Glial fibrillary acidic protein and its mRNA: ultrastructural detection and determination of changes after CNS injury.

We have previously demonstrated that glial fibrillary acidic protein (GFAP) containing intermediate filaments in retinal Müller cells undergo both quantitative induction and subcellular reorganization as a response to long-term retinal detachment (an induced CNS degeneration wherein the Müller cells form a multicellular scar). This study demonstrates by RNA blotting analysis that normal retina expresses a low basal level of GFAP mRNA, which is induced approximately 500% within 3 days of retinal detachment. At the cellular level, electron microscopic in situ hybridization analysis readily detects GFAP mRNA in Müller cells of detached retinas, but not in normal retinas. On the other hand, GFAP mRNA was readily detected in retinal astrocytes (which appear to express GFAP mRNA at high, constitutive levels). In both cell types, the ultrastructural localization of GFAP mRNA was the same. In the nuclei, the GFAP mRNA was associated with amorphous, electron-dense regions within the euchromatin. In the cytoplasm, the GFAP mRNA was associated with intermediate filaments near the nuclear pores, along the filaments when no other structures were apparent, and when the filaments appeared to be associated with ribosomes and polysomes. The ultrastructural location of the GFAP mRNA (especially along the intermediate filaments) may be unique to this mRNA or may represent a more generalized mRNA phenomenon.