Comparative anatomy of the cerebellar cortex in mice lacking vimentin, GFAP, and both vimentin and GFAP

In the cerebellum of adult mammals, glial fibrillary acidic protein (GFAP) and vimentin (VIM) are coexpressed in Golgi epithelial cells (GEC), also known as Bergmann glia. In this study we used three transgenic knockout mice (GFAP, VIM and double GFAP and VIM) to analyze the involvement of these proteins in the building of glial filaments and in neuron-glia interactions. The cerebella of VIM, GFAP, and GFAP/VIM mutant mice were processed by the rapid Golgi method and also for electron microscopy. In VIM mutant mice, Bergmann fibers are hypertrophic with thickened appendages. In the electron microscope they appear as large glial profiles devoid of glial filaments, with embedded dendritic thorns and parallel fiber boutons. In addition, signs of degeneration are observed in Purkinje cells. In GFAP mutant mice, GEC exhibit fine, delicate processes, as those seen in wild-type animals, however, a large accumulation of lamellae and granular appendages was observed along their surfaces, which came into contact with each other. The electron microscope exhibited fine and scarce astroglial profiles containing some glial filaments, a stunted glia limitans, and the presence of large extracellular spaces. In double mutant mice, the two phenotypes are expressed but appear attenuated, with a total absence of glial filaments and the general appearance of immaturity for GEC. In conclusion, it appears that the absence of each of the proteins yields a specific phenotype and that the defects are not necessarily additive.