Expression of glial fibrillary acidic protein by Müller cells in rd chick retina.

Accumulation of glial fibrillary acidic protein (GFAP) in Müller cells has been observed in retinas of several mammalian species secondary to genetically induced degeneration and neuronal injury. In the present series of experiments, I have examined the effects of the rd (retinal degeneration) mutation on the expression of GFAP in retinas of chicks homozygous for the mutation (rd/rd) prior to and following the onset of photoreceptor degeneration, which first appears approximately 7 days posthatch (7 dph). Carrier (+/rd) and wild-type (+/+) retinas served as controls. Retinas taken from 1, 7, 21, and 33 dph rd/rd, +/rd, and +/+ chicks were analyzed for the presence of GFAP by immunocytochemical and SDS-PAGE/Western blot techniques. The following immunocytochemical observations were made: (1) GFAP immunostaining was limited to and located throughout the Müller cells. (2) The intensity of GFAP immunostaining increased with age in all three retina types in tissue sections, as well as on immunoblots. (3) The distribution of GFAP staining within rd/rd Müller cells following the onset of degeneration was slightly different from that observed in +/+ and +/rd retinas and was distinguished by increased staining of the cell bodies and the cell processes forming the outer limiting membrane. The results of these experiments show that Müller cells in chick retina contain GFAP. In addition, they suggest that, in contrast to Müller cells in degenerating mammalian retina, Müller cells in rd chick retina do not accumulate large amounts of GFAP in response to degeneration.