CONTROL OF DROSOPHILA RETINOID AND FATTY-ACID-BINDING GLYCOPROTEIN EXPRESSION BY RETINOIDS AND RETINOIC ACID - NORTHERN, WESTERN AND IMMUNOCYTOCHEMICAL ANALYSES

In Drosophila, thorough retinoid deprivation is possible, optimizing i nvestigation of the effects of vitamin A metabolites and retinoic acid on the visual system. Retinoids had been found to control transcripti on and translation of Drosophila's opsin gene. To follow this line of inquiry, we examined the effect of retinoids on the translation and tr anscription of a Drosophila Retinoid and Fatty Acid Binding Glycoprote in. Western blots showed that this protein is high in retinoid replete flies and low in deprived flies. Flies grown on media capable of acti vating the opsin gene's transcription and which contain alternate tran scription activators including retinoic acid yielded extracts containi ng significant amounts of Retinoid and Fatty Acid Binding Glycoprotein . Immunocytochemistry confirmed its absence in deprived flies and its presence in flies reared or replaced on these diverse media containing retinoids or general nutrients. Immunocytochemistry localized Retinoi d and Fatty Acid Binding Glycoprotein to the Semper (cone) cells and t he intraommatidial matrix (the interphotoreceptor matrix of the ommati dium). Positive staining of Semper cells in mutants of the opsin gene and a mutant lacking receptors suggests that Retinoid and Fatty Acid B inding Glycoprotein does not depend on presence of opsin and that it i s not synthesized in receptor cells respectively. Northern blots demon strated greatly diminished mRNA for Retinoid and Fatty Acid Binding Gl ycoprotein in flies grown on deprivation food relative to flies grown on normal food. Although the synthesis of Retinoid and Fatty Acid Bind ing Glycoprotein does not require chromophore precursors as does that of opsin, the control of Retinoid and Fatty Acid Binding Glycoprotein and opsin transcription by retinoids including retinoic acid might ver y well be the same. Our results suggest that Retinoid and Fatty Acid B inding Glycoprotein may be involved in retinoid transport. Also, Sempe r cells may be analogous to vertebrate retinal pigment epithelium in r etinoid metabolism and/or delivery. (C) 1997 Academic Press Limited.