Horizontal gene transfer: new evidence studied (Introduction)

by David Turell , Tuesday, July 04, 2023, 01:32 (299 days ago) @ David Turell

The role of virus-like transposons:

https://www.sciencemagazinedigital.org/sciencemagazine/library/item/30_june_2023/411231...

"While studying the evolutionary origin of a selfish element in the nematode Caenorhabditis briggsae, we discovered that Mavericks, ancient virus-like transposons related to giant viruses and virophages, are one of the long-sought vectors of horizontal gene transfer. We found that Mavericks gained a novel herpesvirus-like fusogen in nematodes, leading to the widespread exchange of cargo genes between extremely divergent species, bypassing sexual and genetic barriers spanning hundreds of millions of years. Our results show how the union between viruses and transposons causes horizontal gene transfer and ultimately genetic incompatibilities in natural populations.

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"...transfer of genes between eukaryotes is thought to be rare, especially in metazoans, because it requires a chain of unlikely events: DNA must find its way out of the donor species, come in close contact with the germline of a second species, and finally integrate itself in the genome of the new host. Nonetheless, from antiparasitic toxins in butterflies to antifreeze proteins in fish, a growing body of evidence indicates that HGT between eukaryotes is far more common than was previously thought and could be an important evolutionary force.

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"Here, by studying the evolutionary origin of a selfish toxin-antidote (TA) element in the nematode Caenorhabditis briggsae, we found that Mavericks, ancient eukaryotic viruslike transposons, are widespread vectors of HGT between nematodes. Further, we showhowHGT fueled the evolution of genetic incompatibilities in natural populations.

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"Overall, our results indicate that two novel nematode protein families, WOSP proteases and KRMA kinases, are preferentially associated with Mavericks. These genes likely correspond to cargo sequences that were originally “captured” by Mavericks from nematode genomes during transposition and, as a result, broadly exchanged between species that have been reproductively isolated for tens or even hundreds of millions of years. In support of this view, we found that the GC content of wosp and krma genes largely matched that of host genes but differed significantly from that of Maverick core genes.

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"In this study, we provide evidence for widespread Maverick-mediated horizontal gene transfer across extremely divergent nematode species that drove the evolution of a novelMULE-associated selfish TA element. The TA found in C. briggsae is capable of both spreading in nature by poisoning individuals homozygous for the susceptible allele and changing its position in the genome through transposition.

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"We show in unprecedented detail how cooperation between parasitic genetic elements can lead to the evolution of new biological function and ultimately affect gene flow between populations. However, several intriguing aspects of the TA evolution are still unknown. For instance, it is not clear whether msft-1 became a toxin before or after its capture by the MULE transposon and if msft-1 has nonselfish roles that could also have contributed to the evolution of the TA.

"Our work reveals Mavericks as one of the long sought-after vectors of HGT. Because of their unique biology, which shares features of both transposons and viruses, Mavericks are responsible for the widespread transfer of genes across extremely divergent species...We hypothesize that Mavericks, like E. coli λ phage and human herpesvirus, integrate into the genome of their host and passively replicate until an environmental factor triggers the formation of infective particles (Fig. 6B). In support of this model, maviruses, virophages evolutionary related to Mavericks, are not constitutively expressed when integrated in protozoan genomes, but they are specifically transcribed after superinfection by the giant virus CrV."

Comment: wow!!! viruses and transposon-like viruses acting like bandits in the night, attacking genomes indiscriminately. A hidden mechanism for evolution?