Immunocytochemical localization of two retinoid-binding proteins in vertebrate retina.

Abstract

The recent discovery and characterization of several proteins that purify with endogenous, bound retinoid have given rise to the suggestion that these proteins, which are abundant in retina, perform a role in transport and function of vitamin A. Immunocytochemical techniques were used to localize two retinoid-binding proteins in the retina of four species. Antisera to cellular retinal-binding protein (CRALBP) and an interphotoreceptor retinoidbinding protein (IRBP) were obtained from rabbits immunized with antigens purified from bovine retina. Antibodies from each antiserum reacted with a single component in retinal homogenates and supernatants which corresponded to the molecular weight and charge of the respective antigen (non-SDS and SDS PAGE, electrophoretic transfer to nitrocellulose, immunochernical staining). Immunocytochemistry controls were antibodies from nonimmune serum and antibodies absorbed with purified antigen. Antigens were localized on frozensectioned bovine, rat, monkey, and human retina using immunofluorescence and the peroxidase-antiperoxidase technique. Specific staining with anti-IRBP was found in the space that surrounds photoreceptor outer segments, with heaviest labeling in a line corresponding to the retinal pigment epithelium (RPE) apical surface. Cone outer segments were positive. Staining with anti-CRALBP was found in two cell types in all species: the RPE and the M011er glial cell. Within the RPE, labeling filled the cytoplasm and was heaviest apically, with negative nuclei. Labeling of M011er cells produced Golgi-like silhouettes with intense staining of all cytoplasmic compartments. Staining of the external limiting membrane was heavy, with labeled microvilli projecting into the interphotoreceptor space. Localization of IRBP to this space bordered by three cell types (RPE, photoreceptor, and Mfiller) is consistent with its proposed role in transport of retinoids among cells. Localization of CRALBP in RPE corroborates previous biochemical studies; its presence in the MOiler cell suggests that this glial cell may play a hitherto unsuspected role in vitamin A metabolism in retina.

Chicken Retinas Contain a Retinoid Isomerase Activity that Catalyzes the Direct Conversion of all-trans-Retinol to 11-cis-Retinol

“…These cells were also shown to contain CRALBP (10,12). It is likely therefore that the retinol isomerase and palm-CoA-dependent retinyl ester synthase described here are located in Müller cells.…”

Platelet-Derived Growth Factor-A-Induced Retinal Gliosis Protects against Ischemic Retinopathy

“…27,28 Staining for cellular retinaldehyde-binding protein (a marker for Muller cells 29 ) showed no differences between rho/ PDGF-A2 or -A3 transgene-positive mice and wild-type mice (not shown).…”

Parallel visual cycles in the zebrafish retina

“…Müller glia cells have also been shown to express components involved in the canonical visual cycle, such as RGR (retinal G-protein coupled receptor) (Chen et al, 1996;Shen et al, 1994), and the retinoid binding proteins CRBP (cellular retinol binding protein) and CRALBP (cellular retinalaldehyde binding protein) (Bunt-Milam and Saari, 1983;Eisenfeld et al, 1985;Fleisch et al, 2008).…”

“…IRBP (interphotoreceptor retinoid-binding protein) is localized to the subretinal space (Loew and Gonzalez-Fernandez, 2002) and is known to be able to bind retinoids (Shaw and Noy, 2001). It therefore has been hypothesized to play a role in the transport of 11-cis RAL from the RPE to rod outer segments (Bunt-Milam and Saari, 1983;Fong et al, 1984;Lamb and Pugh, 2006;Pepperberg et al, 1993). Surprisingly, no evidence of an impairment of the canonical visual cycle has been found in irbp-/-mice (Palczewski et al, 1999;Ripps, 2001).…”

“…Transport of retinoids between the rod outer segment and the RPE (indicated by dashed arrows) is thought to involve the retinoid-binding protein IRBP (Bunt-Milam and Saari, 1983;Fong et al, 1984;Jin et al, 2009;Lamb and Pugh, 2006;Parker et al, 2009;Pepperberg et al, 1993). Bunt-Milam and Saari, 1983;Fong et al, 1984;Jin et al, 2009;Lamb and Pugh, 2006;Parker et al, 2009;Pepperberg et al, 1993). For a comprehensive review of the intra-retinal visual cycle please refer to (Muniz et al, 2007).…”