Octopus, squid, and cuttlefish are famous for engaging in complex behavior, from unlocking an aquarium tank and escaping to instantaneous skin camouflage to hide from predators. A new study suggests their evolutionary path to neural sophistication includes a novel mechanism: Prolific RNA editing at the expense of evolution in their genomic DNA. The study, led by Joshua J.C. Rosenthal of the Marine Biological Laboratory (MBL), Woods Hole, and Eli Eisenberg and Noa Liscovitch-Brauer of Tel Aviv University is published this week in Cell. The research builds on the scientists’ prior discovery that squid display an extraordinarily high rate of editing in coding regions of their RNA — particularly in nervous system cells — which has the effect of diversifying the proteins that the cells can produce. (More than 60 percent of RNA transcripts in the squid brain are recoded by editing, while in humans or fruit flies, only a fraction of 1 percent of their RNAs have a recoding event.)
“This shows that high levels of RNA editing is not generally a molluscan thing; it’s an invention of the coleoid cephalopods,” Rosenthal says. In mammals, very few RNA editing sites are conserved; they are not thought to be under natural selection. “There is something fundamentally different going on in these cephalopods where many of the editing events are highly conserved and show clear signs of selection,” Rosenthal says.