Octopus genome insights

Carrie Albertin, University of Chicago


Good morning. I recently completed my PhD working at University of Chicago. I want to thank the organizers for inviting me here. It's exciting to be here at the dawn of new technology promising to open up a whole new world of technology. Genome sequencing led to many new tools, which allows us to sequence 100s of animal genomes. If we look at the over 30 animal phyla, there has been a burst of sequencing from many groups. There are more than 300 chordate genomes, like frogs, fish, mammals and birds, and many athropod genomes like Drosophila melanogaster, and some nematode genomes including C. elegans... but if we consider animal diversity as a whole, we can see that the bulk of the work is restricted to 2 of the 3 main animal groups. There's a handful of sequences available for jellyfish and sponge, but mostly in bilaterally symmetrical animals, much of it found in duoderas, chordates and dyzazoans like arthropods and nematodes.

Lopatrocaza contains half of all animal phyla but have been relatively underserved by the boom in genome sequencing. So I want to tell a story about one of the genomes, found in the molluscs. This is the genome of the two spot octopus shown here.

Why octopus

They are cool. They have many features not found anywhere else, like the crown of suckers lining their arms, going from beak to mouth. The espophagus goes through their brain, and their mantle contains their visera, they have 3 hearts. Cephalopods have remarkable behavior, like changing the color and texture of their skin to match their background.

They have a lot of remarkable behavior, governed by large nervous systems. They have the largest invertebrate nervous systems. Here we can see the brain of an adult mouse, and shown at the same scale, here's an adult octopus, a small to medium size octopus. Here we can see the brain, and on either side there are large optic lobes connecting to the eyes which would be on either side of it. This is less than half of the octopus nervous system, and the rest run down each of their 8 arms. These nervous systems are put together rather differently, but it gives us an excellent example of convergent evolution for how genomes are put together.

From decades of research in mice, there are a number of genes involved in vertebrate nervous system setup. Mostly cell adhesins. There are membrane domains, intracellular domains and a few others. PCDHalpha, EC, TM, IC. They can combine and mix and match to create a divversity of signals outside of neurons that help develop neuronal circuits in vertebrate brains. Cadherins. There's the alpha cluster, beta cluster, and gamma cluster. Vertebrates have 53 clusters of cadherins in the ... protocadherins in the human genomes. In sea urchins, we find only one in their genome. Searches in the fly and nematode genomes have found none; so the last common ancestor had a single protocadherins which was lost in one lineage, but greatly expanded in invertebrates. There are more than 160 protocadherins in the octopus genome, and we were really surprised about that.

When we consider the relationship of different protocadherins to each other, they cluster based on their lineage. The octopus protocadherins largely segregate from other cephalopods like the boston market squid. The expansion of protocadherins in these lineages might be independent from each other.

In addition, octopus protocadherins are found in genomic clusters. This is an unexpected role for protocoadhersins in setting up large nervous systems. The convergence we see at the morphological level between cephalopods and invertebrates-- providin fundamental insights into nervous system function.

I'd like to thank my dissertation advisor.