Octopuses, squid and cuttlefish carry one of the most unusual genomes in the animal kingdom, and a team at the University of Vienna now argues that an ancient rearrangement of their DNA put distant stretches of the genome in contact and may have helped their nervous systems evolve. The study, published in Nature Communications, is careful to call this a plausible mechanism rather than proof that the shuffle made octopuses smart.
Lead author Thea Rogers, of the university’s Department of Neuroscience and Developmental Biology, says the point of the work is that a genome is more than a list of genes. Where stretches of DNA sit relative to each other inside the cell nucleus can decide which genes switch on, and that geometry looks different in the coleoid cephalopods than in other animals.
Folded DNA and the idea of regulatory entanglement
“The genome isn’t just a sequence of genes. It’s folded into a complex three-dimensional structure,” Rogers said in the University of Vienna announcement, adding that understanding how that structure evolves is becoming increasingly important. The researchers reconstructed the three-dimensional organization of the genome in octopus, squid and cuttlefish and compared it with patterns of gene activity, looking for places where physical contact lined up with regulation.
Their central claim concerns an event hundreds of millions of years ago. A large-scale reorganization moved previously separated chromosome regions next to one another, and once such regions touch, they can influence each other’s gene activity. Over time those interactions become interconnected, which the team calls regulatory entanglement. According to the ScienceDaily report on the work, that arrangement may let a genome produce new gene expression patterns while keeping essential functions intact.
Stable domains, flexible loops near neural genes
Not everything in the folded genome moved. Large chromatin domains, the big neighborhoods of DNA, stayed stable over long evolutionary periods. The finer structures behaved differently: smaller chromatin loops varied between species, tissues and developmental stages, and many sat near genes tied to nervous system development and function. Stable architecture with flexible detail is the pattern the authors read as a regulatory landscape that is distinct to coleoid cephalopods.
An earlier preprint of the project, posted to bioRxiv, gives a sense of the scale of the data. It compared three species, the Hawaiian bobtail squid Euprymna scolopes, the common cuttlefish Sepia officinalis and the California two-spot octopus Octopus bimaculoides, and dated the coleoid group to about 450 million years. It counted 329 chromatin loops in whole bobtail squid embryos, 912 in cuttlefish and 663 in the octopus, and found just three loops conserved across all three species.
That small shared set matters to the argument. Most loops differ from species to species, which fits the idea that fine-scale contacts keep changing while the large framework holds. The preprint also notes that genomes in this group are large: about 2.7 gigabases in some octopuses and more than 5 gigabases in some squid and cuttlefish. Figures from a preprint can shift between drafts and the published paper, so they are best read as an outline of the approach.
The preprint describes how the contact maps were made. The team applied a technique called Micro-C to whole embryos and dissected tissues, then layered on chromatin accessibility data and gene expression data, and used a scallop and a Nautilus as outgroups, animals outside the group that give a baseline for what the older arrangement looked like. A gene-editing test in a related bobtail squid, Euprymna berryi, deleted a stretch of roughly 1,000 DNA letters from an intron of the gene Quaking B to probe what a single regulatory region does.
Limits of the evidence
The caveat comes in the study’s own words: “The results do not establish that these DNA changes directly caused the evolution of cephalopod intelligence.” The work offers a mechanism that fits the evidence, and the authors argue that three-dimensional genome organization actively shapes evolution rather than being a byproduct of it, but a link from folded DNA to behavior would need experiments that test specific contacts.
The full author list reads Thea F. Rogers, Jessica Stock, Natalie Grace Schulz, Gozde Yalcin, Simone Rencken, Anton Weissenbacher, Tereza Clarence, Darrin T. Schultz, Clifton W. Ragsdale, Caroline B. Albertin and Oleg Simakov, and the paper is catalogued under its Nature Communications DOI. Readers following animal genetics can find related items in ScienceDaily’s new species section, though the central finding here is about structure, not new species.
What remains open is how much of cephalopod cognition traces back to this layout. The honest summary from Vienna is a proposal with a mechanism attached: an ancient reshuffle changed which parts of the genome touch, and the loops near nervous system genes are where the animals could have gained room to experiment. The reports on the study do not tie any particular loop to a particular behavior, which leaves the intelligence question as the next thing to test.
This article was produced with the assistance of AI and reviewed by Morning Overview editors prior to publication.
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