Seminar "The evolution of ectodermal patterning systems and the homology of bilaterian nerve cords" by Dr Andreas Hejnol

Title: "The evolution of ectodermal patterning systems and the homology of bilaterian nerve cords"

Speaker: Dr Andreas Hejnol

Abstract: The presence of similar molecular patterns along the body axes of vertebrates, flies, and annelids grounds the scenario that a condensed nervous system with a medial ventral nerve cord is an ancestral character of Bilateria. However, whether these similarities are generally found across the vast diversity of bilaterian neuroanatomies is unclear, and thus the evolutionary history of the nervous system is still contentious. To assess the conservation of neuroectodermal patterning systems and their relation to the nerve cords, we studied representatives of the major bilaterian groups Xenacoelomorpha, Rotifera, Nemertea, Brachiopoda, and Annelida. While xenacoelomorphs already present the anteroposterior and dorsoventral patterns, none of the studied species shows a fully conserved mediolateral regionalization coupled to their specific trunk neuroanatomies. Therefore, our findings qualify the use of molecular patterns to explain nervous system evolution, supporting that similarities in mediolateral patterning and nerve cord configuration evolved independently in Bilateria.