Cephalopods like octopuses, squids and cuttlefish are very smart animals with complex nervous systems. In “Science Advances”, a team led by Nikolaus Rajewsky 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 enough back in evolutionary history, we encounter the last known common ancestor of humans and cephalopods: a primitive wormlike animal with minimal intelligence and straightforward eyespots. Later, the animal kingdom may be divided into two groups of organisms – those with backbones and people without. While vertebrates, particularly primates and other mammals, went on to develop large and complicated brains with diverse cognitive abilities, invertebrates didn’t. With one exception: the cephalopods.

Scientists have long wondered why such a fancy nervous system was only capable of develop in these mollusks. Now, a global team led by researchers from the Max Delbrück Center and Dartmouth College in america has put forth a possible reason. In a paper published in “Science Advances”, they explain that octopuses possess a massively expanded repertoire of microRNAs (miRNAs) of their neural tissue – reflecting similar developments that occurred in vertebrates.

“So, that is what connects us to the octopus!” says Professor Nikolaus Rajewsky, Scientific Director of the Berlin Institute for Medical Systems Biology of the Max Delbrück Center (MDC-BIMSB), head of the Systems Biology of Gene Regulatory Elements Lab, and the paper’s last writer.

He explains that this finding probably means miRNAs play a fundamental role in the event of complex brains.

In 2019, Rajewsky read a publication about genetic analyses conducted on octopuses. Scientists had discovered that quite a lot of RNA editing occurs in these cephalopods – meaning they make extensive use of certain enzymes that may recode their RNA. “This got me considering that octopuses may not only be good at editing, but could produce other RNA tricks up their sleeve too,” 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 tissue types from dead octopuses.

The outcomes of this analyses were surprising: “There was indeed quite a lot of RNA editing happening, but not in areas that we imagine to be of interest,” says Rajewsky. Essentially the most interesting discovery was in truth the dramatic expansion of a widely known group of RNA genes, microRNAs. A complete of 42 novel miRNA families were found – specifically in neural tissue and mostly within the brain. Provided that these genes were conserved during cephalopod evolution, the team concludes they were clearly helpful to the animals and are due to this fact functionally essential.

Rajewsky has been researching miRNAs for greater than 20 years. As an alternative of being translated into messenger RNAs, which deliver the instructions for protein production within 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 – one other indication that these novel miRNAs are of functional importance.

Latest microRNA families

“That is the third-largest expansion of microRNA families within the animal world, and the biggest outside of vertebrates,” says lead writer Grygoriy Zolotarov, MD, a Ukrainian scientist who interned in Rajewsky’s lab at MDC-BIMSB while ending medical school in Prague, and later. “To offer you an idea of the size, oysters, that are also mollusks, have acquired just five latest microRNA families for the reason that last ancestors they shared with octopuses – while the octopuses have acquired 90!” Oysters, adds Zolotarov, aren’t exactly known for his or her intelligence.

Rajewsky’s fascination with octopuses began years ago, during a night visit to the Monterey Bay Aquarium in California. “I saw this creature sitting on the underside of the tank and we spent several minutes – so I believed – taking a look at one another.” He says that taking a look at an octopus may be very different to taking a look at a fish: “It is not very scientific, but their eyes do exude a way of intelligence.” Octopuses have similarly complex “camera” eyes to humans.

From an evolutionary perspective, octopuses are unique amongst invertebrates. They’ve each a central brain and a peripheral nervous system – one which is able to acting independently. If an octopus loses a tentacle, the tentacle stays sensitive to the touch and might still move. The rationale why octopuses are alone in having developed such complex brain functions could lie within the indisputable fact that they use their arms very purposefully – as tools to open shells, as an illustration. Octopuses also show other signs of intelligence: They’re very curious and might remember things. They also can recognize people and truly like some greater than others. Researchers now imagine that they even dream, since they modify their color and skin structures while sleeping.

Alien-like creatures

“They are saying if you desire to meet an alien, go diving and make friends with an octopus,” says Rajewsky. He’s now planning to affix forces with other octopus researchers to form a European network that can allow greater exchange between the scientists. Although the community is currently small, Rajewsky says that interest in octopuses is growing worldwide, including amongst behavioral researchers. He says it’s fascinating to investigate a type of intelligence that developed entirely independently of our own. However it’s demanding: “In the event you do tests with them using small snacks as rewards, they soon lose interest. A minimum of, that is what my colleagues tell me,” says Rajewsky.

“Since octopuses aren’t typical model organisms, our molecular-biological tools were very limited,” says Zolotarov. “So we do not yet know exactly which kinds of cell express the brand new microRNAs.” Rajewsky’s team at the moment are planning to use a method, developed in Rajewsky’s lab, which is able to make the cells in octopus tissue visible at a molecular level.

Source:

Max Delbrück Center for Molecular Medicine within the Helmholtz Association

Journal reference:

Zolotarov, G., et al. (2022) MicroRNAs are deeply linked to the emergence of the complex octopus brain. Science Advances. doi.org/10.1126/sciadv.add9938.