Species Mixing Made Easy: the Role of Virus-like Transposons

“Scientists have identified a vector of horizontal gene transfer (HGT) in worms, which could lead to the discovery of further vectors of HGT in eukaryotes. HGT is a major evolutionary force within microbial communities and allows for the acquisition of novel traits that are unique…”

Fish living in the Arctic and Antarctic oceans have evolved 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, over a decade ago, scientists were astounded to discover that herrings and smelts – two completely different species – have the exact same antifreeze protein encoded in their genomes, indicating a gene transfer between them. This rare phenomenon, known as horizontal gene transfer (HGT), has puzzled evolutionary biologists for a long time.

Scientists have discovered new instances of HGT across all branches of life over the years, but the mechanisms responsible for these transfers have largely remained unknown. Recently, Burga’s group at IMBA caught an HGT event in the animal kingdom red-handed and identified one of its long-sought vectors. By means of genetic detective work, Burga and his team showed an event of HGT between two reproductively isolated worm species that are genetically as different from each other as humans are from fish. More importantly, they could identify what caused it: a family of virus-like transposons called Mavericks.

The scientists argue that the union between transposons and viruses is a key factor in mediating HGT. Mavericks contained genes encoding viral elements, such as a capsid and a DNA polymerase, which are not enough to allow a transposon to jump from its host’s genome and infect the cells of a completely different host. However, the IMBA researchers found the missing link: Mavericks in worm genomes have acquired a so-called fusogen protein, a transmembrane protein that mediates membrane fusion between different cells.

By acquiring a fusogen, the authors hypothesize that worm Mavericks became capable of forming virus-like particles that can fuse with another organism’s cell membranes and infect them. “Transposons and viruses can be thought of as nature’s melting pot. Their union can have unpredictable repercussions and lead to genomic innovation,” says Burga.

This discovery is fascinating because it sheds light on how genes can “jump” between completely different species, and it highlights the importance of transposons and viruses in mediating HGT. It also has agricultural and medical relevance, as the union between transposons and viruses can lead to genomic innovation and the evolution of genetic incompatibilities.

Sonya A. Widen, Israel Campo Bes, Alevtina Koreshova, Pinelopi Pliota, Daniel Krogull, Alejandro Burga. Virus-like transposons cross the species barrier and drive the evolution of genetic incompatibilities. Science, 2023; 380 (6652) DOI: 10.1126/science.ade0705