SECRETORY RADIAL GLIA IN THE ECTONEURAL SYSTEM OF THE SEA STAR ASTERIAS-RUBENS (ECHINODERMATA)

Previous studies of epithelial nervous systems have focused on the neu ronal elements, but generally neglected the origin of neuro-glial inte ractions. In this study, we use a polyclonal antiserum directed agains t Reissner's substance to label non-neuronal bipolar cells in the ecto neural part of the radial nerve cord in the sea star Asterias rubens. Ultrastructural results show secretory activity in these bipolar cells . Immunolabelled material is released into the extracellular matrix in the hyaline layer as well as in the region of the basal end-feet. As a first step towards characterising the antigen, a specific protein ba nd of 36 kD was demonstrated with immunoprecipitation. Cells of this t ype: (1) traverse the epithelium to full extent from the outer surface to the basal lamina; (2) carry a single apical cilium; (3) contain co nspicuous bundles of intermediate filament; (4) produce a secretion wh ich is, at least in part, homologous to the Reissner's substance which is produced by a primitive radial glia cell type in chordates. It is concluded that the bipolar cells in the ectoneural part of the surface epithelium of the sea star Asterias rubens are secretory radial glia, which evidently have a common origin to the radial glia which secrete s Reissner's substance in chordates. (C) 1998 The Royal Swedish Academ y of Sciences. Published by Elsevier Science Ltd. All rights reserved.