Octopus Brains Evolved to Share a Surprising Trait in With Our Brains - ScienceAlert

It's a trait that octopus brains actually share with human brains, and the brains of other vertebrates: a huge repertoire of microRNA in their neural tissue.

Analyzing 18 samples obtained from dead octopuses – supplied by the Stazione Zoologica Anton Dohrn marine research institute in Italy – Rajewsky and his team sequenced RNA mainly from from Octopus vulgaris, the common octopus.

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.

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

"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 Centre for Genomic Regulation in Spain, formerly of Rajewsky's lab.

"To give you an idea of the scale, oysters, which are also mollusks, have acquired just five new microRNA families since the last ancestors they shared with octopuses – while the octopuses have acquired 90!".

"The notable explosion of the miRNA gene repertoire in coleoid cephalopods may indicate," the researchers write, "that miRNAs and, perhaps, their specialized neuronal functions are deeply linked and possibly required for the emergence of complex brains in animals."