Early evolution of radial glial cells in Bilateria.
Conrad Helm, Anett Karl, Patrick Beckers, Sabrina Kaul-Strehlow, Elke Ulbricht, Ioannis Kourtesis, Heidrun Kuhrt, Harald Hausen, Thomas Bartolomaeus, Andreas Reichenbach, Christoph Bleidorn
Author Information
Conrad Helm: Sars International Center for Marine Molecular Biology, University of Bergen, 5008 Bergen, Norway conrad.helm@uib.no. ORCID
Anett Karl: Paul-Flechsig-Institute for Brain Research, University of Leipzig, 04103 Leipzig, Germany.
Patrick Beckers: Institute of Evolutionary Biology and Ecology, University of Bonn, 53121 Bonn, Germany.
Sabrina Kaul-Strehlow: Department of Integrative Biology, University of Vienna, 1090 Vienna, Austria.
Elke Ulbricht: Biotechnology Center, Technische Universität Dresden, 01307 Dresden, Germany.
Ioannis Kourtesis: Sars International Center for Marine Molecular Biology, University of Bergen, 5008 Bergen, Norway.
Heidrun Kuhrt: Paul-Flechsig-Institute for Brain Research, University of Leipzig, 04103 Leipzig, Germany.
Harald Hausen: Sars International Center for Marine Molecular Biology, University of Bergen, 5008 Bergen, Norway.
Thomas Bartolomaeus: Institute of Evolutionary Biology and Ecology, University of Bonn, 53121 Bonn, Germany. ORCID
Andreas Reichenbach: Paul-Flechsig-Institute for Brain Research, University of Leipzig, 04103 Leipzig, Germany.
Christoph Bleidorn: Museo Nacional de Ciencias Naturales, Spanish National Research Council (CSIC), 28006 Madrid, Spain christoph.bleidorn@gmail.com.
Bilaterians usually possess a central nervous system, composed of neurons and supportive cells called glial cells. Whereas neuronal cells are highly comparable in all these animals, glial cells apparently differ, and in deuterostomes, radial glial cells are found. These particular secretory glial cells may represent the archetype of all (macro) glial cells and have not been reported from protostomes so far. This has caused controversial discussions of whether glial cells represent a homologous bilaterian characteristic or whether they (and thus, centralized nervous systems) evolved convergently in the two main clades of bilaterians. By using histology, transmission electron microscopy, immunolabelling and whole-mount hybridization, we show here that protostomes also possess radial glia-like cells, which are very likely to be homologous to those of deuterostomes. Moreover, our antibody staining indicates that the secretory character of radial glial cells is maintained throughout their various evolutionary adaptations. This implies an early evolution of radial glial cells in the last common ancestor of Protostomia and Deuterostomia. Furthermore, it suggests that an intraepidermal nervous system-composed of sensory cells, neurons and radial glial cells-was probably the plesiomorphic condition in the bilaterian ancestor.
