retroviruses, from the same virus family as HIV, can cause cancers and immunodeficiencies in a variety of animals. The researchers used genome sequences from endogenous retroviruses — retroviruses that originate internally — that resemble what are known as the ‘foamy’ viruses. Because these ‘foamy’ viruses, which diverge alongside their hosts, are widespread in mammals, the investigators unearthed genomic fossils for previously unknown foamy-like retroviruses in various hosts, such as ray-finned fish and amphibians.
The researchers discovered 36 lineages of basal amphibian and fish foamy-like endogenous retroviruses (FLERVs). Using phylogenetic analyses, they observed an overall co-speciation pattern between the ray-finned fish FLERVs and their hosts. Investigators detected several possible ancient viral cross-class transmissions, involving lobe-finned fish, shark and frog FLERVs. Sequence examination uncovered two major lineages of ray-finned fish FLERVs, one of which had gained two new accessory genes within their extraordinary large genomes.
The rapid evolution of viruses often obscures their early history, but the researchers used a recently developed approach along with the genomic fossil records of the foamy-like viruses, which slowed down the rate in evolution the further back they explored. Proven by the phylogenetic analyses, the findings suggest retroviral lineage have an ancient marine origin that began with, if not before, their vertebrate hosts almost half a billion years ago.
“We need to consider the adaptations that vertebrates have developed to combat viruses, and the corresponding viral countermeasures, as the product of a continuous arms race that stretches back hundreds of millions of years,” Katzourakis said in the release. “Our inferred date of the origins of retroviruses coincides with the origins of adaptive immunity, and thus it is likely that retroviruses have played an important role in the emergence of this key tool in vertebrate antiviral defense.
“As we understand the nature of the interaction between viruses and host immunity, we will be better placed to intervene in this delicately balanced arms race in order to develop novel treatments and interventions.” – by Savannah Demko
Disclosure: Katzourakis reports no relevant financial disclosures.