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Biologists have found that some genetic factors with viral characteristics may be the cause of gene transmission between different species.

(by Chen Qiang / tr. by Robert Taylor)

Biologists have roughly figured out the laws of heredity for more than a century: genes are passed from parents to children within the same species. But in recent years, biologists have also realized that some genes can violate this law and can be transmitted across different species.

Can genes be transmitted across species? For example, herring and cucumber fish are two different types of fish that live in cold waters, but they both have almost identical antifreeze genes and can express proteins that prevent blood from freezing. Biologists speculate that the gene is likely to be passed from herring to cucumber fish. In addition, in the tropical rainforest of Madagascar, biologists were surprised to find that a gene called "BovB" in the genome of local frogs seems to have originated from snakes.

These phenomena are called horizontal gene transfer (horizontal gene transfer). Biologists have been confused about the mechanism behind it, although they suspect that the virus plays a role.

In a recent paper published in the journal Science, biologists at the Austrian Academy of Sciences say they have found a class of transferable genetic factors that can carry certain genes and transfer between different species of nematodes.

Moving from one nematode to another may not sound like a big deal, but these nematodes have been differentiated for hundreds of millions of years, and the difference between them is the same as that between fish and humans.

These genetic factors, called "Maverick", are detected in a variety of animals, including invertebrates and vertebrates, and have the characteristics of many viral genes. Considering these properties, biologists suspect that Maverick and similar genetic factors may contribute to horizontal gene transfer in the evolution of life.

The new discovery from nematodes stems from the study of a unique genetic factor in the nematode genome. This genetic factor is so selfish that it can even kill offspring that do not carry it. It contains two genes, one expressing a toxic protein and the other expressing an antidote that neutralizes the protein.

A nematode that carries this genetic factor produces eggs or sperm that deposit toxins. Only in fertilized eggs can genetic factors normally express antidotes. In this way, if the nematode mated with an individual who did not carry the genetic factor, only the offspring who inherited at least one copy of the genetic factor could express the antidote and survive. It's as if genetic factors use this "toxin-antidote" combination to hijack the nematode genome to ensure its transmission.

In 2021, biologists at the Austrian Academy of Sciences found that the toxin gene in one nematode looked almost identical to a different functional gene in another nematode, with a nucleotide similarity of almost 97%. It's as if the gene was copied from one kind of nematode and then pasted into the genome of another in some way.

Virus-like genetic factors in order to reveal the source of the problem, biologists decided to check the surrounding DNA. They found repetitive sequences in the DNA on both sides of the gene, much like part of the transposon. Transposons are genetic factors that can move within a genome and insert their own copies into different parts of the genome by copying themselves.

The team also found residues of several viral genes on both sides: a gene that expresses a viral coat protein, a gene that usually promotes viral replication, and a "glue" gene used to integrate viral DNA into the host genome.

These findings suggest that the transferred genes are embedded in a set of virus-like genes and a transposon, which together form a genetic factor that can be transmitted between different species. It is Maverick.

In addition, Maverick in one of the nematodes has an extra gene that expresses a protein called fusogen, which enables the virus to fuse with the cell and transfer its genome into the cell. Without fusin, the virus cannot transfer its genes. The existence of this protein strongly indicates that Maverick can produce virus-like particles and invade different types of cells.

Biologists quickly found many examples of other genes embedded in Maverick in the nematode genome. It is clear that what they found was not an isolated case of horizontal gene transfer. Among the more than 100 nematode genomes spanning more than 10 genera, two genes are often taken away by Maverick as "goods" and widely transmitted between different species. In gold deposits a kilometer deep from North America to India to South Africa, complete and incomplete genetic factors have infiltrated nematode populations in different parts of the world.

Although indirect evidence strongly suggests that Maverick promotes horizontal gene transfer between nematode species, biologists have not yet witnessed their actions. The next step for biologists is to find a way to see how Maverick produces virion-like particles under a microscope.

Reshaping our understanding of biological evolution Maverick is a class of ancient and fragmented genetic factors that are ubiquitous in the genomes of protozoa, fungi and animals (including humans). These large transferable genetic factors were initially thought to be ineffective, mutated remnants of outdated genes. But later studies have found that Maverick can be reactivated and they can facilitate horizontal gene transfer between some protozoan species. In multicellular organisms, intact and intact Maverick has never been studied in detail before. Therefore, nematodes provide a rare opportunity to study them.

This work has a potential practical application. Many nematode species are parasites that infect crops and livestock. If researchers understand how Maverick works, they may be able to use it to introduce specific disease-causing genes into parasites to prevent and control parasites.

In addition, Maverick can carry some genes with antiviral or antibacterial activity, which may be used to develop new drugs or vaccines. Maverick can also be used as a tool for gene transfer for applications such as gene therapy or gene editing.

The researchers also realized that horizontal gene transfer through Maverick and other genetic factors may be more widespread in nature than we thought. The horizontal transfer of some genes may affect the genetic diversity and adaptability of species, and even lead to the formation of new species or the extinction of some species. So, to really understand the evolution of organisms, we must also understand these "loners" who can move between species.

References:

Https://doi.org/10.1126/science.ade0705

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