Meeting Abstract
Euthyneura molluscs provide a unique opportunity to study the homology and evolution of nervous systems on a cellular level because these animals have the largest neurons in the animal kingdom. Since the Cambrian expansion, molluscs have undergone multiple independent nervous system centralization events where clusters of neurons have fused or been lost. In contrast, the serotonergic Metacerebral Cells (MCCs) are functionally and morphologically conserved across 380 million years of evolution, the longest traced single neuron homology in any system! Yet, little is known about the genetic homology shared between Euthyneura. To address this, we compared CNS, ganglia, and single neuron transcriptomic data from Pleurobranchaea californica to the genomic and transcriptomic data from the classic Euthyneura neuroscience model Aplysia californica and to other close and distant relatives. BUSCO analysis revealed 94% conservation of metazoan single copy orthologs in the P.californica hybrid assembly suggesting that we have constructed a reference transcriptome of near genome quality. Neuropeptides are diverse fast-evolving signal molecules that regulate physiological processes and behavior. Manual annotation of neuropeptides revealed that out of the Euthyneura evaluated, P.californica had the fewest shared neuropeptides with A.californica. Overall, the MCC transcriptome profile was highly conserved across species with orthologs found for transcription factors, ion channels, neuropeptides and the serotonergic biosynthesis genes. We also found numerous innovations in gene expression at the ganglia and single neuron levels, altogether allowing for a better understanding of how brains, novel circuits, and behaviors have evolved.
