Early in the evolution of bilaterian animals cell types diversified, giving rise to a wide range of cell type families which allow for the complexity of animals. Platynereis dumerilii, an annelid worm, is a powerful model for studying the evolution of cell types due to its phylogenetic location relative to other model organisms, and as it has retained many ancient characteristics. Additionally, Platynereis develops stereotypically, opening the door for correlative multimodal exploration.
We combine whole animal volume electron microscopy (SBEM) with whole mount in situ hybridization to build a cell type atlas for Platynereis at 6dpf. The ‘Platy Browser’ is an open access platform to explore the cells of Platynereis across the entire organism (approximately 12000 cells). The Browser can be expanded to include additional data from different modalities, including further EM sources such as volume EM from FIBSEM, which can provide higher resolution for subsections of the animal.
Clustering techniques can be used to analyze a combination of morphological features and gene expression profiles from the Browser to identify cell types. Unlike single cell sequencing cluster analysis, here we retain the spatial information of the clusters and can find back individual cells within the EM. Additionally morphological features alone can be analyses to determine if they are predictive of cell type. This resource provides valuable data for investigation into the evolution of cell types. Identifying gene expression profiles responsible for the morphology unique to particular cell types, or shared among sister cell types.