The naturalist Sy Montgomery once wrote that “no sci-fi alien is so startlingly strange” as an octopus. Aside from their obvious extraterrestrial-like characteristics – writhing tentacles, squishy bodies, bulging eyes and the ability to change colour – octopuses have a hidden “otherworldly” feature. Along with other cephalopods such as squids and cuttlefish, they can edit and direct their own genes.
Generally, an evolutionary change occurs when DNA undergoes a mutation due to various environmental factors. The mutation in DNA is then transcribed into RNA – a cousin of DNA that transfers instructions from genes to cells that produce proteins. Given the prior mutation, an altered protein is formed, which translates to an altered trait. In short, DNA – protein – trait.
Not so for our eight-armed underwater friends, however. Or is it six arms and two legs?
A recent study published in the scientific journal Cell suggests that for octopuses and other cephalopods, proteins can be altered without the prior mutation of DNA. This is referred to by the researchers as RNA editing.
To be honest, the science went over my head, so I contacted the lead author of the study, Noa Liscovitch-Brauer, to break it down.
In layman’s terms, what is RNA editing?
RNA editing is a cellular mechanism in which an Adenosine in an RNA molecule gets modified and changed into another nucleotide, an Inosine. If this happens in a messenger RNA that codes for a protein, this can translate into a change in the protein structure – this is a way to create changes in proteins and recode them, using the RNA and not the DNA.
Still quite hard to understand… Does this mean that cephalopods have evolved differently from us?
Using RNA editing to recode proteins happens in all other animals as well, but this is a very rare thing and seems to be generally non-adaptive. In cephalopods, on the other hand, this is the rule and not the exception – most of the proteins in cephalopod brains get recoded using this mechanism. It seems as if cephalopods have developed a different way to create diversity in their proteins than any other animal.
Why is it that RNA is so widespread in cephalopods? Does it have to do with a short life span, among others?
We don’t know yet exactly how they use editing. We have looked at some specific examples and seen that editing causes a change in electrophysiological properties of ion channels – so they can use it to alter neural activity. We have wondered about the connection to their short life span – one hypothesis is that the massive recoding causes many proteins to fold incorrectly and the price they pay is in a shorter life span. But this is just a hypothesis at this point.
Does it provide answers to their high intelligence?
We can’t say that for sure, but that would be my guess. What’s interesting is that we do see this happen only in family members who display complex and unusual behaviours, while in a more ancient, simply behaving cephalopod, we do not see protein recoding.
Does RNA editing indicate that octopuses are genetically similar to their ancestors (since it isn’t their DNA that changes)?
Since we see the editing in one group of cephalopods – coleoid cephalopods [octopus, squid and cuttlefish] – but not in the more ancient nautiloids, we actually conclude that this is probably their own invention, and we think it might go together with the sophisticated behaviours these animals show.