TRANSIENT INDUCTION OF THE GLIAL INTERMEDIATE FILAMENT PROTEIN GENE IN MULLER CELLS IN THE MOUSE RETINA

The glial intermediate filament protein (GFAP) gene is not normally ex pressed by retinal Muller cells but it is transcriptionally activated following photoreceptor degeneration. In the present study, we have ex amined the relationship between progressive photoreceptor loss and cha nges in GFAP gene activity in Muller cells, In albino mice with light- induced photoreceptor degeneration, GFAP level was strongly elevated a fter 2 weeks, GFAP level remained high even after 3 months in light, I n situ hybridization studies showed that GFAP transcripts were quite s parse in the first week but increased dramatically after 2 weeks of li ght exposure, After 4 weeks in constant light, however, little GFAP mR NA was detected in Muller cells, RNA blotting also showed that there w as an similar to 20-fold increase in GFAP mRNA content at 2 weeks; but at 4 weeks, the RNA content fell to about four-fold higher than the b asal level, These results show that GFAP level remains high long after its synthesis, probably as a consequence of low GFAP turnover in the Muller cell cytoskeleton, while GFAP mRNA level rises and declines rap idly due to transient activation of the GFAP gene in Muller cells.