The question we ask ourselves each summer is an empty one: Why is it so difficult, even impossible, to escape the sight of ruthless mosquitoes? . Why do they bite me more than anyone else? Scientists and repellent makers believe that carbon dioxide (CO₂), which we exhale when we breathe, and octanol, a volatile compound found in sweat, are the main victims of mosquitoes. I knew long ago that it would form an aerial highway that I would use to lead to. What scientists didn’t know, but they’ve now discovered, is that mosquitoes, unlike other creatures in the animal kingdom, have multiple odor and taste receptors on each of their thousands of olfactory neurons. .

In 2004, researchers Richard Axel and Linda Bach were awarded the Nobel Prize in Medicine for their discovery of “olfactory receptors and the organization of the olfactory system.” A decade ago, Axel and Buck found that there are about 1,000 genes involved in the olfactory process, and that they are involved in an equal number of olfactory receptors. We showed that only one of these receptors was expressed (a phenomenon called the “one neuron, one receptor” rule) and that this information was sent as an electrical signal to the olfactory bulb. The mammalian brain that processes and interprets scents. But according to Leslie Vosshall, director of the Neurogenetics and Behavioral Laboratory at Rockefeller University in New York and a former postdoctoral fellow in Axel’s lab, “All of Buck and Axel’s rules were trashed by mosquitoes.” got thrown away.

Vosshall directs a research program aimed at understanding the olfactory system of mosquitoes.Specifically, her work focuses on mosquito seeds Aedes aegyptiIt is commonly known as the “dengue mosquito” because of its role in spreading the virus that causes dengue fever.However Aedes aegypti In addition to transmitting dengue fever, it can also transmit the pathogens that cause yellow fever, chikungunya, Zika and Mayaro virus disease.Figure out how to block odorant receptors Aedes aegypti Women who bite can have a significant impact on global health and disease prevention.

Latest research by Vosshall and her colleagues published in scientific journal cellshowing that mosquitoes, like all other animals, have a few neurons with only a single olfactory receptor. AE.Aedes aegypti Mosquitoes have many neurons that co-express multiple receptor genes. “If you’re a human and you lose a single odorant receptor, all neurons that express that receptor lose the ability to smell that odor,” Vosshall says. “We need to do more to destroy mosquitoes because removing a single receptor is ineffective. We have to take into consideration how indestructible it is for us.”

Once the mosquito genome was sequenced and the genes expressing the olfactory receptors identified, researchers used a variety of techniques to track the genes and localize them within individual neurons. Using a modern gene-editing technique known as CRISPR, they were able to introduce fluorescent proteins of different colors corresponding to different receptors. We found that many neurons have multiple active receptors. Vosshall’s team found that neurons stimulated by the human odor octenol were also activated by other ammonia-derived chemicals, or amines, that similarly function to attract mosquitoes.

“Surprisingly, the neurons that detect humans via 1-octen-3-ol and amine receptors were not separate populations,” said a Boston University researcher and co-author of the study. explains Meg Younger, who is In an email to EL PAÍS, Rockefeller University researcher Margo Herre, lead author of the study, added: [volatile chemical compounds] Further research is needed to determine the exact composition of human odors and which of these odors mosquitoes can detect. ”

The overall picture drawn by these findings is AE.Aedes aegypti It has a double or triple redundancy system. That is, if it fails to recognize one scent, it will move on to detect a second or third scent. And when we detect all of them, the signal is amplified. Vosshall explains:

This discovery could have far-reaching implications.On the one hand, it may help explain why attempts to control mosquitoes and limit their role in the spread of pathogens have been more or less unsuccessful. AE.Aedes aegypti They are blood-sucking (hematosuckers) “because they need the proteins present in the blood to mature their eggs.” A mosquito’s ability to bite avidly is the product of millions of years of evolution.

So far, attempts to block mosquito olfactory receptors by genetic engineering have failed. Probably because it started with the generally accepted idea (disproved by new findings) that a particular gene expresses only one receptor of her for each type of neuron. This also explains the relative but not complete effectiveness of DEET, a repellent discovered by the US military in 1946 and still the main active ingredient in most chemical insect repellents. Although the mechanism is not yet fully understood, it is believed that N,N-diethyl-meta-toluamide (DEET) inhibits CO₂ or lactate receptors, but not other odorants in the same neurons. known to have receptors. The good news is that researchers understand that they need to focus their efforts on multiple receptors at once, not just one.

Whether this new finding applies to other species of mosquitoes remains to be seen – Aedes albopictusfor example; other species of Anopheles mosquito, a genus of malaria-carrying mosquitoes. Or, except in rare cases, Culex pipiens mosquitoes, such as common mosquitoes and tiger mosquitoes, tend to cause more than discomfort and itching. Potter fears that will happen. In 2019, his lab opened Drosophila (Drosophila melanogaster) also have double or triple expression of the receptor in single neurons, and this spring they published findings showing the same expression in species. Anopheles mosquito mosquito.

“This redundancy may be common among insects,” says Potter, who was not involved in the study. Reflecting on the new findings, Potter explains: As far as we know, that was the rule. ” However, he said: Vosshall’s work suggests that mosquito olfactory neurons may be much more adaptive, especially to the primary odors that need to be detected to localize the host. ”