Reveal the influence of viruses
- Viruses acquire genes from eukaryotes – organisms whose cells store their DNA in a nucleus – and use them for their own function.
- Conversely, eukaryotes acquire genes from viruses to bring new functions to their cells, even antiviral defense in mammals.
- Gene exchange between viruses and eukaryotes is a key evolutionary driver causing cellular innovation and long-term change in organisms.
To classify all living organisms, scientists use taxonomy – a naming system – to group similar organisms together. Larger groupings are called kingdoms. For example, humans, all animals, plants, fungi, and multicellular organisms are members of a kingdom called eukaryotes.
Eukaryotic cells all have one important thing in common: they house their DNA in a nucleus. The cell nucleus is centrally located and bound to the membrane.
Prokaryotes include bacteria and archaea, single-celled organisms whose DNA is loose and surrounded by a cell membrane.
Viruses are even simpler. They consist of only DNA or RNA and have only one protective layer of protein, called the capsid, that surrounds them.
What do these distinct organisms have to do with each other and with evolution? Quite a bit, according to Oxford University evolutionary biologist and first author of the new study, Dr Nicholas AT Irwin.
Viruses and eukaryotes depend on each other. The former use their host-derived genes for cell replication and control, often coding for cell-derived informational and operational genes that allow viruses to adapt and survive.
Eukaryotes can incorporate viral DNA into their genomes. This new DNA, previously thought to be inactive, has now been shown to provide new functionality to their eukaryotic hosts.
Colleagues from the Department of Botany at the University of British Columbia in Vancouver, Canada, and the Department of Zoology at the University of Oxford, UK, collaborated with Dr Irwin to reveal groundbreaking findings on the movement of genes between viruses and eukaryotes, called the horizontal gene. transfer.
In the review
Using well-established computational analyzes of evolutionary development and species diversification, called phylogenetics, the researchers were able to determine how bidirectional gene transfers from viruses and eukaryotes drove species diversification.
Dr Irwin explained to Medical News Today that the researchers “used computational analyzes to search for evidence of transferred genes in the genomes of approximately 200 eukaryotes and thousands of viruses, which spanned the diversity of eukaryotic and viral species whose genomes had been sampled.”
“We were not only interested in identifying viral genes in eukaryotic genomes, but also in detecting the presence of eukaryotic genes in viral genomes.”
Medical News Today asked Dr Irwin how they had come to such drastic conclusions about the genetic relatedness between eukaryotes and viruses. Dr Irwin said:
“One of the important factors that allowed us to conduct this analysis was the huge amount of genomic data now available on eukaryotes, viruses and prokaryotes (including bacteria and archaea). These new resources are the result major DNA sequencing efforts aimed at understanding the diversity of genomes across the tree of life.
“In addition to this, recent technological advances in high-throughput DNA sequencing and metagenomics, which is the sequencing and assembly of genomes of mixed communities of organisms, such as seawater samples, have accelerated the rate at which this data has become available.”
“Having a wide diversity of high-quality genomic datasets was crucial, as it allowed us to infer which species were participating in these gene transfers,” Dr Irwin added.
Scientists have found that viruses and eukaryotes “hijack” other people’s DNA.
But, they found that eukaryotic genes were transferred to viruses about twice as frequently as viral genes transferred to eukaryotes.
Dr Irwin explained that there could be several reasons why viruses were the big winners in genetic competition. He noted that genes can frequently be transferred from virus to eukaryote, but might not stay due to natural selection.
But, viruses can keep the genes they acquire from their hosts because they are beneficial to the virus. And, for a gene to persist, the organism must survive and spread, a trait at which viruses are very adept.
The researchers then applied all their knowledge of the genetics of these many eukaryotes and viruses and compared them to well-established evolutionary trees. This way, they could approximate the timing of gene transfer events relative to when species diverged or specified, meaning becoming a new type of species. For Medical News Today, Dr Irwin illustrated:
“If we observed a viral gene in a human genome, we would predict that the gene was acquired after humans differentiated from other primates. In contrast, if a viral gene was present in all animals, say from sponges to chimpanzees, we would infer that this gene was derived from the animals’ last common ancestor.
“Of course, there are different ways to interpret these patterns, but we base our interpretations on the assumption that obtaining a gene by gene transfer is more difficult and unlikely than losing a transferred gene. “
[D]r. Irwin described three distinct incidents in evolution where viral genes are present and illustrate virus-influenced evolution:
- Animal genes are involved in the production of hyaluronic acid, an important component of animal tissues.
- Trypanosome parasites, the causative agent of sleeping sickness and Chagas disease, possess several viral genes in their mitochondria.
- Viral genes are present and appear to function in placental development, indicating that these genes may have contributed to the evolution of placental mammals.
Medical News Today asked Dr. Irwin what intrigued him most about his results. He thinks,
“The most exciting outcome of the study was being able to identify and visualize patterns of gene transfer across the eukaryotic tree of life.”
“One of my main interests is to understand how cellular diversity and complexity evolved, and I believe this work has provided strong evidence that host-virus interactions played an important role in generating cell diversity. the life we see today.”
“I also think this study has some interesting implications for how we perceive viruses. Similar to how the discovery and characterization of the microbiome has changed our view of bacteria, I think revealing the influence viruses have had on the evolution of life could encourage more nuanced thinking about the importance of viruses. in nature.
– Dr. Irwin
Regarding where this research could lead to future scientific endeavours, lead author Professor Patrick Keeling added: “Many advances in understanding [h]Orizontal gene transfer (HGT) in eukaryotes focused on the pattern of gene transfers on the eukaryotic tree – we now also have insight into the process that led to this pattern and the likelihood that viruses are a major route of transfer.
“It would be helpful to take some of the lineages where we see a lot of viral HGT and dig deeper, looking at more closely related hosts and viruses to see the process unfold on different time scales.”
And finally, Dr. Keeling noted, “identifying selected genes in viruses can tell you a lot about the process that makes the virus more efficient and, by extension, how it uses its host cell.”
This study, explaining the HGT between eukaryotes and viruses, is the first of its kind to reveal how viruses may have allowed multiple eukaryotic species to diverge and evolve.