Figure 1.

β5 integrin is expressed apically by the adult RPE but is not expressed at PN2. For reference, a methylene blue stained thick section with intact retina is shown at the top. Adult rat RPE: The subcellular distribution of integrin receptors or their subunits was determined on cryosections of adult rat eyes by indirect immunofluorescence. While β1 integrin receptors were exclusively basal (A, αxβ1), αv integrin receptors were localized on both apical and basolateral surface, as well an on cytoplasmic vesicles (A, αvβx). The αv subunit stained cytoplasm and all plasma membrane domains. Nonspecific IgG gave only background staining (A, control). The β5 integrin was detected only apically in the adult RPE (A, β5) while β3 integrin was restricted basally (A, β3). Note that β5 antibody immunostaining required methanol fixation after removal of the neural retina causing occasional disruption of the apical RPE surface. Immature rat RPE: at PN2 (B) β5 integrin was not detected (B, β5). In contrast, β3 integrin was expressed with a nonpolar distribution (B, β3). (Bars = 5 μm.)