What do the octopus and the human brain have in common

What do the octopus and the human brain have in common

Octopuses have compound “camera” eyes, as seen here on a juvenile animal. Credit: Nir Friedman

Cephalopods such as octopuses, squids and cuttlefish are highly intelligent animals with complex nervous systems. U Science Advancesa team led by Nikolaus Rajewsky from the Max Delbrück Center has now shown that their evolution is linked to a dramatic expansion of their microRNA repertoire.

If we go back far enough evolutionary history, we meet the last known common ancestor of humans and cephalopods: a primitive worm-like animal with minimal intelligence and simple eyespots. Later, the animal kingdom can be divided into two groups of organisms – those with backbones and those without. While vertebrates, especially primates and other mammals, developed large and complex brains with various cognitive abilities, invertebrates did not. With one exception: cephalopods.

Scientists have long wondered why such a complex nervous system could only develop in these molluscs. Now an international team led by researchers from the Max Delbrück Center and Dartmouth College in the United States has outlined a possible reason. In a paper published in Science Advancesthey explain it octopuses they have a massively expanded repertoire of microRNAs (miRNAs) in their composition neural tissue— reflecting a similar development that occurred in vertebrates.

“This is what connects us to the octopus,” says Professor Nikolaus Rajewsky, scientific director of the Berlin Institute for Medical Systems Biology at the Max Delbrück Center (MDC-BIMSB), head of the Laboratory for Systems Biology of Gene Regulatory Elements, and last author of the paper. He explains that this discovery likely means that miRNAs play a fundamental role in the development of complex brains.

In 2019, Rajewsky read a publication about genetic analyzes conducted on octopuses. Scientists have discovered that there is a lot of RNA editing going on in these cephalopods – meaning they make heavy use of certain enzymes that can recode their RNA.

“This got me thinking that not only are octopuses good at editing, they might have other RNA tricks up their sleeves,” says 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 tissue types from dead octopuses.

The results of the analyzes were surprising: “There was indeed a lot of RNA editing, but not in the areas we believe are of interest,” says Rajewsky. The most interesting discovery is actually the dramatic expansion of a well-known group of RNA genes, microRNAs.

A total of 42 new miRNA families were found – especially in nervous tissue and mainly in the brain. Given that these genes have been conserved throughout the evolution of cephalopods, the team concludes that they were clearly beneficial to animals and are therefore functionally important.

What do the octopus and the human brain have in common

Octopuses have both a central brain and a peripheral nervous system – one that is capable of acting independently. Credit: Nir Friedman

Rajewsky has been researching miRNAs for over 20 years. Instead of being translated into messenger RNAs, which provide instructions for protein production in the cell, these genes encode small pieces of RNA that bind to the messenger RNA and thus affect protein production. These binding sites were also conserved during cephalopod evolution—another indication that these novel miRNAs are of functional importance.

New families of microRNAs

“This is the third largest expansion of microRNA families in animal worldand the largest outside of vertebrates,” says lead author Grygoriy Zolotarov, MD, a Ukrainian scientist who interned in the Rajewsky lab at MDC-BIMSB while graduating from medical school in Prague, and later. , which are also molluscs, acquired only five new families of microRNAs from the last ancestors they shared with octopuses—while octopuses gained 90.”

Oysters, adds Zolotarov, are not really known for their intelligence.

Rajewsky’s fascination with octopuses began many years ago, during an evening visit to the Monterey Bay Aquarium in California. “I saw this creature sitting at the bottom of the tank and we spent a few minutes – I thought – looking at each other.” He says that watching an octopus is very different from watching a fish: “It’s not very scientific, but their eyes exude intelligence.” Octopuses have similar compound “camera” eyes to 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 alone in developing such complex brain functions could be the fact that they use their hands very purposefully – as tools for opening 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 are even dreaming, because they change the color and texture of their skin while they sleep.

What do the octopus and the human brain have in common

Cephalopods play with microRNAs (yellow): microRNAs may be linked to the emergence of complex brains in cephalopods. Credit: Grygoriy Zolotarov

Alien-like creatures

“They say if you want to meet an alien, go scuba diving and befriend an octopus,” says Rajewsky. He now plans to join forces with other octopus researchers to form a European network that will allow greater exchange between scientists. Although the community is currently small, Rajewsky says interest in octopuses is growing worldwide, including among behavioral researchers.

He says that it is fascinating to analyze a form of intelligence that developed completely independently of our own. But it’s not easy: “If you do tests with them using small snacks as a reward, they soon lose interest. At least, that’s what my colleagues tell me,” says Rajewsky.

“Since octopuses are not typical model organisms, our molecular biology tools were very limited,” says Zolotarov. “So we don’t yet know exactly which cell types express the new microRNAs.” Rajewsky’s team now plans to apply a technique, developed in Rajewsky’s lab, that will make cells in octopus tissue visible at the molecular level.

More information:
Grygoriy Zolotarov et al., MicroRNAs Are Deeply Linked to the Emergence of a Complex Octopus Brain, Science Advances (2022). DOI: 10.1126/sciadv.add9938.

Citation: What Octopus and Human Brains Have in Common (2022, November 25) Retrieved November 26, 2022, from

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