Some modern people have stimulated the immune system thanks to a gene variant passed on by our old human family members, the Denisovans.
The variant – nowadays found in people with indigenous Australian, Melanesian, Maori or Polynesian origins – makes the wearer more resistant to certain diseases.
This is the first time that a single DNA sequence variant of an extinct human species has been shown to affect the activity of the modern human immune system.
The Denisovans were a kind of archaic man who lived from around 200,000 to 50,000 years ago.
Although only known from a few fossil specimens, genetic analysis has suggested that they once lived in a large area and were interwoven with our ancestors.
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Some modern people have stimulated the immune system thanks to a gene variant that the Denisovans of our species have been passed on by our old human family members. A microscope image of the small intestine of a mouse whose genome gave the researchers the Denisovan gene variant
The Denisovans were a kind of archaic man who lived from around 200,000 to 50,000 years ago. Although only known from a few fossil specimens, genetic analysis has suggested that they once lived in a large area and were interwoven with our ancestors
& # 39; Our study indicates that the Denisovan gene variant increases the inflammatory response in humans, & # 39; said lead researcher and immunologist Shane Gray of the Garvan Institute of Medical Research in Australia.
& # 39; Previous research has found collections of gene variants of extinct human species that appear to have benefited people who live at high altitudes or resist viruses. & # 39;
These, he explained, were & # 39; unable to determine which, if any, were actually functional & # 39 ;.
& # 39; This study is the first to identify a single, functional variant and suggests that it also had an evolutionary advantage over the human immune system. & # 39;
Little is known about the Denisovans, who lived in Asia and Southeast Asia between 200,000 and 50,000 years ago.
Their existence was only discovered in 2010 when a finger bone fragment was excavated in Denisova, the Siberian mountain cave for which they were named.
The finger, which belonged to a young girl, dates from around the end of the time of Denisovans, about 50,000 years ago.
Earlier this year, however, an analysis of a jaw bone on the Tibetan plateau showed that it had also been from a Denisovan.
This recent discovery suggested that these archaic people were more scattered than previously thought.
Experts believe that Denisovans crossed both Neanderthals and Homo sapiens when they migrated from Africa to modern-day Papua New Guinea and Australia.
Today, no less than five percent of the genome of indigenous Papua New Guinean origin comes from the Denisovans, genetic analysis has shown.
The variant – nowadays found in people with indigenous Australian, Melanesian, Maori or Polynesian origins – makes the wearer more resistant to certain diseases. Depicted a map with the frequency of the Denisovan gene variant in modern human populations
The findings were based on an analysis of the genomes of families from Sydney, Australia, where one child had a severe autoimmune or inflammatory condition.
These conditions include bowel disease, arthritis, multiple sclerosis, lupus, psoriasis and type 1 diabetes.
The researchers discovered that the family members with the gene variant – which experts called I207L – had increased immune responses and inflammatory responses.
Further research showed that I207L is not found in most populations – it is common in people with native Australian, Melanesian, Maori or Polynesian origins, and is also found in the genome of the Denisovan finger fossil.
& # 39; It was very exciting to make that connection, & # 39; said co-author and geneticist Owen Siggs of Flinders University in Australia, in Adelaide.
& # 39; The fact that this rare version of the gene was enriched in these populations and showed genetic traits of positive selection means that it was almost certainly beneficial to human health & # 39 ;, Professor Gray added.
Although the researchers found the variant in the Denisovan fossil, this was not present in the genomes of the Neanderthal remains found in the same cave.
This, the researchers said, indicates that the gene evolved in the Denisovan population sometime after deviating from the Neanderthals about 400,000 years ago.
It is believed that the Denisovans and our ancestors signed up about 50,000 years ago.
Finally, the researchers immediately began to investigate the effect of the I207L variant by replicating it within a mouse.
& # 39; When exposed to a pathogenic Coxsackie virus strain, mice with the Denisovan variant had stronger immune responses and resisted the infection better than mice without the Denisovan gene & # 39 ;, said the paper's author, Nathan Zammit.
This virus, he explains, was originally isolated from a fatal case of human infection.
The team discovered that the Denisovan gene variant – along with other similar ones – acts as a & # 39; temperature control button & # 39; for the immune system, which increases the level of response against various microbes.
The full findings of the study were published in the journal Nature Immunology.
WHO WERE THE DENISOVANS?
The Denisovans are an extinct species of people who seem to have lived in Siberia and even in Southeast Asia.
Although the remains of these mysterious early people have only been discovered in one location – the Denisova Cave in the Altai Mountains in Siberia, DNA analysis has shown that they were widespread.
DNA from these early people is found in the genomes of modern people in a large area of Asia, suggesting that they once covered a wide range.
DNA analysis of a snippet finger bone in 2010, (pictured) that belonged to a young girl, revealed that the Denisovans were a species that was related to, but different from, Neanderthals.
They are thought to be a sister species of the Neanderthals, who lived in West Asia and Europe around the same time.
The two species appear to have separated themselves from a common ancestor about 200,000 years ago, while they separated from the modern human Homo sapien lineage about 600,000 years ago.
Bone and ivory beads found in the Denisova cave were discovered in the same sediment layers as the Denisovan fossils, which led to suggestions that they had advanced tools and jewelry.
DNA analysis of a fragment of a five-digit finger bone in 2010, which belonged to a young girl, showed that it was a species that was related to, but different from, Neanderthals.
Later genetic studies suggested that the ancient human species separated from the Neanderthals somewhere between 470,000 and 190,000 years ago.
Since then, anthropologists have wondered whether the cave had been a temporary hiding place for a group of these Denisovans or whether it had formed a more permanent settlement.
DNA from molars from two other individuals, an adult male and a young female, showed that they died in the cave at least 65,000 years earlier.
Other tests have suggested that the young woman's tooth could be as old as 170,000 years.
It is thought that a third molar belonged to an adult man who died about 7,500 years before the girl whose little finger was discovered.
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