Meeting Abstract
Cephalopod molluscs (Nautilus, Loligo, Octopus, Sepia) are powerful models for comparative biology and neuroscience. The complexity of their nervous systems ranges from simpler cords (Nautilus) to one of the most intricate brains of the animal kingdom in Octopus. Of all cephalopod innovations, the most extraordinary structure is the vertical lobe (VL), where we find cell circuits modulating the most advanced learning and memory in all invertebrates. This is an analog of hippocampus in mammals and a perfect example of convergent evolution. To examine this structure and its cellular components, we sequenced neuronal transcriptomes of key model cephalopods from the VL and from the surrounding circuitry. We compared these datasets to one another and to sequenced genome and transcriptomes of the gastropod mollusc, Aplysia. This approach has allowed us to identify conserved neuronal genes and numerous genomic innovations within molluscs. For example, we have identified in cephalopods approximately 50% all known Aplysia neuropeptides (NP) in addition to novel cephalopod-specific NPs. Of all identified cephalopod NPs, we have cloned and localized expression of 17 in Octopus vulgaris, and 13 in the squid Loligo pealei. Additionally, in our transcriptome data, we have identified in Octopus 16 NPs in the VL that may play a role in cell signaling during memory function, four of which have been validated by in-situ localization: FLRIamide, Bradykinin, Conopressin, and Buccalin. This comparative anatomical and genomic approach provides unique opportunities to reconstruct ancestral neuronal lineages, identify conserved cell types across species, and reveal trends in evolution within neural circuits.
