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Evolution: were cancer genes originally passed on from plants to humans?


How does the transfer of genes between different species work?

Cancer affects many people around the world today. Cancer is widespread and causes millions of deaths. Experts are now trying to find out where the cancer genes in humans actually come from. The researchers found that a transfer of genes between plants and mammals radically changed the genes of mammals.

In their current study, the University of Adelaide scientists found that so-called cancer genes may have arisen from the transfer of genes between plants and mammals during evolution. These genes could be the source of why cancer develops in humans. The doctors published the results of their study in the English-language journal "Genome Biology".

Transfer of genes between animals and plants has taken place

In the world's largest study on so-called jumping genes, the researchers identified two specific jumping genes in over 759 plant, animal and fungal species. These bouncing genes are actually small pieces of DNA that can copy themselves through a genome and are known as transposable elements. The experts found that a transfer between plants and animals occurred during evolution.

Elements L1 and BovB were examined particularly closely

The scientists focused particularly on the elements L1 and BovB, which entered mammals as foreign DNA. This is the first time that researchers have been able to demonstrate that the L1 element, which is important for humans, has jumped between two species.

What is the horizontal transfer of genes?

Jumping genes copy themselves and insert themselves around genomes and into genomes of other species. How they do this is not yet known, although insects such as ticks or mosquitoes or possibly viruses could be involved. Nevertheless, the process remains a major mystery, explains study author Professor David Adelson from the University of Adelaide. This process is called horizontal transfer, which differs from normal parent-child transfer and has a huge impact on the evolution of mammals, the expert adds. For example, 25 percent of the genome of cows and sheep is derived from jumping genes.

Horizontal gene transfer is common

Think of jumping genes as a kind of parasite contained in DNA, the scientist says. This is not that serious, but worse is the fact that jumping genes get into other genomes and disrupt the genes there. Horizontal gene transfer is much more widespread than previously thought. Human L1 elements have been linked to cancer and neurological disorders. The researchers say that understanding the inheritance of this element is important for understanding the evolution of diseases.

Entry of L1 into the mammalian genome was a key factor

The researchers found that L1 occurs in plants and animals. L1 also occurs sporadically in fungi. The most surprising result, however, was the lack of L1 in two important mammal species, the Australian monotremes (platypus and echidna). This shows that the gene entered the evolutionary path of mammals after the deviation from monotremes. The entry of L1 into the mammalian genome was probably a key factor in the rapid evolution of mammals over the past 100 million years, study author Professor Adelson suspects.

These could be the carriers of BovB

So-called BovB elements were also examined. BovB is a much younger jumping gene. BovB has already been shown to jump between a bizarre range of animals including reptiles, elephants and marsupials. Ticks are probably the carriers in the cross-species BovB transfer. BovB has been transmitted between frogs and bats at least twice, the experts explain. New potential vectors are bed bugs, leeches and grasshoppers.

More research is needed

The team believes research into insect species will help to find more evidence of cross-species transfer. They also aim to study other jumping genes and to explore the possibility of aquatic vectors such as seaworms and nematodes. Although the most recent studies have included the analysis of genomes from over 750 species, the researchers believe that they have only just begun to scratch the surface of horizontal gene transfer. There is much more work to be done. (as)

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