Synthesis of Interphotoreceptor Matrix I. Autoradiography of ³H-fucose incorporation

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Abstract

This study was undertaken in order to visualize the sites of synthesis of fucose-containing glycoproteins of the interphotoreceptor matrix (IPM). Posterior halves of eyes of ten day old and adult mice were incubated in vitro in medium containing ³H-fucose, followed by incubation in chase medium for periods up to two hours. Autoradiographs (ARG) were prepared for light and electron microscopy and interpreted as evidence of the synthesis and movement of fucose-containing glycoproteins. All retinal layers were labeled after the pulse, with nuclear layers being more heavily labeled than synoptic layers. The outer nuclear layer and inner segment region showed little variation in activity during the two hour incubation in the immature retina. The pigment epithelium (PE) showed a marked increase in radioactivity after the 15 minute chase in both the immature and adult retinas. This was interpreted to indicate synthesis of fucose-containing glycoprotein as well as transfer of radioactivity via phagocytosis from the outer segment-IPM region. A decline in radioactivity in the PE after the 30 minute chase and in the inner segment of adult photoreceptors after the 45 minute chase, was interpreted as movement of newly synthesized glycoprotein to their respective cell surfaces. This accounted for the rising radioactivity in the outer segment-IPM region at this time. Electron microscopic ARG indicate that the Golgi apparatus of the photoreceptors and the PE were prominently labeled at early time periods. Apical microvilli of the PE and the surface of outer segments were labeled, as were phagosomes and lysosomes. The functional significance of these findings is discussed.