Cephalopods - the family of invertebrate many-legged sea creatures to which octopuses, squids, and cuttlefish belong - are notorious for their astounding skills. Octopuses, in particular, seem to master Houdini-like escape artistry, as shown last year by Inky the octopus.
But cephalopod intelligence goes beyond getaway tricks and camouflage finesse. These smart creatures are capable of solving intricate puzzles, like unscrewing glass jars from the inside or learning to use a camera. Some octopuses even change their skin color to look like lion fish or sea snakes and thus scare off predators.
A new study featured on April 6 in the journal Cell indicates cephalopods possess even more complex abilities that allow them to disregard the normal rules of genetic information. The investigation revealed octopuses, squids, and cuttlefish are able to edit their genes, extensively rewriting their RNA to adapt to their environment.
Other fellow mollusks haven't reached this level of sophisticated neural development and still create proteins by converting DNA into RNA. This process allows certain genes to produce specific proteins. However, more advanced cephalopods are able to tweak their RNA, recoding it so that one gene can create several types of proteins from the same DNA.
Editing RNA Sequences
The research, authored by Joshua Rosenthal from the Marine Biological Laboratory in Woods Hole, Massachusetts, together with Eli Eisenberg and Noa Liscovitch-Brauer, from Tel Aviv University in Israel, continues the team's previous study on squids.
Two years ago, the scientists discovered these creatures can edit their RNA coding to diversify cellular protein production in their nervous system to a much greater extent than other animals.
Compared with fruit flies, which can edit only 1 percent of their RNA, squids are able to reconfigure more than 60 percent of their RNA coding regions.
Now, the team observed other cephalopods also have high levels of RNA editing. The new paper focuses on two species of octopus - Octopus vulgaris (the common octopus) and Octopus bimaculoides (California two-spot octopus) - the Doryteuthis pealeii squid, and one type of cuttlefish (Sepia oficianalis), which belong to the coleoid class of cephalopods.
These species were shown to have tens of thousands of RNA recoding sites, which allows the animals to edit their RNA frequently in almost half of their transcribed genes to expand the codes through which neurons produce proteins.
"Recoding by editing effectively creates a new protein sequence, and thus it's expanding the protein repertoire at the organism's disposal," says Eisenberg.
Proof Of Octopus Intelligence
This extraordinary ability is only present in coleoids, which are considered the smartest subclass of cephalopods. This special trait allows them to edit the RNA in their nervous system, tweaking the way their neurons function, explained Rosenthal.
In a past study, the scientist details how octopuses living in the Antarctic edit their RNA to beat the cold and keep their nerves firing at freezing temperatures.
The researchers also found that more primitive cephalopods, like the nautilus, have much lower rates of RNA recoding. This suggests coleoids are "fundamentally different," since many of their editing events "are highly conserved and show clear signs of selection," says Rosenthal.
Although the study doesn't establish these cephalopods have become smarter because of their advanced RNA recoding, it does indicate this ability "might have contributed to the exceptional intelligence."
Fewer DNA Mutations
Widespread RNA editing comes at a cost. Tweaking the codes at a cellular level means the editing site can't support DNA mutations, necessary in the natural process of evolution.
Most animals undergo changes in their DNA in order to evolve and adapt, but celoid cephalopods have prioritized RNA recoding instead, which means they have lower DNA mutation rates.
As Rosenthal explains, these animals are suppressing DNA mutations to maintain their flexibility of RNA recoding, essentially "giving up the ability to evolve in the surrounding regions."
To further investigate how the animals curb their DNA mutation rate in favor of RNA recoding, and what environmental conditions influence this process, Rosenthal plans to manipulate cephalopod genetics using the CRISPR-Cas9 gene editing technique.