Summary: Octopuses have an enormous repertoire of mRNA in their nervous tissues, reflecting an evolution similar to that of vertebrates. The results indicate that miRNAs play an important role in complex brain development.
Cephalopods such as octopuses, cuttlefish, and cuttlefish are highly intelligent animals with complex nervous systems. In Science Advances, a team led by Nikolaus Rajewski at the Max Delbrück Center has now shown that their evolution is related to the exponential expansion of the microRNA repertoire.
If we go back far enough in evolutionary history, we encounter the last known common ancestor of humans and cephalopods: a primitive worm-like animal with minimal intelligence and simple eye spots.
Later, the animal kingdom can be divided into two groups of organisms: those that have a backbone and those that do not.
While vertebrates, especially other primates and mammals, have evolved large, complex brains with diverse cognitive capabilities, invertebrates have not.
With one exception: cephalopods.
Scientists have long wondered why only these mollusks developed such a complex nervous system. Now an international team led by researchers from the Max Delbrück Center and Dartmouth College in the US has presented a possible cause.
In research published inScience is moving forwardThey explain that octopuses have an enormous repertoire of microRNAs (miRNAs) in their nervous tissues – mirroring similar developments that have occurred in vertebrates. This is what connects us to the octopus! A recent author of the paper, he explains that this finding likely means that micromolecules play an essential role in complex brain development.
In 2019, Rajewsky read a post about genetic analyzes on octopuses. Scientists have found that a lot of RNA modifications happen in these cephalopods – which means they make heavy use of certain enzymes that can recode their RNA.
“It got me thinking that not only are octopuses good at editing, but they also have other RNA tricks up their sleeves,” Rajewsky recalls. And so he began a collaboration with the marine research station Stazione Zoologica Anton Dohrn in Naples, which sent him samples of 18 different types of tissue from dead octopuses.
The results of these analyzes were surprising: “There was indeed a lot of RNA editing, but not in regions that we consider important,” says Rajewsky.
The most intriguing discovery was the massive expansion of a well-known group of RNA genes, the microRNA. A total of 42 new miRNA families were found – mainly in neural tissues and mostly in the brain.
Given that these genes were conserved throughout cephalopod evolution, the team concluded that they were clearly beneficial to the animals and therefore functionally important.
Rajowski has been researching microparticles for more than 20 years. Instead of being translated into messenger RNA, which provides the instructions for protein production in the cell, these genes code for small pieces of RNA that bind to messenger RNA and thus influence protein production.
These binding sites were also conserved throughout the evolution of cephalopods – another indication that these new micromolecules are of functional importance.
New microRNA families
“This is the third largest expansion of microRNA families into the animal world, and the largest outside of vertebrates,” said lead author Gregory Zolotarov, a Ukrainian scientist who trained in Ragowsky’s lab at MDC-BIMSB while pursuing his medical degree in Prague. , and later.
“To give you an idea of size, oysters, which are also mollusks, have only acquired five new microRNA families since the last ancestor they shared with octopuses — while octopuses have gained 90!” Oysters aren’t exactly known for their intelligence, Zolotaroff adds.
Rajewsky’s fascination with octopuses began 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 looked at each other for a few minutes – or so I thought.”
Looking at an octopus is very different from looking at a fish, he says: “It’s not very scientific, but their eyes radiate intelligence.” Octopuses have complex, human-like “camera” eyes.
From an evolutionary perspective, octopuses are unique among invertebrates. They have a central brain and a peripheral nervous system – an organ that can function independently. If the octopus loses its tentacles, the tentacle remains sensitive to touch and can move.
The reason why octopuses are so isolated in developing such complex brain functions may be that they use their arms very purposefully, for example as tools for opening shells.
Octopuses also show other signs of intelligence: they are very curious and can remember things. They can also get to know people and like one more than the other.
Researchers now believe they even dream by changing the color and texture of their skin while they sleep.
“They say if you want to meet a foreigner, you have to dive in and befriend an octopus,” says Rajewsky.
He now plans to join other octopus researchers to form a European network that will allow more exchanges between scientists. While the community is currently small, Rajewsky says interest in octopuses is growing worldwide, including among behavioral researchers.
It is fascinating, he says, to analyze a form of intelligence that has evolved completely independently of our own. But it’s not easy: “If you run tests with them with small snacks as a reward, they quickly lose interest. At least that’s what my colleagues tell me,” says Rajewski.
“Because octopuses are not typical model organisms, our biomolecular resources were very limited,” Zolotarov says. “So we don’t know exactly what types of cells express the new microRNA.” Rajewsky’s team now plans to apply a technique developed in Rajewsky’s lab that will make cells in octopus tissues visible at a molecular level.
About this genetics and evolutionary neuroscience news
author: John Schloter
Contact: Jana Schloter – MDC
picture: Image credits to Nir Friedman
Original search: open access.
MicroRNAs are closely associated with the emergence of the complex octopus brain reported by Nicholas Ragowski et al. Science is moving forward
MicroRNAs are intimately linked to the emergence of the complex octopus brain
Soft-bodied cephalopods, like octopuses, are exceptionally intelligent invertebrates with highly complex nervous systems that have evolved independently of vertebrates. Given the increased RNA editing in their neuronal tissues, we hypothesized that RNA regulation might play a key role in the cognitive success of this group.
For example, we characterized mRNA and small RNA in three cephalopod species, including 18 tissues from common octopus. We show that the major soft RNA innovation of cephalopods is an extension of the microRNA (miRNA) gene stock.
These evolutionarily novel miRNAs were primarily expressed in mature neural tissue and during development and retained at functional and therefore potentially functional target sites. In particular, the only similar expansions of miRNAs occurred in vertebrates.
Therefore, we propose that micromolecules are intimately linked to the development of complex animal brains.