The parasite “steals” its host's genes to better control it

In the living world, parasites do not lack imagination to ensure their survival. Many of them go so far as to control the behavior of their host to carry out their reproductive cycle. This is the case of nematodes, which are unsegmented worms with a cylindrical body, very long (10 to 70 cm) and thin (0.5 to 5.5 mm), and whose filamentous appearance is reminiscent of noodles. They are born in aquatic environments – freshwater, saltwater and wetland – and then use aquatic insects such as mayflies to reach land, where they wait to be devoured by locusts or praying mantises. Since then, it develops inside its new host, controlling its behavior, and causing it to jump into the water, where it completes its life cycle by reproducing. But how is such misappropriation of life possible? Previous studies have revealed that nematomorphs control their host's biological pathways to direct them toward a light source, which generally leads them closer to a water source. To do this, parasites likely use proteins that mimic those found in the host's central nervous system. However, Takuya Sato, of Kobe University in Japan, and colleagues have just shown that a surprising mechanism of gene transfer would be involved in the acquisition of this ability to mimic by parasites.

In this study, the researchers were interested in nematodes of this genus ropes, That infects the praying mantis (religious mantis). They analyzed the expression of their genes before, during and after the phase during which they manipulated their host, and thus found more than 3,000 genes whose expression level increased during the manipulation process, in addition to 1,500 genes whose activity was decreasing. On the other hand, analysis of the expression of genes involved in the functioning of the brain of the affected mantis showed no change compared to what was observed in the healthy mantis. This observation therefore suggests that the nematomorph itself produces proteins used to control the behavior of its host.

Takuya Sato and his colleagues then compared the genes whose expression was increased with those in the praying mantis; About 1400 they look similar. On the other hand, the team looked for these same genes in other samples of nematodes that infect different hosts, such as locusts. The result: Of the 1,400 genes involved, most were dramatically different, or absent. These observations support the hypothesis of horizontal gene transfer – the process by which genes are transferred from one organism to another without resorting to reproduction. This mechanism, discovered by Japanese researchers in 1959, has major evolutionary implications; It allows organisms to acquire new genes and therefore new functions quickly, helping them adapt to new environments and lifestyles. Nematomorph genes – associated with neuromodulation, phototaxis and management of the organism's internal clock – thus result from multiple gene transfers between praying mantises and their parasites during the latter's development.

Horizontal gene transfer is one of the main ways in which bacteria develop resistance to antibiotics. This is a well-known phenomenon among unicellular organisms, but until recently was thought to be less common among multicellular organisms. A future case study of these conversions will allow us to better understand this phenomenon as an evolving tool in general.