Meeting Abstract
How did the vast diversity of cell types arise during evolution and how are cell types related to each other? Addressing these questions, we study representatives of the phenotypically diverse superphylum Lophotrochozoa with clades as different as mollusks or annelids. The polyplacophoran mollusk Acanthochitona crinita exhibits ancestral molluscan and bilaterian traits. Its trochophore larva is a mosaic of embryonic and adult features such as seven shell plates, an apical organ, a ciliary band, a creeping foot, and a differentiated nervous system. In order to investigate the cellular organization of these ancestral traits we have conducted whole-body single cell transcriptomics on trochophore larvae using 10x genomics and Next-Seq technology. Approximately 8000 cells with 8000 mean reads per cell were obtained and more than 60 different cell types revealed which were localized via in situ hybridization experiments. Besides endodermal clusters, we identified mesodermal cell types giving rise to the complex polyplacophoran musculature. In addition, several ectodermal cell types including sensory cells, other neurons, and epidermal cells were found. Notably, cell types forming the shell fields and the surrounding spicules cluster together with neuronal cell clusters suggesting a shared evolutionary history. By comparing our data to those of other lophotrochozoan representatives we reveal putative homologous cell types. Our data lay the foundation for tracing the evolution of cell types and cell type families across Lophotrochozoa and Bilateria.
