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Could humans ever develop venom? People are very unlikely to join rattlesnakes and platypus among poisonous animals, but new research reveals that humans have the toolkit for producing venom – in fact, all reptiles and mammals have it.
This collection of flexible genes, particularly associated with the salivary glands in humans, explains how venom evolved independently from non-venomous ancestors more than 100 times in the animal kingdom.
“Essentially, we have all the building blocks in place,” said study co-author Agneesh Barua, a doctoral student in evolutionary genetics at the Okinawa Institute of Science and Technology in Japan. “Now it’s up to evolution to take us there. “
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Oral venom is common throughout the animal kingdom, present in creatures as diverse as the spiders, snakes and slow lorises, the only known venomous species of primate. Biologists knew that oral venom glands are altered salivary glands, but new research reveals the molecular mechanics behind the change.
“This will be a real milestone in the field,” said Bryan Fry, biochemist and venom expert at the University of Queensland in Australia who was not involved in the research. “They did an absolutely stunning job of some extremely complex studies.”
A flexible weapon
Venom is the ultimate example of nature’s flexibility. Many toxins present in the venom are common to very different animals; some components of Centipede the venom, for example, is also found in snake venom, said Ronald Jenner, a venom researcher at the Natural History Museum in London who was not involved in the research.
The new study doesn’t focus on the toxins themselves, as these evolve quickly and are a complex mix of compounds, Barua told Live Science. Instead, Barua and study co-author Alexander Mikheyev, an evolutionary biologist at Australian National University who focuses on “household” genes, genes that are associated with venom but are not responsible for it. of the creation of the toxins themselves. These regulatory genes form the basis of the entire venom system.
Researchers started with the Taiwan habu genome (Trimeresurus mucrosquamatus), a well-studied brown viper, in part because it is an invasive species in Okinawa.
“Since we know the function of all the genes that were present in the animal, we could just see which genes the genes in the venom are associated with,” Barua said.
The team discovered a constellation of genes common in several body tissues of all amniotes. (Amniotes are animals that fertilize their eggs internally or lay eggs on land; they include reptiles, birds, and some mammals.) Many of these genes are involved in protein folding, Barua said, which makes sense, because poisonous animals have to make a lot of it. toxins, which are made from protein.
“A tissue like this really has to make sure that the protein it produces is of high quality,” he said.
Not surprisingly, the same types of domestic regulatory genes are found in abundance in the human salivary gland, which also produces a significant stew of protein – found in saliva – in large quantities. This genetic basis is what enables the wide array of independently evolved venoms across the animal kingdom.
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From non-poisonous to poisonous
In other words, every mammal or reptile has the genetic scaffolding on which an oral venom system is built. And humans (with mouse) also already produce a key protein used in many venom systems. Kallikreins, which are proteins that digest other proteins, are secreted in saliva; they are also a key component of many venoms. That’s because kallikreins are very stable proteins, Fry said, and they don’t just stop working when subjected to a mutation. Thus, it is easy to obtain beneficial mutations of kallikreins which make the venom more painful and deadly (one effect of kallikreins is a sharp drop in blood pressure).
“It is no coincidence that kallikrein is the type of component most widely secreted in venoms throughout the animal kingdom, because in whatever form it is a very active enzyme and it will start to do so. messed up stuff, ”Fry said.
Kallikreins are therefore a natural starting point for theoretically poisonous humans.
If after the 2020 drama, Barua joked, “people have to be poisonous to survive, we could potentially start to see increasing doses of kallikreins.”
But that’s not so likely – not unless humans’ currently successful strategies for acquiring food and choosing mates start to crumble, anyway. The venom most often evolves as a method of defense or as a means of subduing prey, Jenner told Live Science. The type of venom that evolves largely depends on how the animal lives.
Evolution can essentially adapt venom to an animal’s needs through natural selection, Fry said. There are desert snakes, for example, which have a different venom although they are of the same species, just because of where they live, he said: on the desert floor, where snakes mainly hunt mice, the venom acts mainly on the circulatory system, as it is not difficult for a snake to follow a dying mouse a short distance on level ground. In the nearby rocky mountains, where snakes mainly hunt lizards, venom is a potent neurotoxin, because if the prey is not immediately immobilized, it can easily squeeze into a crevice and disappear for good.
Some mammals have venom. Vampire bats, which have poisonous saliva that prevents blood clots from forming, use their chemical weapon to feed on wounds more efficiently. Poisonous shrews and shrew-like solenodons (small burrowing mammals) can exceed their weight class by using their venom to subdue prey larger than they could otherwise kill. Shrews also sometimes use their venom to paralyze their prey (usually insects and other invertebrates) to store them and nibble on them later. Meanwhile, platypuses, which don’t have a poisonous bite but have a poisonous spur on their hind legs, primarily use their venom in fights with other platypuses on mates or territory, Jenner said.
Humans, of course, have invented tools, weapons, and social structures that do most of this work without the need for poisonous fangs. And the venom is expensive, too, Fry said. Building and folding all of these proteins requires energy. For this reason, the venom is easily lost when not in use. There are species of sea snakes, Fry said, that have residual venom glands but are no longer poisonous as they have gone from feeding on fish to feeding on fish eggs, which do not require toxic sting.
The new research may not raise much hope for new superpowers for humans, but understanding the genetics behind venom control could be essential for medicine, Fry added. If a snakes the brain had to start expressing the genes that its poison glands expressed, the snake would immediately die of self-toxicity. Learning how genes control expression in different tissues could be helpful in understanding diseases such as cancer, which causes illness and death largely because the tissues start to grow uncontrollably and secrete products in them. places on the body where they shouldn’t.
“The importance of this document goes beyond this area of study, as it provides a starting platform for all of these types of interesting questions,” said Fry.
The research was published online Monday, March 29 in the journal Proceedings of the National Academy of Sciences.
Originally published on Live Science.
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