Emergence of novel cephalopod gene regulation and expression through large-scale genome reorganization.

Coleoid cephalopods (squid, cuttlefish, octopus) have the largest nervous system among invertebrates that together with many lineage-specific morphological traits enables complex behaviors. The genomic basis underlying these innovations remains unknown. Using comparative and functional genomics in the model squid Euprymna scolopes, we reveal the unique genomic, topological, and regulatory organization of cephalopod genomes. We show that coleoid cephalopod genomes have been extensively restructured compared to other animals, leading to the emergence of hundreds of tightly linked and evolutionary unique gene clusters (microsyntenies). Such novel microsyntenies correspond to topological compartments with a distinct regulatory structure and contribute to complex expression patterns. In particular, we identify a set of microsyntenies associated with cephalopod innovations (MACIs) broadly enriched in cephalopod nervous system expression. We posit that the emergence of MACIs was instrumental to cephalopod nervous system evolution and propose that microsyntenic profiling will be central to understanding cephalopod innovations.