What's Common Between Human And Octopus Brains? Scientists Explore Reasons For Similarities

Special RNAs called miRNAs are found in the neural tissues of octopuses. This shows that developments that occurred in vertebrates also took place in octopuses. 

Octopuses are unique among invertebrates from an evolutionary point of view, one of the reasons being that both have a central brain and a peripheral nervous system. An octopus's peripheral nervous system can act independently. 

Did you know that octopus and human brains have certain things in common? Cephalopods such as octopuses, squids and cuttlefish have complex nervous systems, and are highly intelligent animals. A team of researchers led by Nikolaus Rajewsky at the Max Delbrück Center in Berlin, Germany, has shown that the evolution of cephalopods is linked to a dramatic expansion of their microRNA reserve. 

The last known common ancestor of humans and cephalopods in evolutionary history is a primitive worm-like animal with minimal intelligence and simple eyespots.

How vertebrates are more advanced than invertebrates

The animal kingdom can be divided into two groups of organisms, namely vertebrates and invertebrates. The vertebrates are the ones with a vertebral column or backbone, while invertebrates are the ones without a backbone. Vertebrates, which include primates and other mammals, evolved to develop large and complex brains with diverse cognitive abilities. 

Which invertebrates are an exception with respect to cognitive abilities?

Invertebrates, with the exception of cephalopods, did not develop diverse cognitive abilities. 

The team of researchers has presented a possible reason behind molluscs being the only invertebrates to develop a complex nervous system. The study describing the findings was recently published in the journal Science Advances. 

What are microRNAs?

The researchers have explained that octopuses have a massively expanded reserve of microRNAs or miRNAs, a class of non-coding RNAs that play important roles in regulating gene expression, and help cells control the kinds and amounts of proteins they make. These miRNAs are found in the neural tissues of octopuses. This shows that developments that occurred in vertebrates also took place in octopuses. 

In a statement released by Max Delbrück Center, Professor Nikolaus Rajewsky, the last author on the paper, said: "So, this is what connects us to the octopus!" 

Rajewsky also said that the finding probably means miRNAs play a fundamental role in the development of complex brains. 

According to Max Delbrück Center, Rajewsky read a publication about genetic analyses conducted on octopuses, in 2019. The publication stated that a lot of RNA editing occurs in cephalopods. This means that they make extensive use of certain enzymes that can recode their RNA. Rajewsky said this got him thinking that octopuses may not only be good at editing, but could have other RNA tricks up their sleeves too. Therefore, he began a collaboration with the Stazione Zoologica Anton Dohrn marine research station in Naples. The research station sent Rajewsky samples of 18 different tissue types from dead octopuses. 

42 novel microRNA families found in neural tissues of octopuses

Rajewsky said the results of the analysis were surprising because there was indeed a lot of RNA editing going on, but not in areas that researchers believe to be of interest. He added that the most interesting discovery was the dramatic expansion of a well-known group of RNA genes, microRNAs. The analyses found a total of 42 novel miRNA families, specifically in neural tissue and mostly in the brain. These genes were conserved during cephalopod evolution. Therefore, the researchers concluded that the genes were clearly beneficial to the animals and are functionally important.

microRNAs influence protein production

These genes, instead of being translated into messenger RNAs, encode small pieces of RNA that bind to messenger RNA and influence protein production. Messenger RNAs deliver the instructions for protein production in the cell. 

Octopuses have acquired a large number of new microRNA families

Grygoriy Zolotarov, the lead author on the paper, said this is the third-largest expansion of microRNA families in the animal world, and the largest outside of vertebrates. He added that oysters, which are also molluscs, have acquired just five new microRNA families since the last ancestors they shared with octopuses, while octopuses have acquired 90. He further said that oysters are not exactly known for their intelligence. 

The complex "camera" eyes of octopuses are similar to those of humans.

Why octopuses are unique among invertebrates

Octopuses are unique among invertebrates from an evolutionary point of view, one of the reasons being that both have a central brain and a peripheral nervous system. An octopus's peripheral nervous system can act independently. 

The statement said that if an octopus loses a tentacle, the tentacle remains sensitive to touch and can still move. Octopuses use their arms very purposefully, and this could be the reason why they are alone in having developed such complex brain functions. For instance, octopuses use their arms to open shells. 

Other signs of intelligence which octopuses show include being very curious and remembering things, recognising people, and liking some people more than others. Octopuses are believed to dream, and change their colour and skin structures while sleeping.

Zolotarov said it is not exactly known which types of cells express the new microRNAs. Therefore, the team now plans to apply a technique to make the cells in octopus tissue visible at a molecular level.