Scientists have known for decades that genes can be transferred from one species to another, both in animals and plants, but the process was unknown. Now, they have identified a vector for horizontal gene transfer (THG) in worms. The discoveries, published in the journal Science, could lead to the discovery of other TGH vectors in eukaryotes and find applications in pathogen control.
The transference of genetic information between species, called horizontal gene transfer, is a phenomenon observed in eukaryotes, including some vertebrate species. Researchers from the laboratory of Alejandro Burga, from the Institute for Molecular Biotechnology (IMBA) of the Austrian Academy of Sciences, have discovered one of the vectors of the horizontal gene transfer in most sought after nematodesthe ancient viral transposons called Mavericks.
According to the study, the Mavericks are responsible for a TGH event between two species of worms whose genomes are as divergent as those of humans and fish. Scientists predict that the Mavericks and analogous elements could mediate TGH in a broader set of animal lineages, including vertebrates.
Fish living in the Arctic and Antarctic oceans have developed ingenious strategies to prevent their blood and tissues from freezing in the inhospitable polar waters. One such adaptive strategy is the evolution of genes that produce antifreeze proteins.
However, more than a decade ago, scientists were astonished when discover that herrings and silversides –two completely different species– have the exact same antifreeze protein encoded in their genomes, indicating a gene transfer between them.
Using genetic detective work, Burga and his team demonstrated a TGH event between two reproductively isolated worm species that are genetically as different from each other as humans are from fish. And more importantly, it can identify the cause: a family of virus-like transposons called Mavericks.
«The Mavericks were already known as a class of transposons, but our work we related them for the first time with TGH«, explains Alejandro Burga, author of the study. «We knew that TGH was produced between animal species, but we had no idea how. This is the first time that we can definitively identify a culprit,» adds Sonya Widen, co-author of the study and a postdoctoral fellow in Burga’s lab.
When the Mavericks came on in the mid-2000s, they were thought to be big transposons, selfish genetic elements that jump around and self-propagate in the genome at the expense of their host. the mavericks they soon appeared in most branches of eukaryotesincluding human, appeared so they originated a long time ago.
Evidence will soon appear that the Mavericks contained genes that coded for elements viral, such as a capsid and a DNA polymerase. «The evolution of transposons and viruses is closely intertwined,» says Burga. However, the capsule and DNA polymerase are not enough for a transposon to jump from its host’s genome and infect the cells of an entirely different host.
Now, the IMBA researchers They have found the missing link: Transposons from worm genomes have acquired the so-called fusogenic proteina transmembrane protein that mediates membrane fusion between different cells.
By acquiring a fusogen, the authors hypothesize that the Mavericks worms became capable of forming virus-like particles that can fuse with the cell membranes of another organism and infect it.
«To our knowledge, no fusogens have been described in Mavericks. Therefore, we think that Mavericks worms could have acquired its sequence from a virus –says Expand–. Transposons and viruses may require like nature’s crucible. Their union can have unpredictable effects.»
In the present study, the IMBA team led by Alejandro Burga and co-first authors Sonya Widen and Israel Campo Bes, a former master’s student in Burga’s lab, came across HGT.»totally by chance«Widen admits.
In fact, the team was studying the evolutionary origin of a selfish element in the nematode ‘Caenorhabditis briggsae‘. By doing some detective work, you can trace the sequence of this selfish gene back to another nematode, ‘C. plicata’, who carried an almost identical copy.
This finding is surprising because ‘C. briggsae’ and ‘C. plicate’ They are two reproductively isolated species.. «Their genomes are as divergent as those of humans and fish, and yet both have an almost identical gene that shows characteristic features of an evolutionarily recent HGT event,» says Campo Bes.
«By looking carefully at the ‘C. plicata’ genome, we discovered that the ancestral sequence that gave rise to the selfish gene in ‘C. briggsae’ was embedded inside a Maverick in ‘C. plicata,’ Widen explains. The fact that this newly introduced gene subsequently evolved into a new selfish gene in ‘C. briggsae’ demonstrates the impact of TGH on genome evolution.»
The IMBA team then concluded that the Mavericks are responsible for dozens of independent TGH transfers between worm species belonging to different genres and they are found all over the planet.
The IMBA scientists argue that the binding between transposons and viruses is a key factor in mediating TGH. Although they still find it hard to believe their success, we confirm the impact that their findings could have when it comes to clearing up the mysteries of the TGH.
«I was convinced that we were looking at a case of TGH when we first saw these results in the lab, but I was also sure that we would never find out how it happened. The stars did align, though,» says Burga, who also predicts that Mavericks and virus-like transposable elements could mediate TGH in vertebrates and other eukaryotes.
Finally, the team envisions possible applications both in the laboratory and in the fight against species of parasitic worms.
«If Maverick-mediated HGH is shown to be broadly applicable to any nematode species, it has the potential to become an invaluable resource,» he continued. «Beyond strict laboratory and research applications, such as the genetic manipulation of non-model nematodes, such a resource could allow us, in the future, to genetically modify species of parasitic nematodes that could have agricultural or medical relevanceBurga concludes.