Octopus RNA Editing: adenosine changes before neural proteins are made

In 2012, Sandra Garrett and Joshua Rosenthal compared potassium channels from cold-water octopuses with the corresponding channels from tropical species. The DNA encoding the two channels differed at only four positions. When the channels were expressed in frog oocytes, they behaved almost identically. The difference appeared after the genes had been copied into RNA. In polar species, RNA was often edited at a site in the channel pore, changing isoleucine to valine. The edited channel closed faster. Tropical species mostly did not edit that site. The researchers measured editing in eight species and found that its level varied with the water temperature where each species was collected.

The experiment shows that a biologically important change does not have to be fixed in DNA. A cell can edit RNA after copying a gene and before using that RNA to make a protein. This process is widespread among coleoid cephalopods, which include octopuses, squid, and cuttlefish. Transcriptome studies have found tens of thousands of A-to-I RNA editing sites. Many lie in protein-coding regions, and many occur in neural tissue.