The genome sequence, which was produced through collaboration between scientists from the United States, Germany and Japan, was published Wednesday in Nature.
"The octopus has a large and complex genome, so this was no trivial task," study author Caroline Albertin, a graduate student at the University of Chicago, told The Post. First the researchers had to find an octopus that was easier to raise in a lab than most. The smallish California two-spot octopus, which produces hatchlings that immediately act much like adults, did the trick. But the work itself, Albertin said, took several years -- and many hours on the phone with international colleagues.
The results yield a couple of interesting surprises: For starters, Albertin and her colleagues found that the relatively massive genome of the octopus (2.7 billion base-pairs for this particular species, compared to around 3 billion in humans) wasn't due to duplication, as some researchers have suggested. In other words, the octopus never doubled up its genes, as some organisms have been known to do. But it somehow managed to grow a much larger set of genes than many of its marine relatives.
With no tell-tale signs of whole genome duplication, the researchers say, the octopus must have instead duplicated specific regions of its genetic code -- and acquired totally novel genes -- over the course of its evolution.
One of those specific gene expansions is a "smoking gun" that may help explain why octopuses are so intelligent. The octopus had an unusually high number of genes called protocadherins. In other animals, those are known to regulate the development of neurons and the interactions between them.
The octopus genome was found to contain 168 protocadherin genes, which is around 10 times what you'd expect in an invertebrate, and twice the number usually found in mammals.
"A lot of work will have to be done to puzzle out the questions raised by this paper," Albertin said. "But this gene family is an interesting genomic smoking gun."
The octopus also appears to have a large number of transposons, or "jumping genes" that are capable of rearranging their position in the genome. In some cases, the researchers said in a statement, the sequence looked like an invertebrate genome that had been pulsed in a blender, with familiar genes ending up in unfamiliar places -- where they may be serving unfamiliar functions.
Until now, Albertin said, studying octopuses at the molecular level has been difficult. Octopuses diverged from better understood mollusks over half a billion years ago. Even squids, fellow cephalopods who are quite close to octopuses on the family tree, parted ways with octopuses about 270 million years back.
So there's really been no telling what genes might power the unique behavioral and physiological traits of the creatures.
"A genome represents the molecular toolbox available to an animal, so it gives you a catalog of all of the genes that there are, and where they’re expressed," Albertin said. "Now that we have that toolbox, we can start to pick out different gene groups and figure out what they're actually doing in these bizarre animals."
Christine Huffard of the Monterey Bay Aquarium Research Institute, who wasn't involved in the study, is eager to see what the data will yield.
"This will guide studies that until right now, today, we might not have thought were possible," Huffard said. "Next month or a year from now we’ll hopefully be doing much more complex behavioral studies because of it."
The team that produced the sequence has their own set of questions to answer. Albertin is interested in the way octopuses develop from single cells to fully-fledged hatchlings, and fellow study author Yan Wang, also of the University of Chicago, told The Post she'd be studying how the octopus brain controls complex behavior, especially in relation to mating and reproduction.
"Everyone who came to this project came in with their own agenda, their own question," Albertin said. "We're just excited to see the cephalopod enter the post-genomic era."