Scientists Sequence Genome of California Two-Spot Octopus

“What is similar among all cephalopods is probably important to being a cephalopod”, said the founding president of the Okinawa Institute of Science and Technology Graduate University in Japan Dr. Sydney Brenner.

“The octopus appears to be utterly different from all other animals, even other mollusks, with its eight prehensile arms, its large brain and its clever problem-solving capabilities”, said Clifton Ragsdale, one of the leaders of the genome-sequencing project from the University of Chicago. Octopuses, along with squids, cuttlefish and nautiluses, are cephalopods, an order of predatory mollusks with an evolutionary history of more than 500 million years, long before plants moved onto land.

As it turns out, the octopus genome is nearly as large as a human’s and actually contains more protein-coding genes: 33,000, compared with fewer than 25,000 in humans.

As reported in Nature, the team uncovered genomic features that likely played a role in the evolution of traits such as large complex nervous systems and adaptive camouflage, including hundreds of octopus-specific genes.

“The octopus nervous system is organized in a totally different way from ours: The central brain surrounds the esophagus, which is typical of invertebrates, but it also has groups of neurons in the arms that can work relatively autonomously, plus huge optic lobes involved in vision”, study co-author Daniel Rokhsar, a professor of genetics and genomics at the University of California, Berkeley, said in a statement.

Scientists have cracked the octopus genome, and it’s unlike anything they’ve ever seen before. In the future, he and his colleagues plan to sequence several squid species and the Okinawan octopus, which they hope will become a model organism for studying cephalopod biology.

The octopus’s genome is almost the size of the human genome and much larger than those of other sequenced invertebrates such as snails or oysters.

The researcher team approximates that the octopus genome has the size of 2.7 billion base-pairs.

The researchers uncovered evidence of widespread RNA editing, which allows the octopus to alter protein sequences without changing underlying DNA code. Scientists are especially interested in one set of genes called protocadherins. How does it control its 8 flexible arms and over 1000 suckers?

The team had to first obtain a species of octopus that is very easy to breed in laboratory conditions.

“Octopuses typically pounce on their prey or poke around in holes until they find something”.

Six octopus-specific reflectins, genes involved in light manipulation and camouflage, were identified.

Albertin and Ragsdale are now studying the molecular and genetic mechanisms responsible for the development of the octopus, particularly its brain. The large size of the octopus genome was initially attributed to whole genome duplication events during evolution.

The scientists explain that the octopus has 168 protocadherins (more than twice as many as mammals), which are genes regulating the development of neurons and the short-range interactions between them.