External seminar – Evelyn HOULISTON

Gianni LITI invite : Evelyn HOULISTON – Institut de la Mer de Villefranche-sur-mer (IMEV)

« Origins and evolution of neurogenesis : lessons from the cnidarian Clytia hemisphaerica« 

Abstract: Clytia hemisphaerica is a hydrozoan jellyfish species that has gradually emerged as a laboratory model over the last 20 years.  Defined strains, including ones genetically manipulated using CRISPR-Cas9, can be conveniently cultured as ‘immortal’, vegetatively-propagating polyp colonies, providing a constant supply of genetically uniform jellyfish by constant budding. Adult Clytia jellyfish then reliably provide daily batches of large (180 µm diameter), transparent eggs, which are robust to manipulate and develop reliably to form first the ‘planula’ larva, and then via metamorphosis the polyp stage.  Our group’s original motivation to culture Clytia was to exploit these practical features to study the cellular and molecular basis embryonic axis specification, but our investment in techniques and resources has provided a platform for further studies on many topics by ourselves and others, including gametogenesis, morphogenesis, regeneration and neurobiology. The findings of these studies each add morsels of new information to help chart the evolution of developmental mechanisms in animals. I will illustrate this through recent studies on the developmental origins of neural cells, which revealed two distinct neurogenesis pathways operating in parallel during formation of the Clytia larva. Clytia thus joins other cnidarian laboratory species, each with their distinct developmental modes and phylogenetic positions, in expanding the available comparative framework required for understanding animal development and evolution.