Octopuses can adapt to changes in temperature by tweaking their genetic code to alter the proteins that are made in their nerve cells.
Previous research has established that cephalopods, such as squids and octopuses, possess an unparalleled ability to edit their RNA. These “messenger” molecules carry a copy of genetic instructions from DNA to parts of the cell where proteins are made. But it was unclear why the animals do this or what effects it has.
Joshua Rosenthal at the Marine Biological Laboratory in Woods Hole, Massachusetts, and his colleagues tested how California two-spot octopuses (Octopus bimaculoides) responded to changes in water temperature in tanks.
They gradually shifted the temperature to around 13°C (55°F) for one group and 22°C (72°F) for another group. The octopuses in the colder tank made more than 13,000 edits to their RNA that led to changes in the resulting proteins.
“It’s tempting to think they’re doing this to acclimate to a changed environment and this is where we show that they can do that, at least to one environmental condition, which is temperature,” says Rosenthal.
Many animals, including humans, have enzymes that can swap letters in RNA to change those instructions. However, for the majority of animals, most edits take place in non-coding RNA – that is, RNA that isn’t translated into a protein. These edits may still be useful in other ways; for example, they can affect how cells in our immune system develop or activate.
“What is interesting about cephalopods is that they recode proteins in a magnitude that is much higher than any other species or any other family of animals that we know,” says Eli Eisenberg at Tel Aviv University in Israel, who also worked on the study. He says the reason for this isn’t completely known.
Two of the proteins that were altered significantly in response to temperature were kinesin-1 and synaptotagmin, which are both critical for the functioning of the nervous system.
Kinesin-1 is responsible for transporting chemical cargo across long microtubules inside neurons, which can extend to a metre in length. As they travel, kinesins look like they are walking with tiny feet. The RNA editing changed part of the kinesin’s “foot” where it connects to the microtubules, making it travel more slowly at lower temperatures.
Synaptotagmin is found at connections between neurons called synapses, where it senses calcium levels and triggers the release of chemical messages from one cell to another. The RNA editing caused synaptotagmin proteins to have a lower affinity for calcium at lower temperatures.
Eisenberg says it is too early to know how these changes might make octopuses better adapted to the cold. “Thousands of proteins are different in the cold and warm, so to understand how they all work in concert to give the octopuses resilience to temperature changes is very complicated.”
However, the researchers think the timescale at which the changes occur suggests these modifications are better suited to seasonal temperature differences, rather than sudden changes, such as those caused by water currents.
Jin Billy Li at Stanford University in California says the exact drivers behind these changes remain a mystery. “I think it’s fair to say that we don’t know the mechanism of why the temperature-dependent changes happen.”