What do octopus and human brains have in common?

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Summary: Octopuses have a vastly expanded repertoire of miRNAs in their neural tissue, reflecting a similar evolution to that occurring in vertebrates. Findings suggest that miRNA plays an important role in complex brain development.

Source: MDC

Cephalopods like octopus, squid and cuttlefish are highly intelligent animals with complex nervous systems. In “Science Advances,” a team led by Nicholas Rajewski of the Max Delbrück Center has now shown that their evolution is linked to a dramatic expansion of their microRNA repertoire.

If we go far back in evolutionary history, we encounter the last known common ancestor of humans and cephalopods: a primitive insectoid with minimal intelligence and simple eyespots.

Next, 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 different cognitive abilities, invertebrates did not.

With one exception: cephalopods.

Scientists have long wondered why such a complex nervous system was able to develop only in these molluscs. Now, an international team led by researchers from the Max Delbrück Center and Dartmouth College in the US has pinpointed a possible reason.

In a paper published inScience advances“, they explain that octopuses contain a vastly expanded repertoire of microRNAs (miRNAs) in their neural tissue – reflecting a similar development to that occurring in vertebrates. “So, this is what connects us to octopuses!” Max Delbrück Center (MDC-BIMSB ), said Professor Nicholas Rajewski, Scientific Director of the Berlin Institute for Medical Systems Biology, Head of Systems Biology in the Gene Regulatory Elements Lab and last author of the paper. He explains that this finding likely means that miRNAs play a fundamental role in complex brain development.

In 2019, Rajewski read a publication about genetic analysis conducted on octopuses. Scientists have discovered that a lot of RNA editing occurs in these cephalopods – meaning they make extensive use of specific enzymes that can recode their RNA.

“It got me thinking that not only might octopuses be good at editing, but that they might have other RNA techniques up their sleeve,” Rajewski recalls. And so he began a collaboration with the Stazione Zoologica Anton Dohrn marine research station in Naples, which sent him 18 different types of tissue samples from dead octopuses.

The results of this analysis were surprising: “There was indeed a lot of RNA editing going on, but not in all the areas we believed to be of interest,” Rajewski said.

The most striking discovery was the dramatic expansion of microRNAs, a well-known group of RNA genes. A total of 42 novel miRNA families were found – particularly in neural tissue and mostly in the brain.

Given that these genes were conserved during cephalopod evolution, the team concluded that they were clearly beneficial to the animals and therefore functionally important.

Rajewski has been researching miRNAs for over 20 years. Instead of being translated into messenger RNA, which instructs the cell to produce proteins, these genes encode small pieces of RNA that bind to the messenger RNA and thus affect protein production.

These binding sites were also conserved throughout cephalopod evolution—another indication that these novel miRNAs are of functional importance.

New microRNA families

“This is the third largest expansion of the microRNA family in animals, and the largest outside of vertebrates,” said lead author Grigory Zolotarov, MD, a Ukrainian scientist who interned in Rajewski’s lab at MDC-BIMSB while finishing medical school in Prague, and later.

“To give you an idea of ​​the scale, oysters, which are also molluscs, have acquired only five new microRNA families from their last shared ancestor with octopuses—while octopuses have acquired 90!” Oysters, Zolotarov adds, aren’t exactly known for their intelligence.

Rajewski’s fascination with octopuses began a few years ago, during an evening visit to the Monterey Bay Aquarium in California. “I saw this animal sitting at the bottom of the tank and we spent a few minutes – so 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 their eyes convey a sense of intelligence.” Octopuses have similar complex “camera” eyes to humans.

From an evolutionary perspective, octopuses are unique among invertebrates. They have both a central brain and a peripheral nervous system – capable of functioning independently. If an octopus loses a tentacle, the tentacle remains sensitive to touch and can still move.

It shows a young octopus
Octopuses have complex “camera” eyes, as seen here in a juvenile creature. Credit: Nir Friedman

Why octopuses alone have developed such complex brain activity may be due to the fact that they use their arms very purposefully – for example, as tools to open shells.

Octopuses also show other signs of intelligence: they are very curious and can remember things. They get to know people and actually like some over others.

Researchers now believe that they even dream, since they change the color and texture of their skin while they sleep.

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It looks like a bowl of nuts

Alien-like creatures

“They say if you want to meet an alien, go diving and befriend an octopus,” Rajewski says.

He now plans to form a European network with other octopus researchers that will allow greater exchange between scientists. Although the community is currently small, Rajewski says interest in octopuses is growing worldwide, including among behavioral researchers.

He says it’s fascinating to analyze a form of intelligence that evolved completely independently of our own. But it’s not easy: “If you experiment with them using small treats as rewards, they soon lose interest. At least, that’s what my colleagues tell me,” says Rajewski.

“Since octopuses are not common model organisms, our molecular-biological tools were very limited,” says Zolotarov. “So we still don’t know exactly which cell type expresses the new microRNA.” Rajewski’s team now plans to apply a technique developed in Rajewski’s lab, which will visualize cells in octopus tissue at the molecular level.

This genetics and evolutionary neuroscience research report by Dr

Author: Jana Schluter
Source: MDC
Contact: Jana Schluter – MDC
Image: The film is credited to Nir Friedman

Original Research: Access to all.
MicroRNAs are deeply linked to the emergence of the complex octopus brain” by Nikolaus Rajewsky et al. Science advances


MicroRNAs are deeply linked to the emergence of the complex octopus brain

Soft-bodied cephalopods such as octopuses are exceptionally intelligent invertebrates with highly complex nervous systems that have evolved independently of vertebrates. Because of the enhanced RNA editing in their neural tissue, we hypothesized that RNA regulation may play a major role in the cognitive success of this group.

We thus profiled messenger RNAs and small RNAs in three cephalopod species comprising 18 tissues. Octopus vulgaris. We show that the major RNA innovation in soft-bodied cephalopods is microRNA (miRNA) gene amplification.

These evolutionarily novel miRNAs were initially expressed and conserved in adult neuronal tissues and during development and are thus likely functional target sites. The only comparable miRNA expansion occurred, significantly, in vertebrates.

Thus, we propose that miRNAs are closely related to the evolution of the complex animal brain.

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