The complexity of octopus nervous system has intrigued the scientific community for many years. In general, to the rest of the humans, too we are surprised that these cephalopod mollusks (apparently simple organisms) display behaviors and abilities that humans qualify as signs of intelligence.
Various science fiction authors and even some scientists between daring and provocative They have suggested that octopuses could be extraterrestrial beings or, at least, the fruit of a type of life that arrived -already formed- from outer space. At the moment, as far as we know, there is no evidence that octopods are aliens.
A team led by Nikolaus Rajewsky, a researcher at the Max Delbrück Center for Molecular Medicine in Berlin (Germany), in collaboration with experts from Dartmouth College in the United States, now proposes a more terrestrial explanation for the complexity of the nervous system of octopuses and others. cephalopods. The emergence of intelligence in this order of molluscs could be motivated by the massive expansion of their microRNA (miRNA) repertoire in their nervous tissue, reflecting similar developments that occurred in vertebrates, Rajewsky’s team proposes.
The results of this research have been published in the journal Science Advances (version on line November 25).
radically different from humans
If we go back far enough in evolutionary history, we find ourselves with the last known common ancestor of humans and cephalopods: a primitive, worm-like animal with minimal intelligence and simple eyespots.
Subsequently, the animal kingdom can be divided into two groups of organisms: those with backbones and those without. While vertebrates, particularly primates and other mammals, evolved large, complex brains with diverse cognitive abilities, invertebrates did not. With one exception: cephalopods, recalls the Max Delbrück Center in an informative note.
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Nikolaus Rajewsky, scientific director of the Institute for Medical Systems Biology of the Max Delbrück Center and head of the Gene Regulatory Element Systems Biology Laboratory, believes that with the data provided in his study it can be concluded that the link shared by octopuses ( and other cephalopods) and humans (and other vertebrates) are precisely the great variety of miRNAs in nervous tissue.
Basis of scientific study
In 2019, Rajewsky read a post about genetic analyzes done on octopuses. The scientists had discovered that a great deal of RNA editing occurs in these cephalopods, which means they make extensive use of certain enzymes that can recode their RNA. “This got me thinking that octopuses may not only be good at editing, but they might also have other RNA tricks up their sleeves,” recalls Rajewsky. And so he began a collaboration with the Stazione Zoologica Anton Dohrn marine research station in Naples, which sent him samples of 18 different types of tissue from dead octopuses.
The results of these analyzes were surprising: “Indeed, a lot of RNA editing was being done, but not in areas that we think are of interest,” says Rajewsky. The most exciting discovery was, in fact, the spectacular expansion of a well-known group of RNA genes, the microRNAs. A total of 42 new miRNA families were found, specifically in neural tissue and mainly in the brain. Since these genes were conserved during cephalopod evolution, the team concludes that they were clearly beneficial to the animals and therefore functionally important.
The scientific study of cephalopod intelligence is still in its early stages.
Rajewsky has been researching miRNAs for more than 20 years. Instead of being translated into messenger RNAs, which deliver the instructions for protein production in the cell, these genes encode small pieces of RNA that bind to messenger RNA and thus influence protein production. These binding sites were also conserved throughout cephalopod evolution, another indication that these new miRNAs are of functional importance.
New RNA families
“This is the third largest expansion of microRNA families in the animal world and the largest outside of vertebrates,” says lead author Grygoriy Zolotarov, MD, a Ukrainian scientist who interned in Rajewsky’s lab at MDC- BIMSB while finishing medical school in Prague. , and then. “To give you an idea of the scale, oysters, which are also molluscs, have acquired just five new microRNA families since their last shared ancestors with octopuses, while octopuses have acquired 90!” Oysters, Zolotarov adds, aren’t exactly known for their intelligence.
Rajewsky’s fascination with octopuses began years ago, during a nocturnal visit to the Monterey Bay Aquarium in California. “I saw this creature sitting at the bottom of the tank and we spent several minutes, I thought, looking at each other.” He says that looking at an octopus is very different from looking at a fish: “It’s not very scientific, but its eyes exude a sense of intelligence.” Octopuses have equally complex “camera” eyes for humans.
From an evolutionary perspective, octopuses are unique among invertebrates. They have both a central brain and a peripheral nervous system, one that is capable of acting independently. If an octopus loses a tentacle, the tentacle remains sensitive to touch and can still move.
The reason why octopuses are the only ones to have developed such complex brain functions could lie in the fact that they use their arms very purposefully, as tools to open shells, for example. Octopuses also show other signs of intelligence: they are very curious and can remember things. They can also recognize people and actually like some more than others. Researchers now believe that they even dream, as the color and structures of their skin change while they sleep.
Rajewsky has proposed joining forces with other octopus researchers to form a European network that will allow for greater exchange of specific knowledge. Although the community is currently small, Rajewsky says interest in octopuses is growing around the world, including among behavioral researchers. “It is fascinating to analyze a form of intelligence that developed completely independently of ours,” says this researcher.
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little genetic pieces
Micro-RNAs (miRs) are small non-coding RNA molecules (between 19 and 25 nucleotides) that regulate gene expression at the post-transcriptional level. They generally act on gene expression through the silencing or degradation of messenger RNA (mRNA), and are involved in the regulation of various biological processes, such as cell differentiation, proliferation, apoptosis, and embryonic and tissue development. In animals, microRNAs are found encoded in individual genes (coding for a single microRNA), grouped in clusters (groups of genes that code for several different microRNAs) or in introns of protein-coding genes.