The central nervous system of sea cucumbers (Echinodermata: Holothuroidea) shows positive immunostaining for a chordate glial secretion.
BACKGROUND
Echinoderms and chordates belong to the same monophyletic taxon, the Deuterostomia. In spite of significant differences in body plan organization, the two phyla may share more common traits than was thought previously. Of particular interest are the common features in the organization of the central nervous system. The present study employs two polyclonal antisera raised against bovine Reissner's substance (RS), a secretory product produced by glial cells of the subcomissural organ, to study RS-like immunoreactivity in the central nervous system of sea cucumbers.


RESULTS
In the ectoneural division of the nervous system, both antisera recognize the content of secretory vacuoles in the apical cytoplasm of the radial glia-like cells of the neuroepithelium and in the flattened glial cells of the non-neural epineural roof epithelium. The secreted immunopositive material seems to form a thin layer covering the cell apices. There is no accumulation of the immunoreactive material on the apical surface of the hyponeural neuroepithelium or the hyponeural roof epithelium. Besides labelling the supporting cells and flattened glial cells of the epineural roof epithelium, both anti-RS antisera reveal a previously unknown putative glial cell type within the neural parenchyma of the holothurian nervous system.


CONCLUSIONS
Our results show that: a) the glial cells of the holothurian tubular nervous system produce a material similar to Reissner's substance known to be synthesized by secretory glial cells in all chordates studied so far; b) the nervous system of sea cucumbers shows a previously unrealized complexity of glial organization. Our findings also provide significant clues for interpretation of the evolution of the nervous system in the Deuterostomia. It is suggested that echinoderms and chordates might have inherited the RS-producing radial glial cell type from the central nervous system of their common ancestor, i.e., the last common ancestor of all the Deuterostomia.
Mashanov
Vladimir S
VS
Department of Biology, University of Puerto Rico, P.O. Box 23360, UPR Station, Rio Piedras, PR 00931-3360, Puerto Rico.|Anatomische Anstalt, Ludwig-Maximilians-Universität München, Pettenkoferstrasse 11, D-80336 München, Germany.
Zueva
Olga R
OR
Department of Biology, University of Puerto Rico, P.O. Box 23360, UPR Station, Rio Piedras, PR 00931-3360, Puerto Rico.|Anatomische Anstalt, Ludwig-Maximilians-Universität München, Pettenkoferstrasse 11, D-80336 München, Germany.
Heinzeller
Thomas
T
Anatomische Anstalt, Ludwig-Maximilians-Universität München, Pettenkoferstrasse 11, D-80336 München, Germany.
Aschauer
Beate
B
Anatomische Anstalt, Ludwig-Maximilians-Universität München, Pettenkoferstrasse 11, D-80336 München, Germany.
Naumann
Wilfried W
WW
Institut für Zoologie, Universität Leipzig, Talstrasse 33, D-04103 Leipzig, Germany.
Grondona
Jesus M
JM
Laboratorio de Fisiología Animal. Departamento de Biología Celular, Genética y Fisiología. Facultad de Ciencias. Universidad de Málaga. 29071 Málaga. Spain.
Cifuentes
Manuel
M
Laboratorio de Fisiología Animal. Departamento de Biología Celular, Genética y Fisiología. Facultad de Ciencias. Universidad de Málaga. 29071 Málaga. Spain.
Garcia-Arraras
Jose E
JE
Department of Biology, University of Puerto Rico, P.O. Box 23360, UPR Station, Rio Piedras, PR 00931-3360, Puerto Rico.