Comparative immunohistochemical study of glial filament proteins (glial fibrillary acidic protein and vimentin) in goldfish, octopus, and snail.

Glial fibrillary acidic protein (GFAP) and vimentin proteins are known to be component proteins of glial filaments in the CNS of many vertebrates. The nature of the filaments present in the glial cells of the goldfish optic tectum and in the CNS of two members of the Mollusca (Helix pomatia and Octopus vulgaris) were investigated using immunocytochemical localization of monoclonal antibodies to GFAP and vimentin. Immunoblots visualized by the alkaline phosphatase method showed cross-reactive protein bands to GFAP and vimentin antibodies in total brain homogenates of the goldfish, octopus, and snail. Immunofluorescence staining of the goldfish optic tectum showed GFAP immunoreactivity, primarily in the ependymal cell processes. Immunogold labelling at the ultrastructural level verified that GFAP antibodies were bound to glial filaments. Immunolabelling of the optic lobe of Octopus vulgaris and the cerebral ganglia of Helix pomatia suggests that a protein exhibiting antigenic properties similar to GFAP is a component protein in the filaments of the protoplasmic and filamentous glia randomly distributed throughout the CNS. Unlike anti-GFAP antibodies, which stained relatively specific to filaments, vimentin staining in the CNS tissues of the three organisms studied did not appear to be exclusive to filamentous structures. As vimentin protein has been shown, in previous studies as well as our own, to exist in many tissue types, this suggests that it does not appear to be confined to glial filaments but is shared with other subcellular components. The proteins GFAP and vimentin which are thought to be well conserved in vertebrate evolution also appear to be expressed in the nervous system of some lower organisms.