Octopus Genome Sheds Light On Their Intelligence

An unusually high number of transposons could potentially be behind the octopus’ unique nervous system and camouflage abilities.

AsianScientist (Aug. 19, 2015) – A team of researchers from the Okinawa Institute of Science and Technology Graduate University (OIST), the University of Chicago, and the University of California, Berkeley have sequenced and analyzed the genome of an octopus species, making it the first cephalopod to be decoded. They published their findings in Nature. The genome-wide analysis was led at OIST by researchers in the Molecular Genetics Unit.

Imagine a skeleton-less creature with three hearts, with most of its nearly half a billion neurons distributed in eight tentacular arms. Each arm can regenerate like the mythical Hydra and has a mind of its own. This creature has the eerie capability of perfect camouflage and decorates its lair with leftovers of its prey.

Such is the bizarre reality of an octopus. They are cephalopods, a group of organisms including squid and cuttlefish that descended from a slow-moving, snail-like ancestor and became active, resourceful predators. Even though modern day snails, oysters and other mollusks have all evolved equally from this common ancestor in terms of time, octopuses somehow gained seemingly extraterrestrial capabilities. The secret lies in their genome.

Cephalopod brains are elaborations of the basic invertebrate brain, and have a completely different organization than what is found in humans and other vertebrates. Cephalopods emerged as predators in the ancient oceans over three hundred million years ago.

“They were the first intelligent beings on the planet,” quipped Nobel Laureate Dr. Sydney Brenner, founding president and distinguished professor of OIST.

Brenner was fascinated with the great sophistication of their nervous system and initiated the octopus Genome Project as the first of several important genome projects that have become a hallmark of OIST.

The large genome size of the octopus was previously believed to be the result of whole genome duplication events, which can also be seen in the genomes of vertebrates, including humans. Such events create additional genetic material for evolution to work with. The octopus genome, however, shows no evidence of such a dramatic event in its evolutionary history.

Besides recognizable genes, vast swathes of the genome consist of regulatory networks that control how genes are expressed in cells. In the octopus, nearly half of the genome was found to be composed of mobile elements called transposons, one of the highest proportions in the animal kingdom. Transposons replicate and move around with a life of their own, disrupting or enhancing gene expression and facilitating reshufflings of gene order. The researchers found many of them to be particularly active in the octopus nervous system.

Genes that are grouped together on chromosomes in other animals were dispersed in the octopus genome, likely as a result of transposon activity. The “Hox” genes, involved in embryonic development in all animals, are a particularly dramatic example. Although clustered together in most animals, including other mollusks, they are scattered in snippets in the octopus, presumably enabling the evolution of the versatile cephalopod body plan.

The sequenced genome also provides a reference for scientists studying cephalopods to investigate other species of these exotic animals. Future inquiry also relates to cephalopod genes and regulation relevant to the development and functioning of the nervous system. As some of those genes are already active at the embryo stage, their expression can be biochemically interfered with. Researchers can then watch out for divergences in the grown organism.

“To do all this, we need to be able to raise animals in the lab and have a better idea of what their normal behavior is, so we can recognize what has changed when a gene is deleted or disrupted. This is a big project, the kind that can only be done in a multidisciplinary environment like OIST,” said Dr. Daniel Rokhsar, head of OIST’s Molecular Genetics Unit.

One reason the octopus fascinates scientists is that its brain became organized to be able to carry out such incredible, complex tasks without adopting the principles of the vertebrate brain. Further examination will tell if the building blocks of its nervous system are as radically different from those of vertebrate landlubbers like us, as the octopus’s abilities suggest.

This is not as unlikely as it sounds. Even if the octopus evolved in a completely different ecosystem, evolution can have only so many solutions to a given problem. If similarities are in fact found, this would significantly alter our perspective on the emergence of life elsewhere in the universe.

The article can be found at: Albertin et al. (2015) The Octopus Genome and the Evolution of Cephalopod Neural and Morphological Novelties.


Source: OIST.
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