Octopus: Stranger than any "Sci-fi Alien"

The octopus is a creature so weird that author Sy Montgomery says “no sci-fi alien is so startlingly strange”. It has 3 hearts, parrot like beaks, 8 arms that can taste (yes, taste) the world, squirt ink, is poisonous, and can change both texture and form. (Google up videos for the kinds of spaces through which it can squeeze through, thanks to its ability to change form. It will blow your mind).

As if such physical capabilities weren’t enough, an octopus at a genetic level, is “really weird”, writes Ed Yong. But first, a recap of how DNA works:

“Genes encode instructions in the form of DNA—in the sequence of four building blocks represented by the letters A, C, G, and T. For those instructions to be used, the DNA must first be transcribed into a similar molecule called RNA, which contains roughly the same building blocks. The RNA is then translated and used to build proteins—the molecular machines that carry out all the important jobs inside our cells. So DNA stores information, RNA carries it, and proteins are the result of it.”

At least, that’s how things work in most life forms, humans included. But the “intelligent coleoid cephalopods—octopuses, squid, and cuttlefish” are different on that front. How?

“The RNA often gets altered before it’s used to make proteins.”

Some of the RNA edits are small, others are big. You might remember that a lot of DNA is called “junk DNA”, i.e., DNA that isn’t translated into proteins. If only junk DNA sequences get edited by the RNA, you’d be right in saying “So what? Such edits make no difference to the animal since they won’t get converted into proteins anyway”. In fact, such junk DNA edits happen in most animals.

But the octopus (and others in that family) are different: RNA edits happen to DNA areas that do get translated into proteins! And such RNA edits “disproportionately affected proteins involved in its nervous system”. But is that a causal relation? Do high RNA edits cause “complex brains and extraordinary behavior”? Or is that just coincidence?

While digging into that question, researchers found that the RNA edit “algorithms” are almost hard-coded in their logic, i.e., they look for a specific DNA sequence and edit only certain letters within that sequence. Flip that around, and it means that the RNA edits can work only if the underlieing DNA sequence doesn’t change. So researchers checked if those DNA sequences have changed (evolved) much over time. What did they find?

“These sites have been preserved over hundreds of millions of years of evolution… their genomes are rigid and stagnant.”

So it would suggest that RNA edits do cause benefits for the species. If it didn’t (or didn’t matter either way), wouldn’t the underlieing DNA have changed?

Well ok, but is this just a different way to evolve? “Regular” evolution involves changes to the DNA, whereas this model seems to involve editing the DNA on the fly. So is RNA editing just a different model? Or is it superior than “regular” evolution in any way?

The obvious advantage of RNA editing is that it is on-the-fly editing:

“From the same gene, they could produce proteins that, say, work better in hot temperatures or cold ones. And such changes would be temporary—the creatures could turn them on or off depending on the circumstance.”

Then again, if it was such a huge step forward, shouldn’t most of life been overrun by this “superior” form of evolution?

And so the debate continues… a fascinating area for further research.