Helm Conrad, Karl Anett, Beckers Patrick, Kaul-Strehlow Sabrina, Ulbricht Elke, Kourtesis Ioannis, Kuhrt Heidrun, Hausen Harald, Bartolomaeus Thomas, Reichenbach Andreas, Bleidorn Christoph
Sars International Center for Marine Molecular Biology, University of Bergen, 5008 Bergen, Norway
Paul-Flechsig-Institute for Brain Research, University of Leipzig, 04103 Leipzig, Germany.
Proc Biol Sci. 2017 Jul 26;284(1859). doi: 10.1098/rspb.2017.0743.
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.
两侧对称动物通常拥有一个中枢神经系统，由神经元和称为神经胶质细胞的支持细胞组成。尽管所有这些动物中的神经元细胞高度相似，但神经胶质细胞显然有所不同，在后口动物中发现了放射状胶质细胞。这些特殊的分泌性神经胶质细胞可能代表了所有（宏观）神经胶质细胞的原型，到目前为止，原口动物中尚未有相关报道。这引发了关于神经胶质细胞是否代表同源的两侧对称动物特征，或者它们（以及因此的集中化神经系统）是否在两侧对称动物的两个主要分支中趋同进化的争议性讨论。通过组织学、透射电子显微镜、免疫标记和整体杂交技术，我们在此表明原口动物也拥有放射状胶质样细胞，它们很可能与后口动物的放射状胶质细胞同源。此外，我们的抗体染色表明放射状胶质细胞的分泌特性在其各种进化适应过程中得以保留。这意味着放射状胶质细胞在原口动物和后口动物的最后共同祖先中就已早期进化。此外，这表明由感觉细胞、神经元和放射状胶质细胞组成的表皮内神经系统可能是两侧对称动物祖先的原始状态。
