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Octopus Genome Offers Insights Into One Of Ocean's Cleverest Oddballs

A juvenile California two-spot octopus (Octopus bimaculoides).
Michael LaBarbera/Nature
A juvenile California two-spot octopus (Octopus bimaculoides).

Scientists have just sequenced the first genome of an octopus, and it was no trivial task.

"The octopus has a very large genome. It's nearly the size of the human genome," says Carrie Albertin, a biologist at the University of Chicago.

As technology to sequence DNA has gotten faster and cheaper, scientists have unraveled the genes of all kinds of creatures. But until now, no one had done an octopus — despite its obvious appeal as one of the weirdest animals on Earth.

After all, these critters can regrow lost arms! Change the color of their skin! They can unleash a cloud of ink and zip through the water using jet propulsion! Plus, they're surprisingly smart.

Scientists want to understand all this at the level of DNA. And after a team at the University of Chicago started sequencing a particular octopus species, they heard that a group in Japan, at the Okinawa Institute of Science and Technology, had taken on the exact same challenge.

"When we found this out, we joined our efforts together," says Albertin.

Wednesday, in the journal Nature, they report on the genetic code of Octopus bimaculoides — aka the California two-spot octopus. This hardy creature sports two blue spots behind its eyes, and it doesn't seem to mind living in the lab.

"They're not very large," says Albertin. "They can squish down to about the size of a tennis ball."

And looking at their genes is starting to reveal some octopus secrets.

For example, scientists had thought the octopus genome got so big because at some point the whole genome just copied itself. But no, says Albertin. "As we started to dig into the data, we were seeing more and more signs that there was no duplication."

What's more, they saw a massive expansion in a family of genes that's involved in setting up brain circuits. These genes have been studied in mice and were previously thought to be numerous only in animals with backbones.

"We were really surprised as we were poking through the octopus genome to see that there were just 150 [or] 160 of these genes," Albertin says. She says they're completely absent in the invertebrates that scientists normally work on, like flies or nematode worms.

The researchers also took samples of tissue from a dozen different body parts, to see what specific genes were turned on in them. In the arm's suckers, they saw activity in genes that are normally related to signaling between neurons in other animals — although the octopus had altered versions of these genes.

"So they might be doing something related to sucker function," says Albertin. The suckers on octopus arms are chemosensory, she notes, so they can taste. "Maybe, possibly, these are involved in that."

The goal, Albertin says, is to take this whole genetic toolkit and figure out how it's used to make an octopus. And she expects to get some help by comparing the octopus to other strange ocean creatures — such as the cuttlefish — because scientists are busy working on those genomes too.

Copyright 2021 NPR. To see more, visit https://www.npr.org.

Nell Greenfieldboyce is a NPR science correspondent.