Octopus brains have evolved to share a surprising trait with our brains: ScienceAlert

EMBARGO Friday November 25 1900 GMT | Saturday 26 November 0600 AEST

Our gorgeous little blue marble of a planet is filled with an astonishingly diverse array of life forms, but some are certainly more exotic than others.

This is especially true of the octopus, an animal so bizarre that it regularly invites comparisons to aliens.

In fact, if there’s any creature on Earth strange enough to have evolved elsewhere, according to British neuroscientist Anil Seth, it’s the octopus. Some fringe theories even suggest that octopuses could be aliens.

However, there is plenty of evidence that strongly links octopus evolution to Earth, and a new team led by systems biologist Nicholas Ragowski of the Max Delbrück Center for Molecular Medicine has just found it.

Which is really interesting.

It’s a feature that octopus brains share with humans and other vertebrates: a huge repository of microRNA in their nervous tissue.

“This is what connects us to the octopus!” says Rajewsky.

Octopuses are curious in many ways. They are also intelligent, as are other cephalopods, such as cuttlefish. The brains of cuttlefish have been found to be as complex as the brains of dogs. There is even evidence to suggest that octopuses can dream – rarely confirmed in invertebrates.

Unlike other intelligent animals, its nervous system is highly distributed, with a large proportion of the 500 million odd neurons scattered throughout its arms. Each arm is able to make decisions independently and can even continue to respond to stimuli after being severed.

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The complex nervous system and intelligence of cephalopods was something of a puzzle. These traits are relatively common in vertebrates, but they really stand out among invertebrates.

There’s another really weird thing about octopuses and other cephalopods. Their bodies can quickly modify their RNA sequence on the fly to adapt to their environment. This is not how adaptation usually works; Normally, it starts with DNA, and these changes carry over into RNA.

This prompted Ragowski to wonder what other RNA secrets the octopuses might have.

Analyzing 18 samples obtained from dead octopuses — provided by the Stazione Zoologica Anton Dohrn Marine Research Institute in Italy — Rajewsky and his team sequenced RNA primarily from common octopusoctopus vulgaris. The study also included a whole California two-spotted octopus (octopus bimaculoides) and Hawaiian bobtail squid (Scolop Euprymna).

The sequencing provided a profile of the mRNA and the small RNAs within it. The results were surprising.

common octopus (common octopus). (Bernat Espegoli/i Naturalist, CC BY-NC 4.0)

“There has already been a lot of RNA editing going on, but not in areas that we think are important,” Rajewsky explains.

What the team found is that octopuses contain a lot of microRNA, or miRNA. They found 164 miRNA genes clustered in 138 miRNA families in the common octopus, and 162 miRNA genes clustered in the same 138 families in the California two-spotted octopus. And 42 of the families were new, mostly in brain and nervous tissue.

miRNAs are non-coding RNA molecules that are highly involved in the regulation of gene expression, and bind to larger RNA molecules to help cells adjust the proteins they produce.

The fact that these miRNA families are conserved in octopuses, as were the RNA-binding sites, suggests that they still play a role in octopus biology, although scientists don’t yet know what that role is, or which cells participate in the RNA. . with.

“This is the third largest expansion of microRNA families in the animal world, and the largest outside of vertebrates,” says biologist Grigory Zolotarov, who is now at the Center for Genome Organization in Spain, formerly of Ragoski’s lab.

“To give you an idea of ​​size, oysters, which are also mollusks, have only acquired five new microRNA families since they last shared the ancestor they shared with octopuses — while octopuses have gained 90!”

two-pointed octopus (octopus bimaculoides). (@wademcmillan/iNaturalist, CC BY-NC 4.0)

The only similar enlargements have occurred in vertebrates, although at a slightly different scale. The human genome encodes, for context, about 2,600 mature miRNAs. But there are as many miRNAs in the octopus family as there are animals like chickens and frogs.

The researchers say the discovery suggests that complex intelligence, including that of cephalopods, may be linked to the expansion of RNA.

Interestingly, this is not the only similarity between octopus brains and vertebrate brains. Scientists previously found that human and octopus brains contain a large number of a type of cell called transposons. There seems to be a lot more going on in an octopus’ head (and its arms) than we understand.

The next step for Rajewsky’s team is to try to figure out exactly what these microscopic particles are doing.

The researchers write, “The observed explosion in the repertoire of miRNA genes in coliform cephalopods may indicate that micromolecules and perhaps their specialized neural functions are closely related and may be required for the emergence of complex brains in animals.”

Research published in Science advances.

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