Octopuses adapt to temperature shifts by rewiring brain

(CN) — From escaping tanks for stolen midnight fish snacks, opening jars, and playing little tricks on biologists, what can’t octopuses do? They can even, according to a new study, rewrite their genetics to accommodate for environmental changes.

Like many other marine creatures, octopuses are cold-blooded and unable to thermoregulate; they rely on the outside environment to maintain internal temperatures. It’s the reason why cold-blooded animals are sometimes seen basking in the sun or scurrying into the shade to preserve consistent body temperatures. This acclimation is necessary for the animals to maintain brain and other bodily functions.

According to a study published Thursday in the journal Cell, “Phospholipid membranes are one of the most temperature-sensitive cellular structures, and cells must actively modulate their fluidity to compensate for temperature.” In octopuses, which are noted for an extremely high level of intelligence amongst invertebrates, with a cleverness comparable, some say, to dogs, investing in continued brain function is imperative.

Researchers report in the study that octopuses and other cephalopods can regulate body temperatures uniquely by using messenger RNA, the molecule that provides the genetic blueprint for protein creation, to recode neural protein production based on temperatures in their environment.

RNA recoding allows for an organism to shift how they express proteins with greater variability in timing and location. Unlike alterations in DNA, RNA editing can happen temporarily and relatively quickly.

The feature of RNA editing is not specific to cephalopods — humans, for example, have millions of editing sites — but the level of recoding demonstrated by the study is unique to octopuses, squid and cuttlefish. Only roughly 3% of human messages harbor weak recoding sites, compared to cephalopods which can recode a majority of neural proteins. This prolific ability to recode has left scientists wondering how they might use this capability to adapt to environmental changes.

Using the California two-spot octopus as a sample, researchers investigated the cephalopod’s genetic reaction to shifting water temperatures and found that the octopus would undergo RNA editing to better protect sensitive brain cells.

The wild-caught octopuses were placed into tanks of either warm (22C/71.6 F) or cool (13 C/55.4 F) water — mimicking temperatures during summer and winter in their natural habitat along the Pacific Coast near California and Mexico — at the Marine Biological Laboratory in Woods Hole, Massachusetts. After several weeks of acclimation, researchers sequenced and compared genetic transcripts for RNA editing across 60,000 editing sites in their genomes.

Researchers write that their “data support the idea that cephalopod editing is under positive selection and leads to phenotypic advantage. Individual recoding sites can directly affect protein function.”

It was discovered that recoding occurred at about one-third of those editing sites at colder temperatures, and specifically affected neural proteins. Only about 1% of editing sites demonstrated higher editing levels at the warmer temperature.

According to the study, “These trends suggest that cold-induced editing favors subtle, common amino acid substitutions over rare, drastic changes.”

Researchers also determined that similar trends occurred for octopuses living entirely in the wild. Octopuses caught at the beginning and end of the winter and summer months followed a similar pattern of robust cold-driven editing not only for the California two-spot variety, but also for the closely related Verill's two-spot octopus.

Research into the time frame of RNA editing revealed the RNA editing could happen swiftly, as researchers, now using juvenile two-spot octopuses, gradually raised and lowered temperatures in the water tanks to evaluate how much RNA editing was occurring before the temperature changes, immediately after, and several days later.

“Statistically significant changes in editing levels were observed both during the 20-h temperature shift and at nearly every time point afterward during both warm-to-cold and cold-to-warm experiments,” study authors wrote, “suggesting that a new steady state had been reached within 4 days at both temperatures.”

It is still unclear to scientists what the mechanism behind the RNA editing is, especially as to why colder temperatures prompt a greater reaction. Researchers also express an interest in seeing if RNA editing can respond to environmental changes beyond temperature shifts.

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