Today, important clues about the anatomy and evolution of the mysterious giant squid (Architeuthis dux) are revealed through publication of its full genome sequence by a University of Copenhagen-led team that includes scientist Caroline Albertin of the Marine Biological Laboratory (MBL), Woods Hole. Giant squid are rarely sighted and have never been caught and kept alive, meaning their biology (even how they reproduce) is still largely a mystery. The genome sequence can provide important insight.
Led by Rute da Fonseca at University of Copenhagen, the team discovered that the giant squid genome is big: with an estimated 2.7 billion DNA base pairs, it's about 90 percent the size of the human genome. Albertin analyzed several ancient, well-known gene families in the giant squid, drawing comparisons with the four other cephalopod species that have been sequenced and with the human genome.
She found that important developmental genes in almost all animals (Hox and Wnt) were present in single copies only in the giant squid genome. That means this gigantic, invertebrate creature -- long a source of sea-monster lore -- did NOT get so big through whole-genome duplication, a strategy that evolution took long ago to increase the size of vertebrates. So, knowing how this squid species got so giant awaits further probing of its genome. Albertin also identified more than 100 genes in the protocadherin family -- typically not found in abundance in invertebrates -- in the giant squid genome.
Lastly, she analyzed a gene family that (so far) is unique to cephalopods, called reflectins. "Reflectins encode a protein that is involved in making iridescence. Color is an important part of camouflage, so we are trying to understand what this gene family is doing and how it works," Albertin says. "Having this giant squid genome is an important node in helping us understand what makes a cephalopod a cephalopod. And it also can help us understand how new and novel genes arise in evolution and development."
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