RNA editing helps octopuses cope with the cold

The ocean can be a cold place to call home. Mammals like seals stay warm by enveloping themselves in a layer of thick fur and blubber. Cephalopods — the group of (mostly) ultrasmart mollusks that include squid and octopuses — don’t have that luxury.

Instead, some octopuses and squid cope by altering their bodies on the molecular level.

When water temperatures inside their tank dropped by 10 degrees Celsius, California two-spot octopuses (Octopus bimaculoides) changed what proteins they produce by editing vast swathes of their own RNA, researchers report June 8 in Cell.

The “astounding high levels” of molecular editing — most of which occurs in the nervous system — could help octopuses’ brains function when temperatures plunge, says Joshua Rosenthal, a molecular neurobiologist at the Marine Biological Laboratory in Woods Hole, Mass.

Another study in Cell, also published June 8, found a similar effect of temperature on RNA editing in California market squid (Doryteuthis opalescens). 

Scientists have known for over a decade that cephalopods are masters of RNA editing (SN: 5/19/23). DNA holds the instructions to make proteins, one of the key building blocks of the body. But it relies on messenger RNA — or mRNA — to shuttle those instructions out of the cell nucleus and to the proteins responsible for building other proteins.

Usually, mRNA faithfully copies these instructions. But sometimes, mRNA is edited, which can change how those proteins behave or even what proteins are made. For instance, about 3 percent of mRNA in humans has the capacity to be edited, though even fewer are edited.

Octopuses and squid take this editing to extremes — changing thousands of mRNA.

What sets off this storm of editing isn’t always obvious. Previous research suggested that temperature might be a trigger. To test this, Rosenthal and his colleagues either heated or cooled the tank temperature of octopuses and looked to see what proteins they produced in their brains. While heat set off very little editing, octopuses that experienced cool temperatures altered over 20,000 mRNA sites, which changed around a third of the instructions for making proteins.

This fury of editing started in the space of only a few hours — probably changing the behavior of octopus brains. For instance, the team found that mRNA editing caused kinesin, a protein that shuttles cargo in nerve cells, to slow its movement. Why this happens is unknown, but it might help the cargo-carrying protein harmonize its movements with other processes in the cell if they too become sluggish, Rosenthal says.

Cold-exposed squid also edited their kinesin — though in their case, the changes helped the proteins move greater distances inside cells, says Kavita Rangan, a molecular biologist at the University of California, San Diego who conducted the squid study.

Previous studies have shown that disease can cause RNA editing. This “truly amazing body of work” shows that environmental changes, like temperature, can also shape mRNA editing, says Heather Hundley, an RNA researcher at Indiana University Bloomington who was not involved with the research.

Octopuses have long captured the public imagination through their intelligence and camouflage, says octopus study coauthor Matthew Birk, a cephalopod biologist at Saint Francis University in Loretto, Penn. “We’re now learning that they are strange not just on the outside, but down to the molecular level.”