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Surprising New Findings: This Is What Actually Connects Us To Octopus

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Animals with sophisticated neurological systems, such as cephalopods like octopuses, squids, and cuttlefish, are extremely intelligent. In “Science Advances,” a team from the Max Delbrück Center led by Nikolaus Rajewsky has demonstrated that their development is linked to a huge increase in the number of microRNAs they have.

If we go far enough into the past of evolution, we’ll find the last common ancestor of humans and cephalopods: a basic, wormlike creature with limited intellect and rudimentary eyespots. In the end, the whole animal world may be roughly broken down into two categories: vertebrates and invertebrates.

Invertebrates, unlike their vertebrate counterparts, did not go on to develop massive, sophisticated brains capable of a wide range of cognitive capacities. This was notably true of primates and other mammals.

Except cephalopods.

For a very long time, researchers have pondered the question of why only these mollusks were able to build such a sophisticated neural system. Now, an international group spearheaded by scientists from the United States’ Max Delbrück Center and Dartmouth College has proposed an explanation. They describe how octopuses have a much increased repertoire of microRNAs (miRNAs) in their brain tissue, matching comparable advances that happened in vertebrates, in an article that was published in “Science Advances.” Professor Nikolaus Rajewsky, the paper’s final author and director of the Systems Biology of Gene Regulatory Elements Lab at the Berlin Institute for Medical Systems Biology (MDC-BIMSB), exclaimed, “So, this is what ties us to the octopus!” His research suggests that miRNAs play a crucial role in the formation of sophisticated brains, he says.

Rajewsky read a book in 2019 that described octopuses’ genetic analysis. Researchers had found evidence that these cephalopods engage in a significant amount of RNA editing, which indicates that they make considerable use of certain enzymes that are able to recode their RNA. This made Rajewsky wonder whether octopuses had further RNA tricks up their sleeves in addition to being skilled editors. So, he started working with the marine research station Stazione Zoologica Anton Dohrn in Naples. The station sent him samples of 18 different types of dead octopus tissue.

According to Rajewsky, the findings of this analysis were unexpected: “There was indeed a lot of RNA editing going on, but not in areas that we believe to be of interest.”  In fact, the most fascinating finding was the significant increase in the number of a well-known collection of RNA genes called microRNAs. Fourty-two new miRNA families were identified, almost entirely inside the brain and other neural tissues. The team thinks that these genes must have been functionally significant for cephalopods to have been conserved throughout their evolution.

Rajewsky has spent more than 20 years studying miRNAs. These genes encode short RNA fragments that bind to messenger RNA and regulate protein synthesis instead of being translated into messenger RNAs that carry the instructions for protein synthesis in the cell. These binding sites have also stayed the same during the evolution of cephalopods, which is another sign that these new miRNAs are important for function.

New families of microRNAs

“This is the third-largest expansion of microRNA families in the animal world, and the largest outside of vertebrates,” adds lead author Grygoriy Zolotarov. “To give you an idea of the scale, oysters, which are also mollusks, have acquired just five new microRNA families since the last ancestors they shared with octopuses – while the octopuses have acquired 90!” 

Zolotarov continues that oysters aren’t exactly renowned for their intellect.

Years ago, on a visit to the Monterey Bay Aquarium in California in the evening, Rajewsky developed a fascination with octopuses. 

“I saw this creature sitting on the bottom of the tank and we spent several minutes – so I thought – looking at each other.” 

The octopus, he says, is very different from the fish: “It’s not very scientific, but their eyes do exude a sense of intelligence.”

Octopuses have sophisticated “camera” eyes like humans.

Octopuses have sophisticated “camera” eyes like humans.

Octopuses stand apart from other invertebrates with regard to their distinct evolutionary history. They have a central neural system and a peripheral nervous system, the latter of which is capable of autonomous action. Even if an octopus loses one of its tentacles, the remaining tentacle is still mobile and touch-sensitive. The fact that octopuses utilize their arms extremely specifically, such as as tools to open shells, may be the reason why they are the only animal species to have evolved such complex brain functions. Octopuses exhibit additional intelligence in the form of curiosity and memory. They can also tell who people are, and some of them they like more than others. Researchers now think that they even dream because their skin and color change while they sleep.

Alien-like creatures

Rajewsky cites the saying, “They say if you want to meet an alien, go diving and make friends with an octopus.” 

Now, he wants to build a European network of octopus researchers to facilitate more communication and collaboration across their fields. Although there is not a large group of octopus researchers yet, Rajewsky claims that interest in octopuses is expanding across the globe. He finds it intriguing to study a sort of intellect that developed independently. But it’s challenging: “If you do tests with them using small snacks as rewards, they soon lose interest. At least, that’s what my colleagues tell me,” adds Rajewsky.

Octopuses have complex “camera” eyes, as seen here in a juvenile animal

Since octopuses aren’t typical model organisms, our molecular-biological tools were very limited,” says Zolotarov. “So we don’t yet know exactly which types of cell express the new microRNAs.”

Currently, Rajewsky’s team is preparing to use a method that was created in his lab to make the cells in octopus tissue visible at the molecular level.

Source: 10.1126/sciadv.add9938

Image Credit: Nir Friedman

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