What the octopus genome can tell us

Author: Shweta Ramdas

Editors: Irene Park, Ada Hagan, Alisha John

The team at MiSciWriters certainly finds cephalopods fascinating, and we aren’t alone. Last year, the octopus (Octopus bimaculoides) was added to the growing list of organisms whose genome sequence is known.

Octopuses belong to a class of organisms called cephalopods, which literally means ‘head-feet’ (members of the cephalopod family have a head and tentacles or arms). These tentacles enable the creatures to do some very clever maneuvering, such as escaping their aquariums to eat crabs outside their tanks. It’s no surprise then that these are the most intelligent amongst invertebrates and now new information about the octopus genome can tell us more about these fascinating creatures.

Octopuses have a unique nervous system organization. A control system of around 400,000 neurons controls each of their eight tentacles, guiding movement without any command from the brain.

Understanding their nervous system could give us new insights into intelligence and how complex nervous systems (like ours!) develop.

While sequencing the octopus’ genome, the authors not only sequenced the creature’s genome, but also measured which genes were turned on in different tissues of the octopus. This information helps researchers speculate on the function of interesting genes based on where they are turned on. For instance, if a previously unknown gene was expressed solely in the suckers of octopuses, we would predict that its function is important to a feature of suckers and then test that hypothesis.

The researchers found that the octopus genome is nearly as large as that of humans, but that octopuses have about 33,000 genes, which is about 13,000 more than humans! Some gene families (groups of genes that perform similar functions) can be duplicated or expanded in some species, which might be one reason octopuses have so many more genes than we do.

An expansion of an existing gene family allows for diversification of gene function, where multiple genes perform similar, but not identical, functions. For instance, each gene in a gene family could be turned on in a different cell type, allowing specialized functions in different tissues. Understanding which gene families are duplicated can help us understand the functions that are important enough to warrant this expansion.

The authors found an expansion in the octopus ‘protocadherin’ gene family: a group of genes involved in neuron development and the maintenance of connections between different neurons, which is important for signal transmission in the brain. The octopus genome encodes 168 protocadherin genes compared to just 17-25 found in oysters, another invertebrate. Interestingly, vertebrates also show an expansion of this gene family. The expanded protocadherin family in octopods could be a key to their high levels of intelligence.

This gene family expansion was also seen in squids – another class of cephalopods that are believed to be intelligent – but has evolved in a separate event: it’s not the same duplication event that gave rise to the expansion in these two species! This is quite remarkable, because it means that this protocadherin expansion is advantageous enough for it to have evolved in the cephalopods twice (a phenomenon termed convergent evolution).

The octopus genome is so unusual and bizarre compared to the other sequenced genomes (other features include specialized receptors for ‘taste’ on their suckers!) that the one of the authors said, “It’s the first sequenced genome from something like an alien.” Further comparative and functional studies on the octopus genome will only help us understand what genes are important in an organism’s intelligence, which is key to our understanding of the evolution of intelligence. To find out more, check out this video from Nature: https://www.youtube.com/watch?v=634j7m5U5II.

About the author

Shweta is a graduate student in Bioinformatics at the University of Michigan. Her research involves computational methods to understand the genetic basis of psychiatric disease. Her undergraduate degree is from the National University of Singapore where she studied computational biology. Outside of research, Shweta enjoys reading, yoga, and figuring out the genetic basis for being a muggle. Follow Shweta on Twitter.

Read all posts by Shweta here.

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