A massive RNA editing in various species of cephalopods

California two-spot octopus (Octopus bimaculoides) (Photo Jeremy Selan)
California two-spot octopus (Octopus bimaculoides) (Photo Jeremy Selan)

An article published in the journal “Cell” describes a research on cephalopods that revealed that in particular in the coleoids (Coleoidea) subclass that includes octopuses, squid and cuttlefish there can be an RNA editing that allows a better adaptation to the environment and in particular to cold. According to the researchers this mechanism comes at the expense of the evolution of DNA.

Cephalopods are a class of marine mollusks and include some species highly evolved from the skills point of view such as the octopus. They can have characteristics so different from those of vertebrates that some scientists have likened them to aliens. In August 2015, the publication of an article in “Nature” that followed the DNA sequencing of the species Octopus bimaculoides led to various considerations about these characteristics but this new research shows that their DNA isnt’ the only thing different but also their RNA.

Generally, RNA is used to transcribe genetic instructions and for the synthesis of proteins and differs from the DNA for one of the four bases, which in RNA is uracil instead of thymine. Other than that, except for errors and some rare cases under 1% RNA is the copy of DNA or so it was thought but in cephalopods that’s not always true and especially in coleoids in even more than 60% of cases it can be modified.

The editing mechanism in coleoids uses enzymes that can change one of the RNA bases, adenine, into another bases called inosine. These enzymes are called ADAR (adenosine deaminases acting on RNA). It’s the most common mechanism among animals but it has these peaks among coleoids.

The peaks were detected in two species of octopus, in cuttlefish and in squid, all coleoids capable of complex social behavior and hunting. In other cephalopods belonging to other subclasses such as Nautilus pompilius and Aplysia californica this type of RNA editing reaches much lower levels. This means that it’s a characteristic typical of coleoids.

This extensive RNA editing capability comes at the expense of normal evolution. That’s because the ADAR enzymes require large structures called dsRNA composed of hundreds of nucleotides that are conserved in the genome of coleoids along with the editing sites. The consequence is that the mutation levels are significantly reduced.

The researchers plan to continue their research to explore the RNA editing mechanisms of coleoids and fully understand their consequences. This means for example understanding when these mechanisms are activated and what might be the environmental influences on them.

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