Detlev Arendt - 2022/08/17

Tracking cellular identities through bilaterian brain evolution

Abstract:

We are interested in the evolution of animal bodies and, in particular, in the origin and rise of their most fascinating trait, which is the centralized nervous system. For this, we track the evolution of neurons and other constituent cell types across animal phylogeny, focusing on slow-evolving animals with moderate amounts of secondary loss. The nereid Platynereis dumerilii is a powerful model for comparative studies, with morphologically similar organisms already existing in the Cambrian. Taking advantage of its highly stereotypic development, we have established a link between cellular gene expression and ultrastructure for the entire body of a three-segmented young worm – via the spatial registration of a high-resolution serial block-face electron microscopy dataset to a whole-body cellular gene expression atlas for 6dpf Platynereis. To systematically characterize cellular morphologies we have also added AI-based recognition of cellular MorphoFeatures to the atlas that we can now align with cell type-specific gene modules. Furthermore, we are mapping single-cell omics data onto segmented cells in the EM volume to correlate cell type-specific expression programs and MorphoFeatures. 

I will explain how these unique resources allow us to identify hotspots of cellular variation both at the micro- and macroevolutionary scale, and to thus track the changes in cellular identities and phenotypes that govern neuron type and CNS evolution. My focus will be on the head sensory organs and the brain, where I will highlight a series of duplication events that have driven cell type diversification, and explain what we can learn from this about the evolution of cellular identities.