The probable key to the great intelligence of octopuses, squids and cuttlefish has finally been found, and it is a characteristic they have incredibly in common with humans: it is the vast repertoire, observed within the nervous tissue, of small RNA molecules , the single-stranded relative of DNA implicated in various biological roles of coding, decoding, regulation and expression of genes.
The discovery, published in the journal Science Advances and led by the German Max Delbrück Center, makes these molluscs a unique exception among invertebrate animals, which can remember information, recognize people and perhaps even dream.
While vertebrates, especially primates and other mammals, have evolved large and complex brains with diverse cognitive capacities, invertebrates have not.
With one exception: cephalopods, i.e. those marine molluscs which include octopuses, squids and cuttlefish.
Octopuses in particular, from an evolutionary point of view, represent a unique case: they have both a large central brain and a peripheral nervous system, which is able to act independently.
Researchers have long wondered why this strangeness and now the group led by Nikolaus Rajewsky may have found the answer: small RNA molecules known as microRNAs.
These structures particularly influence the production of proteins and in some cephalopods a great variety has evolved, almost as many as the hundreds produced by human DNA: "It is the third largest expansion of microRNA families in the animal world and the largest outside outside of vertebrates,” comments Rajewsky.
“To give an idea of the level of this expansion, other molluscs such as oysters have acquired only five new families of microRNAs since they separated from the common ancestor they shared with octopuses – adds the researcher – while the latter have evolved 90 new families”.