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

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

Our glorious little blue marble of a planet is filled with an amazingly diverse array of life forms, but some are decidedly more peculiar than others.

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

If there’s one creature on Earth that’s strange enough to have evolved elsewhere, it’s the octopus, according to British neuroscientist Anil Seth. Some fringe theories even propose that octopuses may be aliens.

However, there is enough evidence to firmly link octopus evolution to Earth, and a team of scientists led by systems biologist Nikolaus Rajewsky at the Max-Delbrück-Center for Molecular Medicine has just found a new one.

And it’s a really intriguing one.

It’s a property that octopus brains actually share with human brains and the brains of other vertebrates: a huge repertoire of microRNA in their nervous tissue.

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

Octopuses are strange in many ways. They are also smart, like other cephalopods, such as squid. And squid brains have been found to be nearly as complex as canine brains. There is even evidence that octopuses can dream – rarely confirmed in invertebrates.

Unlike other intelligent animals, their nervous systems are highly distributed, with a significant portion of the roughly 500 million neurons scattered across their arms. Each arm is capable of making independent decisions and can continue to respond to stimuli even after being cut off.

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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 in invertebrates.

There is something else strange about octopuses and other cephalopods. Their bodies can quickly edit their RNA sequences to adapt to their environment. This is not how adaptation usually works; normally it starts with the DNA and those changes are passed on to the RNA.

This prompted Rajewsky to wonder what other RNA secrets octopuses might be hiding.

Analyzing 18 samples obtained from dead octopuses – provided by the marine research institute Stazione Zoologica Anton Dohrn in Italy – Rajewsky and his team determined RNA mainly from Octopus vulgaristhe common octopus. Also included in the study was a whole California octopus with two spots (Octopus bimaculoides) and a Hawaiian bobtail squid (Euprymna scolopes).

The sequencing provided a profile of the messenger RNAs and small RNAs therein. And the results were a surprise.

A common octopus (Octopus vulgaris). (Bernat Espigulé/iNaturalist, CC BY-NC 4.0)

“There was indeed a lot of RNA editing going on, but not in areas we think are of interest,” explains Rajewsky.

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

miRNA are non-coding RNA molecules heavily involved in regulating gene expression, binding to larger RNA molecules to help cells refine the proteins they make.

The fact that these miRNA families are preserved in the octopus, as are 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 carry the miRNAs with it. involved. of.

“This is the third largest expansion of microRNA families in the animal world, and the largest outside of vertebrates,” says biologist Grygoriy Zolotarov, now at the Center for Genomic Regulation in Spain, formerly of Rajewsky’s lab.

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

A two-headed octopus (Octopus bimaculoides). (wademcmillan/iNaturalist, CC BY-NC 4.0)

The only comparable expansions occurred in vertebrates, although the scale is a bit different. The human genome, for context, encodes approximately 2,600 mature miRNAs. But the number of octopus miRNA families is comparable to that of animals such as chickens and frogs.

The discovery, the researchers say, suggests that complex intelligence, including cephalopod smarts, may be related to this miRNA expansion.

Interestingly, this isn’t the only similarity between octopus and vertebrate brains. Scientists previously found that the brains of humans and octopuses both contain large numbers of a type of cell called transposons. It seems there’s a lot more going on inside an octopus’s head (and arms) than we understand.

The next step for Rajewsky’s team is to try to figure out exactly what those miRNAs do.

“The remarkable explosion of the miRNA gene repertoire in coleoid cephalopods may indicate,” the researchers write, “that miRNAs and perhaps their specialized neuronal functions are closely linked and may be required for the emergence of complex brains in animals.”

The research has been published in Scientific progress.

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