The evolutionary origin of neuronal signalling machinery and animal cell differentiation

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• Dr Pawel Burkhardt (Sars Centre, University of Bergen)
• Wednesday 26 April 2023, 13:00-14:00
• Online.

If you have a question about this talk, please contact Nadine Randel.

Multicellularity evolved multiple times independently in eukaryotes. Choanoflagellates are the closest single-celled relatives of animals. Strikingly, these tiny protists can not only alternate between unicellular and multicellular states, but also express many genes previously thought to be animal specific (e.g., cadherins, tyrosine kinases, synaptic proteins), making choanoflagellates powerful models to investigate the origin of animal multicellularity, the mechanisms underlying cell differentiation and the ancestry of the neuronal protein machinery. In the first part of my talk, I will show that both, temporal and spatial cell type differentiation was likely present in the stem lineage leading to animals. We have reconstructed entire choanoflagellates and sponge choanocyte cells in 3D through transmission electron microscopy on serial ultrathin sections. Our work has revealed several surprises about cell differentiation in choanoflagellates and constitute an important step in reconstructing the cell biology of the last common ancestor of animals. In the second part of my talk, I will present our recent discoveries on neuronal protein homologs found in choanoflagellates and ctenophores. We have biochemically and structurally characterized several neuronal protein complexes from choanoflagellates and gained insights into their molecular mechanism. In the last part of my talk, I will present ultrastructural data on the ctenophore nervous system. Our analysis indicates that the ctenophore nerve net is wired in a different way to what is known from other animals. These results challenge the paradigm of neuronal network activity emerging through cellular diversification and provide insights into how many ways to build a neural network. Together, our work highlights the importance to include the closest unicellular relatives of animals to understand the evolutionary origin of animal cell differentiation and demonstrates that choanoflagellates and ctenophores are at the center stage to understand the evolution of neuronal machinery and first neurons.

This talk is part of the Evolution and Development Seminar Series series.

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