Reissner's substance expressed as a transient pattern in vertebrate floor plate.

The function of the floor plate in dorso-ventral patterning of the developing nervous system and in the guidance of commissural axons is well established. However, several morphological aspects concerning the exact localization of its rostral and caudal end and the regional and temporal specialization are still controversial. We present new insights revealed by the expression of Reissner's substance in the floor plate during early neurogenesis of zebrafish, Xenopus, chick and rat. We used a polyclonal antiserum raised against Reissner's substance, which is a secretory product of radial glia in the roof plate of the adult vertebrate brain. In early embryonic stages the rostral boundary of floor plate immunoreaction vary in the different vertebrates. Immunoreactive cells are not only present in the epichordal region (rat) but also in prechordal areas of the midbrain (chick) and forebrain (zebrafish and Xenopus). During further development, Reissner's substance expression disappears first in the most rostral areas and later also in the spinal cord. However, immunopositive labelling in the isthmus region at the mes-metencephalic boundary, described originally as the flexural organ, is most extensive and detectable during a long period of embryonic development. It is proposed that the gradual restriction of Reissner's substance expression to the isthmus reflects the complex differentiation processes in this region also in later embryonic development. Furthermore, the expression pattern in zebrafish indicates that Reissner's substance could play a role in axonal decussation.

Role of tissue transglutaminase in gliadin binding to reticular extracellular matrix and relation to coeliac disease autoantibodies.

On different tissue sections, binding of gliadin to reticular matrix components was observed which was Ca2+-dependent, inhibited by Cu2+ and Zn2+ ions, by putrescine, and by preincubation with antibodies against tissue transglutaminase (tTG) suggesting that binding of gliadin is mediated by tTG. tTG was able to bind to gliadin and fibronectin fixed to microplates. Furthermore, tTG mediated binding of gliadin to fibronectin coated to microplates. On tissue sections, treatment with sera containing coeliac disease autoantibodies yielded staining patterns very similar to that of bound gliadin. Dual label experiments by means of conventional and laser scanning microscopy revealed that most of autoantibody binding sites are matched by bound gliadin. However, lack of competition between gliadin and autoantibody binding hints to ligands in very close vicinity of this enzyme. Furthermore, there were several autoantibody binding regions which did not bind gliadin. This implies the existence of further autoantigenic epitopes not related to tTG.

Radial secretory glia conserved in the postnatal vertebrate brain: a study in the rat.

Secretory glial cells in the roof of the last diencephalic prosomer, ependymocytes and hypendymocytes, form the subcommissural organ. The cells of this complex were labelled immunocytochemically, using an antiserum against their specific secretory products. The study aims at the characterization of this cell type in the rat as an anatomical model situation. Radially oriented secretory glial cells remain after birth behind the posterior commissure in the mesencephalic aqueduct. At about postnatal day 10, the cell bodies descend into the conventional ependyma and at postnatal day 25 they assume a compact, rounded appearance. The secretory product they release is involved in the formation of Reissner's fiber. This differentiation in phenotype is not accompanied by a change of the intermediate filament expression. In the adult rat these cells had been labelled immunopositive for cytokeratins 8 and 18 as well as vimentin but not for glial fibrillary acidic protein. DiI-marking from the third ventricle and from the dorsal surface of the brain shows that the basal processes of ependymocytes and hypendymocytes project to the external and internal glial limiting membrane, respectively, through the commissural fiber bundles. Also the subependymal located hypendymocytes have apical processes with contacts to the cerebrospinal fluid. When this secretory cell population is studied with respect to cyto-architectonical changes during ontogeny the results lead to a new understanding of the subcommissural cells. They are not specialized ependymal cells in a regionally restricted and secondary differentiated ependymal area, but rather descendants of an ontogenetically ancient, specific type of radial glia. Characteristic features for all subcommissural cells are that they: (1) appear very early during ontogeny, (2) are derived from a radial oriented glial cell type, (3) carry at least one kinocilium, (4) possess an original intermediate filament pattern, (5) release a secretory product.