PEANUT AGGLUTININ BINDING GLYCOPROTEINS IN THE CHICK RETINA - THEIR PRESENCE IN MULLER GLIA CELLS

The histological and cellular distribution and some biochemical characteristics of components that bind peanut agglutinin (PNA), a lectin that recognizes preferentially terminal galactose-beta (1-3) N-acetyl galactosamine disaccharide residues of glycoconjugates, were studied in chick retinal tissue and in dissociated retinal cells after their differentiation in culture. In sections of retinal tissue from animals 7 days after hatching (Rp7), in addition to the inner and outer segments of the photoreceptor layer, the plexiform and optic fiber layers were stained with rhodamine-labeled PNA, indicating that, besides photoreceptor cells, other cellular types contribute to the PNA staining. We present evidence indicating that at least part of this staining is provided by Muller glia cells. In cultures of dissociated cells from retinas at embryonic day 7 (R7), photoreceptor-like cells and flat Muller glia-derived cells but not neurons were stained with rhodamine-labeled PNA. Furthermore, Muller glia cells isolated from Rp7 were also brightly stained with PNA. Western blot assays of extracts from R7 showed the presence of PNA binding glycoproteins of 31-33 kDa and a component that migrates at the dye front. In addition to the components detected in R7, extracts from R14 and Rp7 showed the presence of a major PNA binding glycoprotein of 175 kDa and a minor glycoprotein of 220 kDa. Extracts from the photoreceptor layer contain the 175 and 220 kDa glycoproteins, indicating their association with photoreceptor cells. The 31-33 kDa components were detected in extracts from the remnant inner retina, suggesting their association with the Muller glia cells. Supporting this view, these components and not those of 175 and 220 kDa were detected in cell cultures enriched in flat Muller glia-derived cells. Only the 31-33 kDa components and the component that migrates at the dye front were detected in extracts from cell cultures enriched in photoreceptor-like cells, suggesting the need of some environmental element for the expression of the 175 and 220 kDa components in the differentiated photoreceptor cells.